[PATCH 0/2] dma-buf: Add an API for exporting sync files (v14)

[PATCH 0/2] dma-buf: Add an API for exporting sync files (v14)

[Jason Ekstrand]

Modern userspace APIs like Vulkan are built on an explicit synchronization
model.  This doesn't always play nicely with the implicit synchronization used
in the kernel and assumed by X11 and Wayland.  The client -> compositor half
of the synchronization isn't too bad, at least on intel, because we can
control whether or not i915 synchronizes on the buffer and whether or not it's
considered written.

The harder part is the compositor -> client synchronization when we get the
buffer back from the compositor.  We're required to be able to provide the
client with a VkSemaphore and VkFence representing the point in time where the
window system (compositor and/or display) finished using the buffer.  With
current APIs, it's very hard to do this in such a way that we don't get
confused by the Vulkan driver's access of the buffer.  In particular, once we
tell the kernel that we're rendering to the buffer again, any CPU waits on the
buffer or GPU dependencies will wait on some of the client rendering and not
just the compositor.

This new IOCTL solves this problem by allowing us to get a snapshot of the
implicit synchronization state of a given dma-buf in the form of a sync file.
It's effectively the same as a poll() or I915_GEM_WAIT only, instead of CPU
waiting directly, it encapsulates the wait operation, at the current moment in
time, in a sync_file so we can check/wait on it later.  As long as the Vulkan
driver does the sync_file export from the dma-buf before we re-introduce it
for rendering, it will only contain fences from the compositor or display.
This allows to accurately turn it into a VkFence or VkSemaphore without any
over-synchronization.

This patch series actually contains two new ioctls.  There is the export one
mentioned above as well as an RFC for an import ioctl which provides the other
half.  The intention is to land the export ioctl since it seems like there's
no real disagreement on that one.  The import ioctl, however, has a lot of
debate around it so it's intended to be RFC-only for now.

Mesa MR: https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4037
IGT tests: https://patchwork.freedesktop.org/series/90490/

v10 (Jason Ekstrand, Daniel Vetter):
 - Add reviews/acks
 - Add a patch to rename _rcu to _unlocked
 - Split things better so import is clearly RFC status

v11 (Daniel Vetter):
 - Add more CCs to try and get maintainers
 - Add a patch to document DMA_BUF_IOCTL_SYNC
 - Generally better docs
 - Use separate structs for import/export (easier to document)
 - Fix an issue in the import patch

v12 (Daniel Vetter):
 - Better docs for DMA_BUF_IOCTL_SYNC

v12 (Christian König):
 - Drop the rename patch in favor of Christian's series
 - Add a comment to the commit message for the dma-buf sync_file export
   ioctl saying why we made it an ioctl on dma-buf

v13 (Jason Ekstrand):
 - Rebase on Christian König's fence rework

v14 (Daniel Vetter and Christian König):
 - Use dma_rev_usage_rw to get the properly inverted usage to pass to
   dma_resv_get_singleton() for export
 - Clean up the sync_file and fd if copy_to_user() fails
 - Fix -EINVAL checks for the flags parameter in import
 - Add documentation about read/write fences for import
 - Add documentation about the expected usage of import/export and
   specifically call out the possible userspace race.

Jason Ekstrand (2):
  dma-buf: Add an API for exporting sync files (v14)
  dma-buf: Add an API for importing sync files (v9)

 drivers/dma-buf/dma-buf.c    | 106 +++++++++++++++++++++++++++++++++++
 include/uapi/linux/dma-buf.h |  84 +++++++++++++++++++++++++++
 2 files changed, 190 insertions(+)

-- 
2.36.0

[PATCH 1/2] dma-buf: Add an API for exporting sync files (v14)

[Jason Ekstrand]

Modern userspace APIs like Vulkan are built on an explicit
synchronization model.  This doesn't always play nicely with the
implicit synchronization used in the kernel and assumed by X11 and
Wayland.  The client -> compositor half of the synchronization isn't too
bad, at least on intel, because we can control whether or not i915
synchronizes on the buffer and whether or not it's considered written.

The harder part is the compositor -> client synchronization when we get
the buffer back from the compositor.  We're required to be able to
provide the client with a VkSemaphore and VkFence representing the point
in time where the window system (compositor and/or display) finished
using the buffer.  With current APIs, it's very hard to do this in such
a way that we don't get confused by the Vulkan driver's access of the
buffer.  In particular, once we tell the kernel that we're rendering to
the buffer again, any CPU waits on the buffer or GPU dependencies will
wait on some of the client rendering and not just the compositor.

This new IOCTL solves this problem by allowing us to get a snapshot of
the implicit synchronization state of a given dma-buf in the form of a
sync file.  It's effectively the same as a poll() or I915_GEM_WAIT only,
instead of CPU waiting directly, it encapsulates the wait operation, at
the current moment in time, in a sync_file so we can check/wait on it
later.  As long as the Vulkan driver does the sync_file export from the
dma-buf before we re-introduce it for rendering, it will only contain
fences from the compositor or display.  This allows to accurately turn
it into a VkFence or VkSemaphore without any over-synchronization.

By making this an ioctl on the dma-buf itself, it allows this new
functionality to be used in an entirely driver-agnostic way without
having access to a DRM fd. This makes it ideal for use in driver-generic
code in Mesa or in a client such as a compositor where the DRM fd may be
hard to reach.

v2 (Jason Ekstrand):
 - Use a wrapper dma_fence_array of all fences including the new one
   when importing an exclusive fence.

v3 (Jason Ekstrand):
 - Lock around setting shared fences as well as exclusive
 - Mark SIGNAL_SYNC_FILE as a read-write ioctl.
 - Initialize ret to 0 in dma_buf_wait_sync_file

v4 (Jason Ekstrand):
 - Use the new dma_resv_get_singleton helper

v5 (Jason Ekstrand):
 - Rename the IOCTLs to import/export rather than wait/signal
 - Drop the WRITE flag and always get/set the exclusive fence

v6 (Jason Ekstrand):
 - Drop the sync_file import as it was all-around sketchy and not nearly
   as useful as import.
 - Re-introduce READ/WRITE flag support for export
 - Rework the commit message

v7 (Jason Ekstrand):
 - Require at least one sync flag
 - Fix a refcounting bug: dma_resv_get_excl() doesn't take a reference
 - Use _rcu helpers since we're accessing the dma_resv read-only

v8 (Jason Ekstrand):
 - Return -ENOMEM if the sync_file_create fails
 - Predicate support on IS_ENABLED(CONFIG_SYNC_FILE)

v9 (Jason Ekstrand):
 - Add documentation for the new ioctl

v10 (Jason Ekstrand):
 - Go back to dma_buf_sync_file as the ioctl struct name

v11 (Daniel Vetter):
 - Go back to dma_buf_export_sync_file as the ioctl struct name
 - Better kerneldoc describing what the read/write flags do

v12 (Christian König):
 - Document why we chose to make it an ioctl on dma-buf

v13 (Jason Ekstrand):
 - Rebase on Christian König's fence rework

v14 (Daniel Vetter & Christian König):
 - Use dma_rev_usage_rw to get the properly inverted usage to pass to
   dma_resv_get_singleton()
 - Clean up the sync_file and fd if copy_to_user() fails

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Signed-off-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Acked-by: Simon Ser <contact@emersion.fr>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
---
 drivers/dma-buf/dma-buf.c    | 67 ++++++++++++++++++++++++++++++++++++
 include/uapi/linux/dma-buf.h | 35 +++++++++++++++++++
 2 files changed, 102 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 79795857be3e..6ff54f7e6119 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -20,6 +20,7 @@
 #include <linux/debugfs.h>
 #include <linux/module.h>
 #include <linux/seq_file.h>
+#include <linux/sync_file.h>
 #include <linux/poll.h>
 #include <linux/dma-resv.h>
 #include <linux/mm.h>
@@ -192,6 +193,9 @@ static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
  * Note that this only signals the completion of the respective fences, i.e. the
  * DMA transfers are complete. Cache flushing and any other necessary
  * preparations before CPU access can begin still need to happen.
+ *
+ * As an alternative to poll(), the set of fences on DMA buffer can be
+ * exported as a &sync_file using &dma_buf_sync_file_export.
  */
 
 static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
@@ -326,6 +330,64 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
 	return 0;
 }
 
+#if IS_ENABLED(CONFIG_SYNC_FILE)
+static long dma_buf_export_sync_file(struct dma_buf *dmabuf,
+				     void __user *user_data)
+{
+	struct dma_buf_export_sync_file arg;
+	enum dma_resv_usage usage;
+	struct dma_fence *fence = NULL;
+	struct sync_file *sync_file;
+	int fd, ret;
+
+	if (copy_from_user(&arg, user_data, sizeof(arg)))
+		return -EFAULT;
+
+	if (arg.flags & ~DMA_BUF_SYNC_RW)
+		return -EINVAL;
+
+	if ((arg.flags & DMA_BUF_SYNC_RW) == 0)
+		return -EINVAL;
+
+	fd = get_unused_fd_flags(O_CLOEXEC);
+	if (fd < 0)
+		return fd;
+
+	usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
+	ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
+	if (ret)
+		goto err_put_fd;
+
+	if (!fence)
+		fence = dma_fence_get_stub();
+
+	sync_file = sync_file_create(fence);
+
+	dma_fence_put(fence);
+
+	if (!sync_file) {
+		ret = -ENOMEM;
+		goto err_put_fd;
+	}
+
+	arg.fd = fd;
+	if (copy_to_user(user_data, &arg, sizeof(arg))) {
+		ret = -EFAULT;
+		goto err_put_file;
+	}
+
+	fd_install(fd, sync_file->file);
+
+	return 0;
+
+err_put_file:
+	fput(sync_file->file);
+err_put_fd:
+	put_unused_fd(fd);
+	return ret;
+}
+#endif
+
 static long dma_buf_ioctl(struct file *file,
 			  unsigned int cmd, unsigned long arg)
 {
@@ -369,6 +431,11 @@ static long dma_buf_ioctl(struct file *file,
 	case DMA_BUF_SET_NAME_B:
 		return dma_buf_set_name(dmabuf, (const char __user *)arg);
 
+#if IS_ENABLED(CONFIG_SYNC_FILE)
+	case DMA_BUF_IOCTL_EXPORT_SYNC_FILE:
+		return dma_buf_export_sync_file(dmabuf, (void __user *)arg);
+#endif
+
 	default:
 		return -ENOTTY;
 	}
diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h
index 8e4a2ca0bcbf..46f1e3e98b02 100644
--- a/include/uapi/linux/dma-buf.h
+++ b/include/uapi/linux/dma-buf.h
@@ -85,6 +85,40 @@ struct dma_buf_sync {
 
 #define DMA_BUF_NAME_LEN	32
 
+/**
+ * struct dma_buf_export_sync_file - Get a sync_file from a dma-buf
+ *
+ * Userspace can perform a DMA_BUF_IOCTL_EXPORT_SYNC_FILE to retrieve the
+ * current set of fences on a dma-buf file descriptor as a sync_file.  CPU
+ * waits via poll() or other driver-specific mechanisms typically wait on
+ * whatever fences are on the dma-buf at the time the wait begins.  This
+ * is similar except that it takes a snapshot of the current fences on the
+ * dma-buf for waiting later instead of waiting immediately.  This is
+ * useful for modern graphics APIs such as Vulkan which assume an explicit
+ * synchronization model but still need to inter-operate with dma-buf.
+ */
+struct dma_buf_export_sync_file {
+	/**
+	 * @flags: Read/write flags
+	 *
+	 * Must be DMA_BUF_SYNC_READ, DMA_BUF_SYNC_WRITE, or both.
+	 *
+	 * If DMA_BUF_SYNC_READ is set and DMA_BUF_SYNC_WRITE is not set,
+	 * the returned sync file waits on any writers of the dma-buf to
+	 * complete.  Waiting on the returned sync file is equivalent to
+	 * poll() with POLLIN.
+	 *
+	 * If DMA_BUF_SYNC_WRITE is set, the returned sync file waits on
+	 * any users of the dma-buf (read or write) to complete.  Waiting
+	 * on the returned sync file is equivalent to poll() with POLLOUT.
+	 * If both DMA_BUF_SYNC_WRITE and DMA_BUF_SYNC_READ are set, this
+	 * is equivalent to just DMA_BUF_SYNC_WRITE.
+	 */
+	__u32 flags;
+	/** @fd: Returned sync file descriptor */
+	__s32 fd;
+};
+
 #define DMA_BUF_BASE		'b'
 #define DMA_BUF_IOCTL_SYNC	_IOW(DMA_BUF_BASE, 0, struct dma_buf_sync)
 
@@ -94,5 +128,6 @@ struct dma_buf_sync {
 #define DMA_BUF_SET_NAME	_IOW(DMA_BUF_BASE, 1, const char *)
 #define DMA_BUF_SET_NAME_A	_IOW(DMA_BUF_BASE, 1, u32)
 #define DMA_BUF_SET_NAME_B	_IOW(DMA_BUF_BASE, 1, u64)
+#define DMA_BUF_IOCTL_EXPORT_SYNC_FILE	_IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file)
 
 #endif
-- 
2.36.0

[PATCH 2/2] dma-buf: Add an API for importing sync files (v9)

[Jason Ekstrand]

This patch is analogous to the previous sync file export patch in that
it allows you to import a sync_file into a dma-buf.  Unlike the previous
patch, however, this does add genuinely new functionality to dma-buf.
Without this, the only way to attach a sync_file to a dma-buf is to
submit a batch to your driver of choice which waits on the sync_file and
claims to write to the dma-buf.  Even if said batch is a no-op, a submit
is typically way more overhead than just attaching a fence.  A submit
may also imply extra synchronization with other work because it happens
on a hardware queue.

In the Vulkan world, this is useful for dealing with the out-fence from
vkQueuePresent.  Current Linux window-systems (X11, Wayland, etc.) all
rely on dma-buf implicit sync.  Since Vulkan is an explicit sync API, we
get a set of fences (VkSemaphores) in vkQueuePresent and have to stash
those as an exclusive (write) fence on the dma-buf.  We handle it in
Mesa today with the above mentioned dummy submit trick.  This ioctl
would allow us to set it directly without the dummy submit.

This may also open up possibilities for GPU drivers to move away from
implicit sync for their kernel driver uAPI and instead provide sync
files and rely on dma-buf import/export for communicating with other
implicit sync clients.

We make the explicit choice here to only allow setting RW fences which
translates to an exclusive fence on the dma_resv.  There's no use for
read-only fences for communicating with other implicit sync userspace
and any such attempts are likely to be racy at best.  When we got to
insert the RW fence, the actual fence we set as the new exclusive fence
is a combination of the sync_file provided by the user and all the other
fences on the dma_resv.  This ensures that the newly added exclusive
fence will never signal before the old one would have and ensures that
we don't break any dma_resv contracts.  We require userspace to specify
RW in the flags for symmetry with the export ioctl and in case we ever
want to support read fences in the future.

There is one downside here that's worth documenting:  If two clients
writing to the same dma-buf using this API race with each other, their
actions on the dma-buf may happen in parallel or in an undefined order.
Both with and without this API, the pattern is the same:  Collect all
the fences on dma-buf, submit work which depends on said fences, and
then set a new exclusive (write) fence on the dma-buf which depends on
said work.  The difference is that, when it's all handled by the GPU
driver's submit ioctl, the three operations happen atomically under the
dma_resv lock.  If two userspace submits race, one will happen before
the other.  You aren't guaranteed which but you are guaranteed that
they're strictly ordered.  If userspace manages the fences itself, then
these three operations happen separately and the two render operations
may happen genuinely in parallel or get interleaved.  However, this is a
case of userspace racing with itself.  As long as we ensure userspace
can't back the kernel into a corner, it should be fine.

v2 (Jason Ekstrand):
 - Use a wrapper dma_fence_array of all fences including the new one
   when importing an exclusive fence.

v3 (Jason Ekstrand):
 - Lock around setting shared fences as well as exclusive
 - Mark SIGNAL_SYNC_FILE as a read-write ioctl.
 - Initialize ret to 0 in dma_buf_wait_sync_file

v4 (Jason Ekstrand):
 - Use the new dma_resv_get_singleton helper

v5 (Jason Ekstrand):
 - Rename the IOCTLs to import/export rather than wait/signal
 - Drop the WRITE flag and always get/set the exclusive fence

v6 (Jason Ekstrand):
 - Split import and export into separate patches
 - New commit message

v7 (Daniel Vetter):
 - Fix the uapi header to use the right struct in the ioctl
 - Use a separate dma_buf_import_sync_file struct
 - Add kerneldoc for dma_buf_import_sync_file

v8 (Jason Ekstrand):
 - Rebase on Christian König's fence rework

v9 (Daniel Vetter):
 - Fix -EINVAL checks for the flags parameter
 - Add documentation about read/write fences
 - Add documentation about the expected usage of import/export and
   specifically call out the possible userspace race.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Signed-off-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
---
 drivers/dma-buf/dma-buf.c    | 39 ++++++++++++++++++++++++++++
 include/uapi/linux/dma-buf.h | 49 ++++++++++++++++++++++++++++++++++++
 2 files changed, 88 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 6ff54f7e6119..f23f1482eb38 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -386,6 +386,43 @@ static long dma_buf_export_sync_file(struct dma_buf *dmabuf,
 	put_unused_fd(fd);
 	return ret;
 }
+
+static long dma_buf_import_sync_file(struct dma_buf *dmabuf,
+				     const void __user *user_data)
+{
+	struct dma_buf_import_sync_file arg;
+	struct dma_fence *fence;
+	enum dma_resv_usage usage;
+	int ret = 0;
+
+	if (copy_from_user(&arg, user_data, sizeof(arg)))
+		return -EFAULT;
+
+	if (arg.flags & ~DMA_BUF_SYNC_RW)
+		return -EINVAL;
+
+	if ((arg.flags & DMA_BUF_SYNC_RW) == 0)
+		return -EINVAL;
+
+	fence = sync_file_get_fence(arg.fd);
+	if (!fence)
+		return -EINVAL;
+
+	usage = (arg.flags & DMA_BUF_SYNC_WRITE) ? DMA_RESV_USAGE_WRITE :
+						   DMA_RESV_USAGE_READ;
+
+	dma_resv_lock(dmabuf->resv, NULL);
+
+	ret = dma_resv_reserve_fences(dmabuf->resv, 1);
+	if (!ret)
+		dma_resv_add_fence(dmabuf->resv, fence, usage);
+
+	dma_resv_unlock(dmabuf->resv);
+
+	dma_fence_put(fence);
+
+	return ret;
+}
 #endif
 
 static long dma_buf_ioctl(struct file *file,
@@ -434,6 +471,8 @@ static long dma_buf_ioctl(struct file *file,
 #if IS_ENABLED(CONFIG_SYNC_FILE)
 	case DMA_BUF_IOCTL_EXPORT_SYNC_FILE:
 		return dma_buf_export_sync_file(dmabuf, (void __user *)arg);
+	case DMA_BUF_IOCTL_IMPORT_SYNC_FILE:
+		return dma_buf_import_sync_file(dmabuf, (const void __user *)arg);
 #endif
 
 	default:
diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h
index 46f1e3e98b02..70e213a0d7d9 100644
--- a/include/uapi/linux/dma-buf.h
+++ b/include/uapi/linux/dma-buf.h
@@ -96,6 +96,24 @@ struct dma_buf_sync {
  * dma-buf for waiting later instead of waiting immediately.  This is
  * useful for modern graphics APIs such as Vulkan which assume an explicit
  * synchronization model but still need to inter-operate with dma-buf.
+ *
+ * The intended usage pattern is the following:
+ *
+ *  1. Export a sync_file with flags corresponding to the expected GPU usage
+ *     via DMA_BUF_IOCTL_EXPORT_SYNC_FILE.
+ *
+ *  2. Submit rendering work which uses the dma-buf.  The work should wait on
+ *     the exported sync file before rendering and produce another sync_file
+ *     when complete.
+ *
+ *  3. Import the rendering-complete sync_file into the dma-buf with flags
+ *     corresponding to the GPU usage via DMA_BUF_IOCTL_EXPORT_SYNC_FILE.
+ *
+ * Unlike doing implicit synchronization via a GPU kernel driver's exec ioctl,
+ * the above is not a single atomic operation.  If userspace wants to ensure
+ * ordering via these fences, it is the respnosibility of userspace to use
+ * locks or other mechanisms to ensure that no other context adds fences or
+ * submits work between steps 1 and 3 above.
  */
 struct dma_buf_export_sync_file {
 	/**
@@ -119,6 +137,36 @@ struct dma_buf_export_sync_file {
 	__s32 fd;
 };
 
+/**
+ * struct dma_buf_import_sync_file - Insert a sync_file into a dma-buf
+ *
+ * Userspace can perform a DMA_BUF_IOCTL_IMPORT_SYNC_FILE to insert a
+ * sync_file into a dma-buf for the purposes of implicit synchronization
+ * with other dma-buf consumers.  This allows clients using explicitly
+ * synchronized APIs such as Vulkan to inter-op with dma-buf consumers
+ * which expect implicit synchronization such as OpenGL or most media
+ * drivers/video.
+ */
+struct dma_buf_import_sync_file {
+	/**
+	 * @flags: Read/write flags
+	 *
+	 * Must be DMA_BUF_SYNC_READ, DMA_BUF_SYNC_WRITE, or both.
+	 *
+	 * If DMA_BUF_SYNC_READ is set and DMA_BUF_SYNC_WRITE is not set,
+	 * this inserts the sync_file as a read-only fence.  Any subsequent
+	 * implicitly synchronized writes to this dma-buf will wait on this
+	 * fence but reads will not.
+	 *
+	 * If DMA_BUF_SYNC_WRITE is set, this inserts the sync_file as a
+	 * write fence.  All subsequent implicitly synchronized access to
+	 * this dma-buf will wait on this fence.
+	 */
+	__u32 flags;
+	/** @fd: Sync file descriptor */
+	__s32 fd;
+};
+
 #define DMA_BUF_BASE		'b'
 #define DMA_BUF_IOCTL_SYNC	_IOW(DMA_BUF_BASE, 0, struct dma_buf_sync)
 
@@ -129,5 +177,6 @@ struct dma_buf_export_sync_file {
 #define DMA_BUF_SET_NAME_A	_IOW(DMA_BUF_BASE, 1, u32)
 #define DMA_BUF_SET_NAME_B	_IOW(DMA_BUF_BASE, 1, u64)
 #define DMA_BUF_IOCTL_EXPORT_SYNC_FILE	_IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file)
+#define DMA_BUF_IOCTL_IMPORT_SYNC_FILE	_IOW(DMA_BUF_BASE, 3, struct dma_buf_import_sync_file)
 
 #endif
-- 
2.36.0

Re: [PATCH 1/2] dma-buf: Add an API for exporting sync files (v14)

[Christian König]

Reviewed-by: Christian König <christian.koenig@amd.com> for the series.

I assume you have the userspace part ready as well? If yes let's push 
this to drm-misc-next asap.

Christian.

Am 06.05.22 um 20:02 schrieb Jason Ekstrand:
> Modern userspace APIs like Vulkan are built on an explicit
> synchronization model.  This doesn't always play nicely with the
> implicit synchronization used in the kernel and assumed by X11 and
> Wayland.  The client -> compositor half of the synchronization isn't too
> bad, at least on intel, because we can control whether or not i915
> synchronizes on the buffer and whether or not it's considered written.
>
> The harder part is the compositor -> client synchronization when we get
> the buffer back from the compositor.  We're required to be able to
> provide the client with a VkSemaphore and VkFence representing the point
> in time where the window system (compositor and/or display) finished
> using the buffer.  With current APIs, it's very hard to do this in such
> a way that we don't get confused by the Vulkan driver's access of the
> buffer.  In particular, once we tell the kernel that we're rendering to
> the buffer again, any CPU waits on the buffer or GPU dependencies will
> wait on some of the client rendering and not just the compositor.
>
> This new IOCTL solves this problem by allowing us to get a snapshot of
> the implicit synchronization state of a given dma-buf in the form of a
> sync file.  It's effectively the same as a poll() or I915_GEM_WAIT only,
> instead of CPU waiting directly, it encapsulates the wait operation, at
> the current moment in time, in a sync_file so we can check/wait on it
> later.  As long as the Vulkan driver does the sync_file export from the
> dma-buf before we re-introduce it for rendering, it will only contain
> fences from the compositor or display.  This allows to accurately turn
> it into a VkFence or VkSemaphore without any over-synchronization.
>
> By making this an ioctl on the dma-buf itself, it allows this new
> functionality to be used in an entirely driver-agnostic way without
> having access to a DRM fd. This makes it ideal for use in driver-generic
> code in Mesa or in a client such as a compositor where the DRM fd may be
> hard to reach.
>
> v2 (Jason Ekstrand):
>   - Use a wrapper dma_fence_array of all fences including the new one
>     when importing an exclusive fence.
>
> v3 (Jason Ekstrand):
>   - Lock around setting shared fences as well as exclusive
>   - Mark SIGNAL_SYNC_FILE as a read-write ioctl.
>   - Initialize ret to 0 in dma_buf_wait_sync_file
>
> v4 (Jason Ekstrand):
>   - Use the new dma_resv_get_singleton helper
>
> v5 (Jason Ekstrand):
>   - Rename the IOCTLs to import/export rather than wait/signal
>   - Drop the WRITE flag and always get/set the exclusive fence
>
> v6 (Jason Ekstrand):
>   - Drop the sync_file import as it was all-around sketchy and not nearly
>     as useful as import.
>   - Re-introduce READ/WRITE flag support for export
>   - Rework the commit message
>
> v7 (Jason Ekstrand):
>   - Require at least one sync flag
>   - Fix a refcounting bug: dma_resv_get_excl() doesn't take a reference
>   - Use _rcu helpers since we're accessing the dma_resv read-only
>
> v8 (Jason Ekstrand):
>   - Return -ENOMEM if the sync_file_create fails
>   - Predicate support on IS_ENABLED(CONFIG_SYNC_FILE)
>
> v9 (Jason Ekstrand):
>   - Add documentation for the new ioctl
>
> v10 (Jason Ekstrand):
>   - Go back to dma_buf_sync_file as the ioctl struct name
>
> v11 (Daniel Vetter):
>   - Go back to dma_buf_export_sync_file as the ioctl struct name
>   - Better kerneldoc describing what the read/write flags do
>
> v12 (Christian König):
>   - Document why we chose to make it an ioctl on dma-buf
>
> v13 (Jason Ekstrand):
>   - Rebase on Christian König's fence rework
>
> v14 (Daniel Vetter & Christian König):
>   - Use dma_rev_usage_rw to get the properly inverted usage to pass to
>     dma_resv_get_singleton()
>   - Clean up the sync_file and fd if copy_to_user() fails
>
> Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
> Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
> Signed-off-by: Jason Ekstrand <jason.ekstrand@collabora.com>
> Acked-by: Simon Ser <contact@emersion.fr>
> Acked-by: Christian König <christian.koenig@amd.com>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Sumit Semwal <sumit.semwal@linaro.org>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> ---
>   drivers/dma-buf/dma-buf.c    | 67 ++++++++++++++++++++++++++++++++++++
>   include/uapi/linux/dma-buf.h | 35 +++++++++++++++++++
>   2 files changed, 102 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 79795857be3e..6ff54f7e6119 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -20,6 +20,7 @@
>   #include <linux/debugfs.h>
>   #include <linux/module.h>
>   #include <linux/seq_file.h>
> +#include <linux/sync_file.h>
>   #include <linux/poll.h>
>   #include <linux/dma-resv.h>
>   #include <linux/mm.h>
> @@ -192,6 +193,9 @@ static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
>    * Note that this only signals the completion of the respective fences, i.e. the
>    * DMA transfers are complete. Cache flushing and any other necessary
>    * preparations before CPU access can begin still need to happen.
> + *
> + * As an alternative to poll(), the set of fences on DMA buffer can be
> + * exported as a &sync_file using &dma_buf_sync_file_export.
>    */
>   
>   static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
> @@ -326,6 +330,64 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
>   	return 0;
>   }
>   
> +#if IS_ENABLED(CONFIG_SYNC_FILE)
> +static long dma_buf_export_sync_file(struct dma_buf *dmabuf,
> +				     void __user *user_data)
> +{
> +	struct dma_buf_export_sync_file arg;
> +	enum dma_resv_usage usage;
> +	struct dma_fence *fence = NULL;
> +	struct sync_file *sync_file;
> +	int fd, ret;
> +
> +	if (copy_from_user(&arg, user_data, sizeof(arg)))
> +		return -EFAULT;
> +
> +	if (arg.flags & ~DMA_BUF_SYNC_RW)
> +		return -EINVAL;
> +
> +	if ((arg.flags & DMA_BUF_SYNC_RW) == 0)
> +		return -EINVAL;
> +
> +	fd = get_unused_fd_flags(O_CLOEXEC);
> +	if (fd < 0)
> +		return fd;
> +
> +	usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
> +	ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
> +	if (ret)
> +		goto err_put_fd;
> +
> +	if (!fence)
> +		fence = dma_fence_get_stub();
> +
> +	sync_file = sync_file_create(fence);
> +
> +	dma_fence_put(fence);
> +
> +	if (!sync_file) {
> +		ret = -ENOMEM;
> +		goto err_put_fd;
> +	}
> +
> +	arg.fd = fd;
> +	if (copy_to_user(user_data, &arg, sizeof(arg))) {
> +		ret = -EFAULT;
> +		goto err_put_file;
> +	}
> +
> +	fd_install(fd, sync_file->file);
> +
> +	return 0;
> +
> +err_put_file:
> +	fput(sync_file->file);
> +err_put_fd:
> +	put_unused_fd(fd);
> +	return ret;
> +}
> +#endif
> +
>   static long dma_buf_ioctl(struct file *file,
>   			  unsigned int cmd, unsigned long arg)
>   {
> @@ -369,6 +431,11 @@ static long dma_buf_ioctl(struct file *file,
>   	case DMA_BUF_SET_NAME_B:
>   		return dma_buf_set_name(dmabuf, (const char __user *)arg);
>   
> +#if IS_ENABLED(CONFIG_SYNC_FILE)
> +	case DMA_BUF_IOCTL_EXPORT_SYNC_FILE:
> +		return dma_buf_export_sync_file(dmabuf, (void __user *)arg);
> +#endif
> +
>   	default:
>   		return -ENOTTY;
>   	}
> diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h
> index 8e4a2ca0bcbf..46f1e3e98b02 100644
> --- a/include/uapi/linux/dma-buf.h
> +++ b/include/uapi/linux/dma-buf.h
> @@ -85,6 +85,40 @@ struct dma_buf_sync {
>   
>   #define DMA_BUF_NAME_LEN	32
>   
> +/**
> + * struct dma_buf_export_sync_file - Get a sync_file from a dma-buf
> + *
> + * Userspace can perform a DMA_BUF_IOCTL_EXPORT_SYNC_FILE to retrieve the
> + * current set of fences on a dma-buf file descriptor as a sync_file.  CPU
> + * waits via poll() or other driver-specific mechanisms typically wait on
> + * whatever fences are on the dma-buf at the time the wait begins.  This
> + * is similar except that it takes a snapshot of the current fences on the
> + * dma-buf for waiting later instead of waiting immediately.  This is
> + * useful for modern graphics APIs such as Vulkan which assume an explicit
> + * synchronization model but still need to inter-operate with dma-buf.
> + */
> +struct dma_buf_export_sync_file {
> +	/**
> +	 * @flags: Read/write flags
> +	 *
> +	 * Must be DMA_BUF_SYNC_READ, DMA_BUF_SYNC_WRITE, or both.
> +	 *
> +	 * If DMA_BUF_SYNC_READ is set and DMA_BUF_SYNC_WRITE is not set,
> +	 * the returned sync file waits on any writers of the dma-buf to
> +	 * complete.  Waiting on the returned sync file is equivalent to
> +	 * poll() with POLLIN.
> +	 *
> +	 * If DMA_BUF_SYNC_WRITE is set, the returned sync file waits on
> +	 * any users of the dma-buf (read or write) to complete.  Waiting
> +	 * on the returned sync file is equivalent to poll() with POLLOUT.
> +	 * If both DMA_BUF_SYNC_WRITE and DMA_BUF_SYNC_READ are set, this
> +	 * is equivalent to just DMA_BUF_SYNC_WRITE.
> +	 */
> +	__u32 flags;
> +	/** @fd: Returned sync file descriptor */
> +	__s32 fd;
> +};
> +
>   #define DMA_BUF_BASE		'b'
>   #define DMA_BUF_IOCTL_SYNC	_IOW(DMA_BUF_BASE, 0, struct dma_buf_sync)
>   
> @@ -94,5 +128,6 @@ struct dma_buf_sync {
>   #define DMA_BUF_SET_NAME	_IOW(DMA_BUF_BASE, 1, const char *)
>   #define DMA_BUF_SET_NAME_A	_IOW(DMA_BUF_BASE, 1, u32)
>   #define DMA_BUF_SET_NAME_B	_IOW(DMA_BUF_BASE, 1, u64)
> +#define DMA_BUF_IOCTL_EXPORT_SYNC_FILE	_IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file)
>   
>   #endif

Re: [PATCH 0/2] dma-buf: Add an API for exporting sync files (v14)

[Daniel Stone]

On Sat, 7 May 2022 at 14:18, Jason Ekstrand <jason@jlekstrand.net> wrote:
> This patch series actually contains two new ioctls.  There is the export one
> mentioned above as well as an RFC for an import ioctl which provides the other
> half.  The intention is to land the export ioctl since it seems like there's
> no real disagreement on that one.  The import ioctl, however, has a lot of
> debate around it so it's intended to be RFC-only for now.

Errr, I think we're good with this one now right?

From the uAPI point of view, having looked through the Mesa MR, both are:
Acked-by: Daniel Stone <daniels@collabora.com>

Cheers,
Daniel

Re: [PATCH 1/2] dma-buf: Add an API for exporting sync files (v14)

[Daniel Vetter]

On Mon, May 09, 2022 at 07:54:19AM +0200, Christian König wrote:
> Reviewed-by: Christian König <christian.koenig@amd.com> for the series.
> 
> I assume you have the userspace part ready as well? If yes let's push this
> to drm-misc-next asap.

Hopefully I'm not too late, but I think all my review has also been
addressed. On the series:

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> 
> Christian.
> 
> Am 06.05.22 um 20:02 schrieb Jason Ekstrand:
> > Modern userspace APIs like Vulkan are built on an explicit
> > synchronization model.  This doesn't always play nicely with the
> > implicit synchronization used in the kernel and assumed by X11 and
> > Wayland.  The client -> compositor half of the synchronization isn't too
> > bad, at least on intel, because we can control whether or not i915
> > synchronizes on the buffer and whether or not it's considered written.
> > 
> > The harder part is the compositor -> client synchronization when we get
> > the buffer back from the compositor.  We're required to be able to
> > provide the client with a VkSemaphore and VkFence representing the point
> > in time where the window system (compositor and/or display) finished
> > using the buffer.  With current APIs, it's very hard to do this in such
> > a way that we don't get confused by the Vulkan driver's access of the
> > buffer.  In particular, once we tell the kernel that we're rendering to
> > the buffer again, any CPU waits on the buffer or GPU dependencies will
> > wait on some of the client rendering and not just the compositor.
> > 
> > This new IOCTL solves this problem by allowing us to get a snapshot of
> > the implicit synchronization state of a given dma-buf in the form of a
> > sync file.  It's effectively the same as a poll() or I915_GEM_WAIT only,
> > instead of CPU waiting directly, it encapsulates the wait operation, at
> > the current moment in time, in a sync_file so we can check/wait on it
> > later.  As long as the Vulkan driver does the sync_file export from the
> > dma-buf before we re-introduce it for rendering, it will only contain
> > fences from the compositor or display.  This allows to accurately turn
> > it into a VkFence or VkSemaphore without any over-synchronization.
> > 
> > By making this an ioctl on the dma-buf itself, it allows this new
> > functionality to be used in an entirely driver-agnostic way without
> > having access to a DRM fd. This makes it ideal for use in driver-generic
> > code in Mesa or in a client such as a compositor where the DRM fd may be
> > hard to reach.
> > 
> > v2 (Jason Ekstrand):
> >   - Use a wrapper dma_fence_array of all fences including the new one
> >     when importing an exclusive fence.
> > 
> > v3 (Jason Ekstrand):
> >   - Lock around setting shared fences as well as exclusive
> >   - Mark SIGNAL_SYNC_FILE as a read-write ioctl.
> >   - Initialize ret to 0 in dma_buf_wait_sync_file
> > 
> > v4 (Jason Ekstrand):
> >   - Use the new dma_resv_get_singleton helper
> > 
> > v5 (Jason Ekstrand):
> >   - Rename the IOCTLs to import/export rather than wait/signal
> >   - Drop the WRITE flag and always get/set the exclusive fence
> > 
> > v6 (Jason Ekstrand):
> >   - Drop the sync_file import as it was all-around sketchy and not nearly
> >     as useful as import.
> >   - Re-introduce READ/WRITE flag support for export
> >   - Rework the commit message
> > 
> > v7 (Jason Ekstrand):
> >   - Require at least one sync flag
> >   - Fix a refcounting bug: dma_resv_get_excl() doesn't take a reference
> >   - Use _rcu helpers since we're accessing the dma_resv read-only
> > 
> > v8 (Jason Ekstrand):
> >   - Return -ENOMEM if the sync_file_create fails
> >   - Predicate support on IS_ENABLED(CONFIG_SYNC_FILE)
> > 
> > v9 (Jason Ekstrand):
> >   - Add documentation for the new ioctl
> > 
> > v10 (Jason Ekstrand):
> >   - Go back to dma_buf_sync_file as the ioctl struct name
> > 
> > v11 (Daniel Vetter):
> >   - Go back to dma_buf_export_sync_file as the ioctl struct name
> >   - Better kerneldoc describing what the read/write flags do
> > 
> > v12 (Christian König):
> >   - Document why we chose to make it an ioctl on dma-buf
> > 
> > v13 (Jason Ekstrand):
> >   - Rebase on Christian König's fence rework
> > 
> > v14 (Daniel Vetter & Christian König):
> >   - Use dma_rev_usage_rw to get the properly inverted usage to pass to
> >     dma_resv_get_singleton()
> >   - Clean up the sync_file and fd if copy_to_user() fails
> > 
> > Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
> > Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
> > Signed-off-by: Jason Ekstrand <jason.ekstrand@collabora.com>
> > Acked-by: Simon Ser <contact@emersion.fr>
> > Acked-by: Christian König <christian.koenig@amd.com>
> > Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Cc: Sumit Semwal <sumit.semwal@linaro.org>
> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > ---
> >   drivers/dma-buf/dma-buf.c    | 67 ++++++++++++++++++++++++++++++++++++
> >   include/uapi/linux/dma-buf.h | 35 +++++++++++++++++++
> >   2 files changed, 102 insertions(+)
> > 
> > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > index 79795857be3e..6ff54f7e6119 100644
> > --- a/drivers/dma-buf/dma-buf.c
> > +++ b/drivers/dma-buf/dma-buf.c
> > @@ -20,6 +20,7 @@
> >   #include <linux/debugfs.h>
> >   #include <linux/module.h>
> >   #include <linux/seq_file.h>
> > +#include <linux/sync_file.h>
> >   #include <linux/poll.h>
> >   #include <linux/dma-resv.h>
> >   #include <linux/mm.h>
> > @@ -192,6 +193,9 @@ static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
> >    * Note that this only signals the completion of the respective fences, i.e. the
> >    * DMA transfers are complete. Cache flushing and any other necessary
> >    * preparations before CPU access can begin still need to happen.
> > + *
> > + * As an alternative to poll(), the set of fences on DMA buffer can be
> > + * exported as a &sync_file using &dma_buf_sync_file_export.
> >    */
> >   static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
> > @@ -326,6 +330,64 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
> >   	return 0;
> >   }
> > +#if IS_ENABLED(CONFIG_SYNC_FILE)
> > +static long dma_buf_export_sync_file(struct dma_buf *dmabuf,
> > +				     void __user *user_data)
> > +{
> > +	struct dma_buf_export_sync_file arg;
> > +	enum dma_resv_usage usage;
> > +	struct dma_fence *fence = NULL;
> > +	struct sync_file *sync_file;
> > +	int fd, ret;
> > +
> > +	if (copy_from_user(&arg, user_data, sizeof(arg)))
> > +		return -EFAULT;
> > +
> > +	if (arg.flags & ~DMA_BUF_SYNC_RW)
> > +		return -EINVAL;
> > +
> > +	if ((arg.flags & DMA_BUF_SYNC_RW) == 0)
> > +		return -EINVAL;
> > +
> > +	fd = get_unused_fd_flags(O_CLOEXEC);
> > +	if (fd < 0)
> > +		return fd;
> > +
> > +	usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
> > +	ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
> > +	if (ret)
> > +		goto err_put_fd;
> > +
> > +	if (!fence)
> > +		fence = dma_fence_get_stub();
> > +
> > +	sync_file = sync_file_create(fence);
> > +
> > +	dma_fence_put(fence);
> > +
> > +	if (!sync_file) {
> > +		ret = -ENOMEM;
> > +		goto err_put_fd;
> > +	}
> > +
> > +	arg.fd = fd;
> > +	if (copy_to_user(user_data, &arg, sizeof(arg))) {
> > +		ret = -EFAULT;
> > +		goto err_put_file;
> > +	}
> > +
> > +	fd_install(fd, sync_file->file);
> > +
> > +	return 0;
> > +
> > +err_put_file:
> > +	fput(sync_file->file);
> > +err_put_fd:
> > +	put_unused_fd(fd);
> > +	return ret;
> > +}
> > +#endif
> > +
> >   static long dma_buf_ioctl(struct file *file,
> >   			  unsigned int cmd, unsigned long arg)
> >   {
> > @@ -369,6 +431,11 @@ static long dma_buf_ioctl(struct file *file,
> >   	case DMA_BUF_SET_NAME_B:
> >   		return dma_buf_set_name(dmabuf, (const char __user *)arg);
> > +#if IS_ENABLED(CONFIG_SYNC_FILE)
> > +	case DMA_BUF_IOCTL_EXPORT_SYNC_FILE:
> > +		return dma_buf_export_sync_file(dmabuf, (void __user *)arg);
> > +#endif
> > +
> >   	default:
> >   		return -ENOTTY;
> >   	}
> > diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h
> > index 8e4a2ca0bcbf..46f1e3e98b02 100644
> > --- a/include/uapi/linux/dma-buf.h
> > +++ b/include/uapi/linux/dma-buf.h
> > @@ -85,6 +85,40 @@ struct dma_buf_sync {
> >   #define DMA_BUF_NAME_LEN	32
> > +/**
> > + * struct dma_buf_export_sync_file - Get a sync_file from a dma-buf
> > + *
> > + * Userspace can perform a DMA_BUF_IOCTL_EXPORT_SYNC_FILE to retrieve the
> > + * current set of fences on a dma-buf file descriptor as a sync_file.  CPU
> > + * waits via poll() or other driver-specific mechanisms typically wait on
> > + * whatever fences are on the dma-buf at the time the wait begins.  This
> > + * is similar except that it takes a snapshot of the current fences on the
> > + * dma-buf for waiting later instead of waiting immediately.  This is
> > + * useful for modern graphics APIs such as Vulkan which assume an explicit
> > + * synchronization model but still need to inter-operate with dma-buf.
> > + */
> > +struct dma_buf_export_sync_file {
> > +	/**
> > +	 * @flags: Read/write flags
> > +	 *
> > +	 * Must be DMA_BUF_SYNC_READ, DMA_BUF_SYNC_WRITE, or both.
> > +	 *
> > +	 * If DMA_BUF_SYNC_READ is set and DMA_BUF_SYNC_WRITE is not set,
> > +	 * the returned sync file waits on any writers of the dma-buf to
> > +	 * complete.  Waiting on the returned sync file is equivalent to
> > +	 * poll() with POLLIN.
> > +	 *
> > +	 * If DMA_BUF_SYNC_WRITE is set, the returned sync file waits on
> > +	 * any users of the dma-buf (read or write) to complete.  Waiting
> > +	 * on the returned sync file is equivalent to poll() with POLLOUT.
> > +	 * If both DMA_BUF_SYNC_WRITE and DMA_BUF_SYNC_READ are set, this
> > +	 * is equivalent to just DMA_BUF_SYNC_WRITE.
> > +	 */
> > +	__u32 flags;
> > +	/** @fd: Returned sync file descriptor */
> > +	__s32 fd;
> > +};
> > +
> >   #define DMA_BUF_BASE		'b'
> >   #define DMA_BUF_IOCTL_SYNC	_IOW(DMA_BUF_BASE, 0, struct dma_buf_sync)
> > @@ -94,5 +128,6 @@ struct dma_buf_sync {
> >   #define DMA_BUF_SET_NAME	_IOW(DMA_BUF_BASE, 1, const char *)
> >   #define DMA_BUF_SET_NAME_A	_IOW(DMA_BUF_BASE, 1, u32)
> >   #define DMA_BUF_SET_NAME_B	_IOW(DMA_BUF_BASE, 1, u64)
> > +#define DMA_BUF_IOCTL_EXPORT_SYNC_FILE	_IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file)
> >   #endif
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH 0/2] dma-buf: Add an API for exporting sync files (v14)

[Jason Ekstrand]

[-- Attachment #1: Type: text/plain, Size: 1214 bytes --]

On Wed, May 25, 2022 at 5:02 AM Daniel Stone <daniel@fooishbar.org> wrote:

> On Sat, 7 May 2022 at 14:18, Jason Ekstrand <jason@jlekstrand.net> wrote:
> > This patch series actually contains two new ioctls.  There is the export
> one
> > mentioned above as well as an RFC for an import ioctl which provides the
> other
> > half.  The intention is to land the export ioctl since it seems like
> there's
> > no real disagreement on that one.  The import ioctl, however, has a lot
> of
> > debate around it so it's intended to be RFC-only for now.
>
> Errr, I think we're good with this one now right?
>

Yeah, I dropped the RFC from the patch, just not the description in the
cover letter, apparently.


> From the uAPI point of view, having looked through the Mesa MR, both are:
> Acked-by: Daniel Stone <daniels@collabora.com>
>

For reference:
https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4037

Yes, I agree it's gotten sufficient review at this point that I think we
can call the uAPI reviewed.  I'm good with landing now.  Sorry that took so
long but the original version I had only used half of the new API and I
wanted to make sure both halves got good testing.

--Jason



> Cheers,
> Daniel
>

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Re: [PATCH 1/2] dma-buf: Add an API for exporting sync files (v14)

[Jason Ekstrand]

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On Wed, May 25, 2022 at 8:20 AM Daniel Vetter <daniel@ffwll.ch> wrote:

> On Mon, May 09, 2022 at 07:54:19AM +0200, Christian König wrote:
> > Reviewed-by: Christian König <christian.koenig@amd.com> for the series.
> >
> > I assume you have the userspace part ready as well? If yes let's push
> this
> > to drm-misc-next asap.
>
> Hopefully I'm not too late, but I think all my review has also been
> addressed. On the series:
>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>

Thanks!  If Christian hasn't already, can we get this in drm-misc-next
please?  I don't have access AFAIK.

--Jason



> >
> > Christian.
> >
> > Am 06.05.22 um 20:02 schrieb Jason Ekstrand:
> > > Modern userspace APIs like Vulkan are built on an explicit
> > > synchronization model.  This doesn't always play nicely with the
> > > implicit synchronization used in the kernel and assumed by X11 and
> > > Wayland.  The client -> compositor half of the synchronization isn't
> too
> > > bad, at least on intel, because we can control whether or not i915
> > > synchronizes on the buffer and whether or not it's considered written.
> > >
> > > The harder part is the compositor -> client synchronization when we get
> > > the buffer back from the compositor.  We're required to be able to
> > > provide the client with a VkSemaphore and VkFence representing the
> point
> > > in time where the window system (compositor and/or display) finished
> > > using the buffer.  With current APIs, it's very hard to do this in such
> > > a way that we don't get confused by the Vulkan driver's access of the
> > > buffer.  In particular, once we tell the kernel that we're rendering to
> > > the buffer again, any CPU waits on the buffer or GPU dependencies will
> > > wait on some of the client rendering and not just the compositor.
> > >
> > > This new IOCTL solves this problem by allowing us to get a snapshot of
> > > the implicit synchronization state of a given dma-buf in the form of a
> > > sync file.  It's effectively the same as a poll() or I915_GEM_WAIT
> only,
> > > instead of CPU waiting directly, it encapsulates the wait operation, at
> > > the current moment in time, in a sync_file so we can check/wait on it
> > > later.  As long as the Vulkan driver does the sync_file export from the
> > > dma-buf before we re-introduce it for rendering, it will only contain
> > > fences from the compositor or display.  This allows to accurately turn
> > > it into a VkFence or VkSemaphore without any over-synchronization.
> > >
> > > By making this an ioctl on the dma-buf itself, it allows this new
> > > functionality to be used in an entirely driver-agnostic way without
> > > having access to a DRM fd. This makes it ideal for use in
> driver-generic
> > > code in Mesa or in a client such as a compositor where the DRM fd may
> be
> > > hard to reach.
> > >
> > > v2 (Jason Ekstrand):
> > >   - Use a wrapper dma_fence_array of all fences including the new one
> > >     when importing an exclusive fence.
> > >
> > > v3 (Jason Ekstrand):
> > >   - Lock around setting shared fences as well as exclusive
> > >   - Mark SIGNAL_SYNC_FILE as a read-write ioctl.
> > >   - Initialize ret to 0 in dma_buf_wait_sync_file
> > >
> > > v4 (Jason Ekstrand):
> > >   - Use the new dma_resv_get_singleton helper
> > >
> > > v5 (Jason Ekstrand):
> > >   - Rename the IOCTLs to import/export rather than wait/signal
> > >   - Drop the WRITE flag and always get/set the exclusive fence
> > >
> > > v6 (Jason Ekstrand):
> > >   - Drop the sync_file import as it was all-around sketchy and not
> nearly
> > >     as useful as import.
> > >   - Re-introduce READ/WRITE flag support for export
> > >   - Rework the commit message
> > >
> > > v7 (Jason Ekstrand):
> > >   - Require at least one sync flag
> > >   - Fix a refcounting bug: dma_resv_get_excl() doesn't take a reference
> > >   - Use _rcu helpers since we're accessing the dma_resv read-only
> > >
> > > v8 (Jason Ekstrand):
> > >   - Return -ENOMEM if the sync_file_create fails
> > >   - Predicate support on IS_ENABLED(CONFIG_SYNC_FILE)
> > >
> > > v9 (Jason Ekstrand):
> > >   - Add documentation for the new ioctl
> > >
> > > v10 (Jason Ekstrand):
> > >   - Go back to dma_buf_sync_file as the ioctl struct name
> > >
> > > v11 (Daniel Vetter):
> > >   - Go back to dma_buf_export_sync_file as the ioctl struct name
> > >   - Better kerneldoc describing what the read/write flags do
> > >
> > > v12 (Christian König):
> > >   - Document why we chose to make it an ioctl on dma-buf
> > >
> > > v13 (Jason Ekstrand):
> > >   - Rebase on Christian König's fence rework
> > >
> > > v14 (Daniel Vetter & Christian König):
> > >   - Use dma_rev_usage_rw to get the properly inverted usage to pass to
> > >     dma_resv_get_singleton()
> > >   - Clean up the sync_file and fd if copy_to_user() fails
> > >
> > > Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
> > > Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
> > > Signed-off-by: Jason Ekstrand <jason.ekstrand@collabora.com>
> > > Acked-by: Simon Ser <contact@emersion.fr>
> > > Acked-by: Christian König <christian.koenig@amd.com>
> > > Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > Cc: Sumit Semwal <sumit.semwal@linaro.org>
> > > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > > ---
> > >   drivers/dma-buf/dma-buf.c    | 67
> ++++++++++++++++++++++++++++++++++++
> > >   include/uapi/linux/dma-buf.h | 35 +++++++++++++++++++
> > >   2 files changed, 102 insertions(+)
> > >
> > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > > index 79795857be3e..6ff54f7e6119 100644
> > > --- a/drivers/dma-buf/dma-buf.c
> > > +++ b/drivers/dma-buf/dma-buf.c
> > > @@ -20,6 +20,7 @@
> > >   #include <linux/debugfs.h>
> > >   #include <linux/module.h>
> > >   #include <linux/seq_file.h>
> > > +#include <linux/sync_file.h>
> > >   #include <linux/poll.h>
> > >   #include <linux/dma-resv.h>
> > >   #include <linux/mm.h>
> > > @@ -192,6 +193,9 @@ static loff_t dma_buf_llseek(struct file *file,
> loff_t offset, int whence)
> > >    * Note that this only signals the completion of the respective
> fences, i.e. the
> > >    * DMA transfers are complete. Cache flushing and any other necessary
> > >    * preparations before CPU access can begin still need to happen.
> > > + *
> > > + * As an alternative to poll(), the set of fences on DMA buffer can be
> > > + * exported as a &sync_file using &dma_buf_sync_file_export.
> > >    */
> > >   static void dma_buf_poll_cb(struct dma_fence *fence, struct
> dma_fence_cb *cb)
> > > @@ -326,6 +330,64 @@ static long dma_buf_set_name(struct dma_buf
> *dmabuf, const char __user *buf)
> > >     return 0;
> > >   }
> > > +#if IS_ENABLED(CONFIG_SYNC_FILE)
> > > +static long dma_buf_export_sync_file(struct dma_buf *dmabuf,
> > > +                                void __user *user_data)
> > > +{
> > > +   struct dma_buf_export_sync_file arg;
> > > +   enum dma_resv_usage usage;
> > > +   struct dma_fence *fence = NULL;
> > > +   struct sync_file *sync_file;
> > > +   int fd, ret;
> > > +
> > > +   if (copy_from_user(&arg, user_data, sizeof(arg)))
> > > +           return -EFAULT;
> > > +
> > > +   if (arg.flags & ~DMA_BUF_SYNC_RW)
> > > +           return -EINVAL;
> > > +
> > > +   if ((arg.flags & DMA_BUF_SYNC_RW) == 0)
> > > +           return -EINVAL;
> > > +
> > > +   fd = get_unused_fd_flags(O_CLOEXEC);
> > > +   if (fd < 0)
> > > +           return fd;
> > > +
> > > +   usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
> > > +   ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
> > > +   if (ret)
> > > +           goto err_put_fd;
> > > +
> > > +   if (!fence)
> > > +           fence = dma_fence_get_stub();
> > > +
> > > +   sync_file = sync_file_create(fence);
> > > +
> > > +   dma_fence_put(fence);
> > > +
> > > +   if (!sync_file) {
> > > +           ret = -ENOMEM;
> > > +           goto err_put_fd;
> > > +   }
> > > +
> > > +   arg.fd = fd;
> > > +   if (copy_to_user(user_data, &arg, sizeof(arg))) {
> > > +           ret = -EFAULT;
> > > +           goto err_put_file;
> > > +   }
> > > +
> > > +   fd_install(fd, sync_file->file);
> > > +
> > > +   return 0;
> > > +
> > > +err_put_file:
> > > +   fput(sync_file->file);
> > > +err_put_fd:
> > > +   put_unused_fd(fd);
> > > +   return ret;
> > > +}
> > > +#endif
> > > +
> > >   static long dma_buf_ioctl(struct file *file,
> > >                       unsigned int cmd, unsigned long arg)
> > >   {
> > > @@ -369,6 +431,11 @@ static long dma_buf_ioctl(struct file *file,
> > >     case DMA_BUF_SET_NAME_B:
> > >             return dma_buf_set_name(dmabuf, (const char __user *)arg);
> > > +#if IS_ENABLED(CONFIG_SYNC_FILE)
> > > +   case DMA_BUF_IOCTL_EXPORT_SYNC_FILE:
> > > +           return dma_buf_export_sync_file(dmabuf, (void __user
> *)arg);
> > > +#endif
> > > +
> > >     default:
> > >             return -ENOTTY;
> > >     }
> > > diff --git a/include/uapi/linux/dma-buf.h
> b/include/uapi/linux/dma-buf.h
> > > index 8e4a2ca0bcbf..46f1e3e98b02 100644
> > > --- a/include/uapi/linux/dma-buf.h
> > > +++ b/include/uapi/linux/dma-buf.h
> > > @@ -85,6 +85,40 @@ struct dma_buf_sync {
> > >   #define DMA_BUF_NAME_LEN  32
> > > +/**
> > > + * struct dma_buf_export_sync_file - Get a sync_file from a dma-buf
> > > + *
> > > + * Userspace can perform a DMA_BUF_IOCTL_EXPORT_SYNC_FILE to retrieve
> the
> > > + * current set of fences on a dma-buf file descriptor as a
> sync_file.  CPU
> > > + * waits via poll() or other driver-specific mechanisms typically
> wait on
> > > + * whatever fences are on the dma-buf at the time the wait begins.
> This
> > > + * is similar except that it takes a snapshot of the current fences
> on the
> > > + * dma-buf for waiting later instead of waiting immediately.  This is
> > > + * useful for modern graphics APIs such as Vulkan which assume an
> explicit
> > > + * synchronization model but still need to inter-operate with dma-buf.
> > > + */
> > > +struct dma_buf_export_sync_file {
> > > +   /**
> > > +    * @flags: Read/write flags
> > > +    *
> > > +    * Must be DMA_BUF_SYNC_READ, DMA_BUF_SYNC_WRITE, or both.
> > > +    *
> > > +    * If DMA_BUF_SYNC_READ is set and DMA_BUF_SYNC_WRITE is not set,
> > > +    * the returned sync file waits on any writers of the dma-buf to
> > > +    * complete.  Waiting on the returned sync file is equivalent to
> > > +    * poll() with POLLIN.
> > > +    *
> > > +    * If DMA_BUF_SYNC_WRITE is set, the returned sync file waits on
> > > +    * any users of the dma-buf (read or write) to complete.  Waiting
> > > +    * on the returned sync file is equivalent to poll() with POLLOUT.
> > > +    * If both DMA_BUF_SYNC_WRITE and DMA_BUF_SYNC_READ are set, this
> > > +    * is equivalent to just DMA_BUF_SYNC_WRITE.
> > > +    */
> > > +   __u32 flags;
> > > +   /** @fd: Returned sync file descriptor */
> > > +   __s32 fd;
> > > +};
> > > +
> > >   #define DMA_BUF_BASE              'b'
> > >   #define DMA_BUF_IOCTL_SYNC        _IOW(DMA_BUF_BASE, 0, struct
> dma_buf_sync)
> > > @@ -94,5 +128,6 @@ struct dma_buf_sync {
> > >   #define DMA_BUF_SET_NAME  _IOW(DMA_BUF_BASE, 1, const char *)
> > >   #define DMA_BUF_SET_NAME_A        _IOW(DMA_BUF_BASE, 1, u32)
> > >   #define DMA_BUF_SET_NAME_B        _IOW(DMA_BUF_BASE, 1, u64)
> > > +#define DMA_BUF_IOCTL_EXPORT_SYNC_FILE     _IOWR(DMA_BUF_BASE, 2,
> struct dma_buf_export_sync_file)
> > >   #endif
> >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
>

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Re: [PATCH 1/2] dma-buf: Add an API for exporting sync files (v14)

[Daniel Vetter]

On Wed, May 25, 2022 at 10:35:47AM -0500, Jason Ekstrand wrote:
> On Wed, May 25, 2022 at 8:20 AM Daniel Vetter <daniel@ffwll.ch> wrote:
> 
> > On Mon, May 09, 2022 at 07:54:19AM +0200, Christian König wrote:
> > > Reviewed-by: Christian König <christian.koenig@amd.com> for the series.
> > >
> > > I assume you have the userspace part ready as well? If yes let's push
> > this
> > > to drm-misc-next asap.
> >
> > Hopefully I'm not too late, but I think all my review has also been
> > addressed. On the series:
> >
> > Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> >
> 
> Thanks!  If Christian hasn't already, can we get this in drm-misc-next
> please?  I don't have access AFAIK.

We need to fix this?
-Daniel
> 
> --Jason
> 
> 
> 
> > >
> > > Christian.
> > >
> > > Am 06.05.22 um 20:02 schrieb Jason Ekstrand:
> > > > Modern userspace APIs like Vulkan are built on an explicit
> > > > synchronization model.  This doesn't always play nicely with the
> > > > implicit synchronization used in the kernel and assumed by X11 and
> > > > Wayland.  The client -> compositor half of the synchronization isn't
> > too
> > > > bad, at least on intel, because we can control whether or not i915
> > > > synchronizes on the buffer and whether or not it's considered written.
> > > >
> > > > The harder part is the compositor -> client synchronization when we get
> > > > the buffer back from the compositor.  We're required to be able to
> > > > provide the client with a VkSemaphore and VkFence representing the
> > point
> > > > in time where the window system (compositor and/or display) finished
> > > > using the buffer.  With current APIs, it's very hard to do this in such
> > > > a way that we don't get confused by the Vulkan driver's access of the
> > > > buffer.  In particular, once we tell the kernel that we're rendering to
> > > > the buffer again, any CPU waits on the buffer or GPU dependencies will
> > > > wait on some of the client rendering and not just the compositor.
> > > >
> > > > This new IOCTL solves this problem by allowing us to get a snapshot of
> > > > the implicit synchronization state of a given dma-buf in the form of a
> > > > sync file.  It's effectively the same as a poll() or I915_GEM_WAIT
> > only,
> > > > instead of CPU waiting directly, it encapsulates the wait operation, at
> > > > the current moment in time, in a sync_file so we can check/wait on it
> > > > later.  As long as the Vulkan driver does the sync_file export from the
> > > > dma-buf before we re-introduce it for rendering, it will only contain
> > > > fences from the compositor or display.  This allows to accurately turn
> > > > it into a VkFence or VkSemaphore without any over-synchronization.
> > > >
> > > > By making this an ioctl on the dma-buf itself, it allows this new
> > > > functionality to be used in an entirely driver-agnostic way without
> > > > having access to a DRM fd. This makes it ideal for use in
> > driver-generic
> > > > code in Mesa or in a client such as a compositor where the DRM fd may
> > be
> > > > hard to reach.
> > > >
> > > > v2 (Jason Ekstrand):
> > > >   - Use a wrapper dma_fence_array of all fences including the new one
> > > >     when importing an exclusive fence.
> > > >
> > > > v3 (Jason Ekstrand):
> > > >   - Lock around setting shared fences as well as exclusive
> > > >   - Mark SIGNAL_SYNC_FILE as a read-write ioctl.
> > > >   - Initialize ret to 0 in dma_buf_wait_sync_file
> > > >
> > > > v4 (Jason Ekstrand):
> > > >   - Use the new dma_resv_get_singleton helper
> > > >
> > > > v5 (Jason Ekstrand):
> > > >   - Rename the IOCTLs to import/export rather than wait/signal
> > > >   - Drop the WRITE flag and always get/set the exclusive fence
> > > >
> > > > v6 (Jason Ekstrand):
> > > >   - Drop the sync_file import as it was all-around sketchy and not
> > nearly
> > > >     as useful as import.
> > > >   - Re-introduce READ/WRITE flag support for export
> > > >   - Rework the commit message
> > > >
> > > > v7 (Jason Ekstrand):
> > > >   - Require at least one sync flag
> > > >   - Fix a refcounting bug: dma_resv_get_excl() doesn't take a reference
> > > >   - Use _rcu helpers since we're accessing the dma_resv read-only
> > > >
> > > > v8 (Jason Ekstrand):
> > > >   - Return -ENOMEM if the sync_file_create fails
> > > >   - Predicate support on IS_ENABLED(CONFIG_SYNC_FILE)
> > > >
> > > > v9 (Jason Ekstrand):
> > > >   - Add documentation for the new ioctl
> > > >
> > > > v10 (Jason Ekstrand):
> > > >   - Go back to dma_buf_sync_file as the ioctl struct name
> > > >
> > > > v11 (Daniel Vetter):
> > > >   - Go back to dma_buf_export_sync_file as the ioctl struct name
> > > >   - Better kerneldoc describing what the read/write flags do
> > > >
> > > > v12 (Christian König):
> > > >   - Document why we chose to make it an ioctl on dma-buf
> > > >
> > > > v13 (Jason Ekstrand):
> > > >   - Rebase on Christian König's fence rework
> > > >
> > > > v14 (Daniel Vetter & Christian König):
> > > >   - Use dma_rev_usage_rw to get the properly inverted usage to pass to
> > > >     dma_resv_get_singleton()
> > > >   - Clean up the sync_file and fd if copy_to_user() fails
> > > >
> > > > Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
> > > > Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
> > > > Signed-off-by: Jason Ekstrand <jason.ekstrand@collabora.com>
> > > > Acked-by: Simon Ser <contact@emersion.fr>
> > > > Acked-by: Christian König <christian.koenig@amd.com>
> > > > Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > > Cc: Sumit Semwal <sumit.semwal@linaro.org>
> > > > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > > > ---
> > > >   drivers/dma-buf/dma-buf.c    | 67
> > ++++++++++++++++++++++++++++++++++++
> > > >   include/uapi/linux/dma-buf.h | 35 +++++++++++++++++++
> > > >   2 files changed, 102 insertions(+)
> > > >
> > > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > > > index 79795857be3e..6ff54f7e6119 100644
> > > > --- a/drivers/dma-buf/dma-buf.c
> > > > +++ b/drivers/dma-buf/dma-buf.c
> > > > @@ -20,6 +20,7 @@
> > > >   #include <linux/debugfs.h>
> > > >   #include <linux/module.h>
> > > >   #include <linux/seq_file.h>
> > > > +#include <linux/sync_file.h>
> > > >   #include <linux/poll.h>
> > > >   #include <linux/dma-resv.h>
> > > >   #include <linux/mm.h>
> > > > @@ -192,6 +193,9 @@ static loff_t dma_buf_llseek(struct file *file,
> > loff_t offset, int whence)
> > > >    * Note that this only signals the completion of the respective
> > fences, i.e. the
> > > >    * DMA transfers are complete. Cache flushing and any other necessary
> > > >    * preparations before CPU access can begin still need to happen.
> > > > + *
> > > > + * As an alternative to poll(), the set of fences on DMA buffer can be
> > > > + * exported as a &sync_file using &dma_buf_sync_file_export.
> > > >    */
> > > >   static void dma_buf_poll_cb(struct dma_fence *fence, struct
> > dma_fence_cb *cb)
> > > > @@ -326,6 +330,64 @@ static long dma_buf_set_name(struct dma_buf
> > *dmabuf, const char __user *buf)
> > > >     return 0;
> > > >   }
> > > > +#if IS_ENABLED(CONFIG_SYNC_FILE)
> > > > +static long dma_buf_export_sync_file(struct dma_buf *dmabuf,
> > > > +                                void __user *user_data)
> > > > +{
> > > > +   struct dma_buf_export_sync_file arg;
> > > > +   enum dma_resv_usage usage;
> > > > +   struct dma_fence *fence = NULL;
> > > > +   struct sync_file *sync_file;
> > > > +   int fd, ret;
> > > > +
> > > > +   if (copy_from_user(&arg, user_data, sizeof(arg)))
> > > > +           return -EFAULT;
> > > > +
> > > > +   if (arg.flags & ~DMA_BUF_SYNC_RW)
> > > > +           return -EINVAL;
> > > > +
> > > > +   if ((arg.flags & DMA_BUF_SYNC_RW) == 0)
> > > > +           return -EINVAL;
> > > > +
> > > > +   fd = get_unused_fd_flags(O_CLOEXEC);
> > > > +   if (fd < 0)
> > > > +           return fd;
> > > > +
> > > > +   usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
> > > > +   ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
> > > > +   if (ret)
> > > > +           goto err_put_fd;
> > > > +
> > > > +   if (!fence)
> > > > +           fence = dma_fence_get_stub();
> > > > +
> > > > +   sync_file = sync_file_create(fence);
> > > > +
> > > > +   dma_fence_put(fence);
> > > > +
> > > > +   if (!sync_file) {
> > > > +           ret = -ENOMEM;
> > > > +           goto err_put_fd;
> > > > +   }
> > > > +
> > > > +   arg.fd = fd;
> > > > +   if (copy_to_user(user_data, &arg, sizeof(arg))) {
> > > > +           ret = -EFAULT;
> > > > +           goto err_put_file;
> > > > +   }
> > > > +
> > > > +   fd_install(fd, sync_file->file);
> > > > +
> > > > +   return 0;
> > > > +
> > > > +err_put_file:
> > > > +   fput(sync_file->file);
> > > > +err_put_fd:
> > > > +   put_unused_fd(fd);
> > > > +   return ret;
> > > > +}
> > > > +#endif
> > > > +
> > > >   static long dma_buf_ioctl(struct file *file,
> > > >                       unsigned int cmd, unsigned long arg)
> > > >   {
> > > > @@ -369,6 +431,11 @@ static long dma_buf_ioctl(struct file *file,
> > > >     case DMA_BUF_SET_NAME_B:
> > > >             return dma_buf_set_name(dmabuf, (const char __user *)arg);
> > > > +#if IS_ENABLED(CONFIG_SYNC_FILE)
> > > > +   case DMA_BUF_IOCTL_EXPORT_SYNC_FILE:
> > > > +           return dma_buf_export_sync_file(dmabuf, (void __user
> > *)arg);
> > > > +#endif
> > > > +
> > > >     default:
> > > >             return -ENOTTY;
> > > >     }
> > > > diff --git a/include/uapi/linux/dma-buf.h
> > b/include/uapi/linux/dma-buf.h
> > > > index 8e4a2ca0bcbf..46f1e3e98b02 100644
> > > > --- a/include/uapi/linux/dma-buf.h
> > > > +++ b/include/uapi/linux/dma-buf.h
> > > > @@ -85,6 +85,40 @@ struct dma_buf_sync {
> > > >   #define DMA_BUF_NAME_LEN  32
> > > > +/**
> > > > + * struct dma_buf_export_sync_file - Get a sync_file from a dma-buf
> > > > + *
> > > > + * Userspace can perform a DMA_BUF_IOCTL_EXPORT_SYNC_FILE to retrieve
> > the
> > > > + * current set of fences on a dma-buf file descriptor as a
> > sync_file.  CPU
> > > > + * waits via poll() or other driver-specific mechanisms typically
> > wait on
> > > > + * whatever fences are on the dma-buf at the time the wait begins.
> > This
> > > > + * is similar except that it takes a snapshot of the current fences
> > on the
> > > > + * dma-buf for waiting later instead of waiting immediately.  This is
> > > > + * useful for modern graphics APIs such as Vulkan which assume an
> > explicit
> > > > + * synchronization model but still need to inter-operate with dma-buf.
> > > > + */
> > > > +struct dma_buf_export_sync_file {
> > > > +   /**
> > > > +    * @flags: Read/write flags
> > > > +    *
> > > > +    * Must be DMA_BUF_SYNC_READ, DMA_BUF_SYNC_WRITE, or both.
> > > > +    *
> > > > +    * If DMA_BUF_SYNC_READ is set and DMA_BUF_SYNC_WRITE is not set,
> > > > +    * the returned sync file waits on any writers of the dma-buf to
> > > > +    * complete.  Waiting on the returned sync file is equivalent to
> > > > +    * poll() with POLLIN.
> > > > +    *
> > > > +    * If DMA_BUF_SYNC_WRITE is set, the returned sync file waits on
> > > > +    * any users of the dma-buf (read or write) to complete.  Waiting
> > > > +    * on the returned sync file is equivalent to poll() with POLLOUT.
> > > > +    * If both DMA_BUF_SYNC_WRITE and DMA_BUF_SYNC_READ are set, this
> > > > +    * is equivalent to just DMA_BUF_SYNC_WRITE.
> > > > +    */
> > > > +   __u32 flags;
> > > > +   /** @fd: Returned sync file descriptor */
> > > > +   __s32 fd;
> > > > +};
> > > > +
> > > >   #define DMA_BUF_BASE              'b'
> > > >   #define DMA_BUF_IOCTL_SYNC        _IOW(DMA_BUF_BASE, 0, struct
> > dma_buf_sync)
> > > > @@ -94,5 +128,6 @@ struct dma_buf_sync {
> > > >   #define DMA_BUF_SET_NAME  _IOW(DMA_BUF_BASE, 1, const char *)
> > > >   #define DMA_BUF_SET_NAME_A        _IOW(DMA_BUF_BASE, 1, u32)
> > > >   #define DMA_BUF_SET_NAME_B        _IOW(DMA_BUF_BASE, 1, u64)
> > > > +#define DMA_BUF_IOCTL_EXPORT_SYNC_FILE     _IOWR(DMA_BUF_BASE, 2,
> > struct dma_buf_export_sync_file)
> > > >   #endif
> > >
> >
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch
> >

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH 1/2] dma-buf: Add an API for exporting sync files (v14)

[Jason Ekstrand]

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On Wed, May 25, 2022 at 10:43 AM Daniel Vetter <daniel@ffwll.ch> wrote:

> On Wed, May 25, 2022 at 10:35:47AM -0500, Jason Ekstrand wrote:
> > On Wed, May 25, 2022 at 8:20 AM Daniel Vetter <daniel@ffwll.ch> wrote:
> >
> > > On Mon, May 09, 2022 at 07:54:19AM +0200, Christian König wrote:
> > > > Reviewed-by: Christian König <christian.koenig@amd.com> for the
> series.
> > > >
> > > > I assume you have the userspace part ready as well? If yes let's push
> > > this
> > > > to drm-misc-next asap.
> > >
> > > Hopefully I'm not too late, but I think all my review has also been
> > > addressed. On the series:
> > >
> > > Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> > >
> >
> > Thanks!  If Christian hasn't already, can we get this in drm-misc-next
> > please?  I don't have access AFAIK.
>
> We need to fix this?
>

I don't do enough kernel dev to be worth giving access, I don't think.
It's infrequent enough that I'm going to have to ask someone else how to
use the tools to push stuff every time anyway.

--Jason



> -Daniel
> >
> > --Jason
> >
> >
> >
> > > >
> > > > Christian.
> > > >
> > > > Am 06.05.22 um 20:02 schrieb Jason Ekstrand:
> > > > > Modern userspace APIs like Vulkan are built on an explicit
> > > > > synchronization model.  This doesn't always play nicely with the
> > > > > implicit synchronization used in the kernel and assumed by X11 and
> > > > > Wayland.  The client -> compositor half of the synchronization
> isn't
> > > too
> > > > > bad, at least on intel, because we can control whether or not i915
> > > > > synchronizes on the buffer and whether or not it's considered
> written.
> > > > >
> > > > > The harder part is the compositor -> client synchronization when
> we get
> > > > > the buffer back from the compositor.  We're required to be able to
> > > > > provide the client with a VkSemaphore and VkFence representing the
> > > point
> > > > > in time where the window system (compositor and/or display)
> finished
> > > > > using the buffer.  With current APIs, it's very hard to do this in
> such
> > > > > a way that we don't get confused by the Vulkan driver's access of
> the
> > > > > buffer.  In particular, once we tell the kernel that we're
> rendering to
> > > > > the buffer again, any CPU waits on the buffer or GPU dependencies
> will
> > > > > wait on some of the client rendering and not just the compositor.
> > > > >
> > > > > This new IOCTL solves this problem by allowing us to get a
> snapshot of
> > > > > the implicit synchronization state of a given dma-buf in the form
> of a
> > > > > sync file.  It's effectively the same as a poll() or I915_GEM_WAIT
> > > only,
> > > > > instead of CPU waiting directly, it encapsulates the wait
> operation, at
> > > > > the current moment in time, in a sync_file so we can check/wait on
> it
> > > > > later.  As long as the Vulkan driver does the sync_file export
> from the
> > > > > dma-buf before we re-introduce it for rendering, it will only
> contain
> > > > > fences from the compositor or display.  This allows to accurately
> turn
> > > > > it into a VkFence or VkSemaphore without any over-synchronization.
> > > > >
> > > > > By making this an ioctl on the dma-buf itself, it allows this new
> > > > > functionality to be used in an entirely driver-agnostic way without
> > > > > having access to a DRM fd. This makes it ideal for use in
> > > driver-generic
> > > > > code in Mesa or in a client such as a compositor where the DRM fd
> may
> > > be
> > > > > hard to reach.
> > > > >
> > > > > v2 (Jason Ekstrand):
> > > > >   - Use a wrapper dma_fence_array of all fences including the new
> one
> > > > >     when importing an exclusive fence.
> > > > >
> > > > > v3 (Jason Ekstrand):
> > > > >   - Lock around setting shared fences as well as exclusive
> > > > >   - Mark SIGNAL_SYNC_FILE as a read-write ioctl.
> > > > >   - Initialize ret to 0 in dma_buf_wait_sync_file
> > > > >
> > > > > v4 (Jason Ekstrand):
> > > > >   - Use the new dma_resv_get_singleton helper
> > > > >
> > > > > v5 (Jason Ekstrand):
> > > > >   - Rename the IOCTLs to import/export rather than wait/signal
> > > > >   - Drop the WRITE flag and always get/set the exclusive fence
> > > > >
> > > > > v6 (Jason Ekstrand):
> > > > >   - Drop the sync_file import as it was all-around sketchy and not
> > > nearly
> > > > >     as useful as import.
> > > > >   - Re-introduce READ/WRITE flag support for export
> > > > >   - Rework the commit message
> > > > >
> > > > > v7 (Jason Ekstrand):
> > > > >   - Require at least one sync flag
> > > > >   - Fix a refcounting bug: dma_resv_get_excl() doesn't take a
> reference
> > > > >   - Use _rcu helpers since we're accessing the dma_resv read-only
> > > > >
> > > > > v8 (Jason Ekstrand):
> > > > >   - Return -ENOMEM if the sync_file_create fails
> > > > >   - Predicate support on IS_ENABLED(CONFIG_SYNC_FILE)
> > > > >
> > > > > v9 (Jason Ekstrand):
> > > > >   - Add documentation for the new ioctl
> > > > >
> > > > > v10 (Jason Ekstrand):
> > > > >   - Go back to dma_buf_sync_file as the ioctl struct name
> > > > >
> > > > > v11 (Daniel Vetter):
> > > > >   - Go back to dma_buf_export_sync_file as the ioctl struct name
> > > > >   - Better kerneldoc describing what the read/write flags do
> > > > >
> > > > > v12 (Christian König):
> > > > >   - Document why we chose to make it an ioctl on dma-buf
> > > > >
> > > > > v13 (Jason Ekstrand):
> > > > >   - Rebase on Christian König's fence rework
> > > > >
> > > > > v14 (Daniel Vetter & Christian König):
> > > > >   - Use dma_rev_usage_rw to get the properly inverted usage to
> pass to
> > > > >     dma_resv_get_singleton()
> > > > >   - Clean up the sync_file and fd if copy_to_user() fails
> > > > >
> > > > > Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
> > > > > Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
> > > > > Signed-off-by: Jason Ekstrand <jason.ekstrand@collabora.com>
> > > > > Acked-by: Simon Ser <contact@emersion.fr>
> > > > > Acked-by: Christian König <christian.koenig@amd.com>
> > > > > Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > > > Cc: Sumit Semwal <sumit.semwal@linaro.org>
> > > > > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > > > > ---
> > > > >   drivers/dma-buf/dma-buf.c    | 67
> > > ++++++++++++++++++++++++++++++++++++
> > > > >   include/uapi/linux/dma-buf.h | 35 +++++++++++++++++++
> > > > >   2 files changed, 102 insertions(+)
> > > > >
> > > > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > > > > index 79795857be3e..6ff54f7e6119 100644
> > > > > --- a/drivers/dma-buf/dma-buf.c
> > > > > +++ b/drivers/dma-buf/dma-buf.c
> > > > > @@ -20,6 +20,7 @@
> > > > >   #include <linux/debugfs.h>
> > > > >   #include <linux/module.h>
> > > > >   #include <linux/seq_file.h>
> > > > > +#include <linux/sync_file.h>
> > > > >   #include <linux/poll.h>
> > > > >   #include <linux/dma-resv.h>
> > > > >   #include <linux/mm.h>
> > > > > @@ -192,6 +193,9 @@ static loff_t dma_buf_llseek(struct file *file,
> > > loff_t offset, int whence)
> > > > >    * Note that this only signals the completion of the respective
> > > fences, i.e. the
> > > > >    * DMA transfers are complete. Cache flushing and any other
> necessary
> > > > >    * preparations before CPU access can begin still need to happen.
> > > > > + *
> > > > > + * As an alternative to poll(), the set of fences on DMA buffer
> can be
> > > > > + * exported as a &sync_file using &dma_buf_sync_file_export.
> > > > >    */
> > > > >   static void dma_buf_poll_cb(struct dma_fence *fence, struct
> > > dma_fence_cb *cb)
> > > > > @@ -326,6 +330,64 @@ static long dma_buf_set_name(struct dma_buf
> > > *dmabuf, const char __user *buf)
> > > > >     return 0;
> > > > >   }
> > > > > +#if IS_ENABLED(CONFIG_SYNC_FILE)
> > > > > +static long dma_buf_export_sync_file(struct dma_buf *dmabuf,
> > > > > +                                void __user *user_data)
> > > > > +{
> > > > > +   struct dma_buf_export_sync_file arg;
> > > > > +   enum dma_resv_usage usage;
> > > > > +   struct dma_fence *fence = NULL;
> > > > > +   struct sync_file *sync_file;
> > > > > +   int fd, ret;
> > > > > +
> > > > > +   if (copy_from_user(&arg, user_data, sizeof(arg)))
> > > > > +           return -EFAULT;
> > > > > +
> > > > > +   if (arg.flags & ~DMA_BUF_SYNC_RW)
> > > > > +           return -EINVAL;
> > > > > +
> > > > > +   if ((arg.flags & DMA_BUF_SYNC_RW) == 0)
> > > > > +           return -EINVAL;
> > > > > +
> > > > > +   fd = get_unused_fd_flags(O_CLOEXEC);
> > > > > +   if (fd < 0)
> > > > > +           return fd;
> > > > > +
> > > > > +   usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
> > > > > +   ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
> > > > > +   if (ret)
> > > > > +           goto err_put_fd;
> > > > > +
> > > > > +   if (!fence)
> > > > > +           fence = dma_fence_get_stub();
> > > > > +
> > > > > +   sync_file = sync_file_create(fence);
> > > > > +
> > > > > +   dma_fence_put(fence);
> > > > > +
> > > > > +   if (!sync_file) {
> > > > > +           ret = -ENOMEM;
> > > > > +           goto err_put_fd;
> > > > > +   }
> > > > > +
> > > > > +   arg.fd = fd;
> > > > > +   if (copy_to_user(user_data, &arg, sizeof(arg))) {
> > > > > +           ret = -EFAULT;
> > > > > +           goto err_put_file;
> > > > > +   }
> > > > > +
> > > > > +   fd_install(fd, sync_file->file);
> > > > > +
> > > > > +   return 0;
> > > > > +
> > > > > +err_put_file:
> > > > > +   fput(sync_file->file);
> > > > > +err_put_fd:
> > > > > +   put_unused_fd(fd);
> > > > > +   return ret;
> > > > > +}
> > > > > +#endif
> > > > > +
> > > > >   static long dma_buf_ioctl(struct file *file,
> > > > >                       unsigned int cmd, unsigned long arg)
> > > > >   {
> > > > > @@ -369,6 +431,11 @@ static long dma_buf_ioctl(struct file *file,
> > > > >     case DMA_BUF_SET_NAME_B:
> > > > >             return dma_buf_set_name(dmabuf, (const char __user
> *)arg);
> > > > > +#if IS_ENABLED(CONFIG_SYNC_FILE)
> > > > > +   case DMA_BUF_IOCTL_EXPORT_SYNC_FILE:
> > > > > +           return dma_buf_export_sync_file(dmabuf, (void __user
> > > *)arg);
> > > > > +#endif
> > > > > +
> > > > >     default:
> > > > >             return -ENOTTY;
> > > > >     }
> > > > > diff --git a/include/uapi/linux/dma-buf.h
> > > b/include/uapi/linux/dma-buf.h
> > > > > index 8e4a2ca0bcbf..46f1e3e98b02 100644
> > > > > --- a/include/uapi/linux/dma-buf.h
> > > > > +++ b/include/uapi/linux/dma-buf.h
> > > > > @@ -85,6 +85,40 @@ struct dma_buf_sync {
> > > > >   #define DMA_BUF_NAME_LEN  32
> > > > > +/**
> > > > > + * struct dma_buf_export_sync_file - Get a sync_file from a
> dma-buf
> > > > > + *
> > > > > + * Userspace can perform a DMA_BUF_IOCTL_EXPORT_SYNC_FILE to
> retrieve
> > > the
> > > > > + * current set of fences on a dma-buf file descriptor as a
> > > sync_file.  CPU
> > > > > + * waits via poll() or other driver-specific mechanisms typically
> > > wait on
> > > > > + * whatever fences are on the dma-buf at the time the wait begins.
> > > This
> > > > > + * is similar except that it takes a snapshot of the current
> fences
> > > on the
> > > > > + * dma-buf for waiting later instead of waiting immediately.
> This is
> > > > > + * useful for modern graphics APIs such as Vulkan which assume an
> > > explicit
> > > > > + * synchronization model but still need to inter-operate with
> dma-buf.
> > > > > + */
> > > > > +struct dma_buf_export_sync_file {
> > > > > +   /**
> > > > > +    * @flags: Read/write flags
> > > > > +    *
> > > > > +    * Must be DMA_BUF_SYNC_READ, DMA_BUF_SYNC_WRITE, or both.
> > > > > +    *
> > > > > +    * If DMA_BUF_SYNC_READ is set and DMA_BUF_SYNC_WRITE is not
> set,
> > > > > +    * the returned sync file waits on any writers of the dma-buf
> to
> > > > > +    * complete.  Waiting on the returned sync file is equivalent
> to
> > > > > +    * poll() with POLLIN.
> > > > > +    *
> > > > > +    * If DMA_BUF_SYNC_WRITE is set, the returned sync file waits
> on
> > > > > +    * any users of the dma-buf (read or write) to complete.
> Waiting
> > > > > +    * on the returned sync file is equivalent to poll() with
> POLLOUT.
> > > > > +    * If both DMA_BUF_SYNC_WRITE and DMA_BUF_SYNC_READ are set,
> this
> > > > > +    * is equivalent to just DMA_BUF_SYNC_WRITE.
> > > > > +    */
> > > > > +   __u32 flags;
> > > > > +   /** @fd: Returned sync file descriptor */
> > > > > +   __s32 fd;
> > > > > +};
> > > > > +
> > > > >   #define DMA_BUF_BASE              'b'
> > > > >   #define DMA_BUF_IOCTL_SYNC        _IOW(DMA_BUF_BASE, 0, struct
> > > dma_buf_sync)
> > > > > @@ -94,5 +128,6 @@ struct dma_buf_sync {
> > > > >   #define DMA_BUF_SET_NAME  _IOW(DMA_BUF_BASE, 1, const char *)
> > > > >   #define DMA_BUF_SET_NAME_A        _IOW(DMA_BUF_BASE, 1, u32)
> > > > >   #define DMA_BUF_SET_NAME_B        _IOW(DMA_BUF_BASE, 1, u64)
> > > > > +#define DMA_BUF_IOCTL_EXPORT_SYNC_FILE     _IOWR(DMA_BUF_BASE, 2,
> > > struct dma_buf_export_sync_file)
> > > > >   #endif
> > > >
> > >
> > > --
> > > Daniel Vetter
> > > Software Engineer, Intel Corporation
> > > http://blog.ffwll.ch
> > >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
>

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Re: [PATCH 2/2] dma-buf: Add an API for importing sync files (v9)

[Simon Ser]

On Friday, May 6th, 2022 at 20:02, Jason Ekstrand <jason@jlekstrand.net> wrote:

> diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h
> index 46f1e3e98b02..70e213a0d7d9 100644
> --- a/include/uapi/linux/dma-buf.h
> +++ b/include/uapi/linux/dma-buf.h
> @@ -96,6 +96,24 @@ struct dma_buf_sync {
>   * dma-buf for waiting later instead of waiting immediately.  This is
>   * useful for modern graphics APIs such as Vulkan which assume an explicit
>   * synchronization model but still need to inter-operate with dma-buf.
> + *
> + * The intended usage pattern is the following:
> + *
> + *  1. Export a sync_file with flags corresponding to the expected GPU usage
> + *     via DMA_BUF_IOCTL_EXPORT_SYNC_FILE.
> + *
> + *  2. Submit rendering work which uses the dma-buf.  The work should wait on
> + *     the exported sync file before rendering and produce another sync_file
> + *     when complete.
> + *
> + *  3. Import the rendering-complete sync_file into the dma-buf with flags
> + *     corresponding to the GPU usage via DMA_BUF_IOCTL_EXPORT_SYNC_FILE.

This should read DMA_BUF_IOCTL_IMPORT_SYNC_FILE I think?

> + * Unlike doing implicit synchronization via a GPU kernel driver's exec ioctl,
> + * the above is not a single atomic operation.  If userspace wants to ensure
> + * ordering via these fences, it is the respnosibility of userspace to use
> + * locks or other mechanisms to ensure that no other context adds fences or
> + * submits work between steps 1 and 3 above.
>   */
>  struct dma_buf_export_sync_file {
>  	/**

Re: [PATCH 0/2] dma-buf: Add an API for exporting sync files (v14)

[Bas Nieuwenhuizen]

Acked-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>

Didn't test the latest version of everything, but I can confirm the
UAPI worked fine for what we'd want to use it for with radv.

On Thu, May 26, 2022 at 8:47 AM Jason Ekstrand <jason@jlekstrand.net> wrote:
>
> On Wed, May 25, 2022 at 5:02 AM Daniel Stone <daniel@fooishbar.org> wrote:
>>
>> On Sat, 7 May 2022 at 14:18, Jason Ekstrand <jason@jlekstrand.net> wrote:
>> > This patch series actually contains two new ioctls.  There is the export one
>> > mentioned above as well as an RFC for an import ioctl which provides the other
>> > half.  The intention is to land the export ioctl since it seems like there's
>> > no real disagreement on that one.  The import ioctl, however, has a lot of
>> > debate around it so it's intended to be RFC-only for now.
>>
>> Errr, I think we're good with this one now right?
>
>
> Yeah, I dropped the RFC from the patch, just not the description in the cover letter, apparently.
>
>>
>> From the uAPI point of view, having looked through the Mesa MR, both are:
>> Acked-by: Daniel Stone <daniels@collabora.com>
>
>
> For reference: https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4037
>
> Yes, I agree it's gotten sufficient review at this point that I think we can call the uAPI reviewed.  I'm good with landing now.  Sorry that took so long but the original version I had only used half of the new API and I wanted to make sure both halves got good testing.
>
> --Jason
>
>
>>
>> Cheers,
>> Daniel

Re: [PATCH 0/2] dma-buf: Add an API for exporting sync files (v14)

[Simon Ser]

The uAPI looks good to me as well, if that helps.

Acked-by: Simon Ser <contact@emersion.fr>

Re: [PATCH 1/2] dma-buf: Add an API for exporting sync files (v14)

[kernel test robot]

Hi Jason,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on tegra-drm/drm/tegra/for-next]
[cannot apply to drm-tip/drm-tip linus/master v5.19-rc1 next-20220609]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/intel-lab-lkp/linux/commits/Jason-Ekstrand/dma-buf-Add-an-API-for-exporting-sync-files-v15/20220608-232447
base:   git://anongit.freedesktop.org/tegra/linux.git drm/tegra/for-next
config: i386-randconfig-a014 (https://download.01.org/0day-ci/archive/20220610/202206100914.FWjiKmaa-lkp@intel.com/config)
compiler: gcc-11 (Debian 11.3.0-3) 11.3.0
reproduce (this is a W=1 build):
        # https://github.com/intel-lab-lkp/linux/commit/d9d427e1ab310adae7e076f2531d00862d74a120
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Jason-Ekstrand/dma-buf-Add-an-API-for-exporting-sync-files-v15/20220608-232447
        git checkout d9d427e1ab310adae7e076f2531d00862d74a120
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash drivers/dma-buf/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   drivers/dma-buf/dma-buf.c: In function 'dma_buf_export_sync_file':
   drivers/dma-buf/dma-buf.c:337:29: error: storage size of 'usage' isn't known
     337 |         enum dma_resv_usage usage;
         |                             ^~~~~
   drivers/dma-buf/dma-buf.c:355:17: error: implicit declaration of function 'dma_resv_usage_rw' [-Werror=implicit-function-declaration]
     355 |         usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
         |                 ^~~~~~~~~~~~~~~~~
   drivers/dma-buf/dma-buf.c:356:15: error: implicit declaration of function 'dma_resv_get_singleton'; did you mean 'dma_resv_test_signaled'? [-Werror=implicit-function-declaration]
     356 |         ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
         |               ^~~~~~~~~~~~~~~~~~~~~~
         |               dma_resv_test_signaled
>> drivers/dma-buf/dma-buf.c:337:29: warning: unused variable 'usage' [-Wunused-variable]
     337 |         enum dma_resv_usage usage;
         |                             ^~~~~
   cc1: some warnings being treated as errors


vim +/usage +337 drivers/dma-buf/dma-buf.c

   331	
   332	#if IS_ENABLED(CONFIG_SYNC_FILE)
   333	static long dma_buf_export_sync_file(struct dma_buf *dmabuf,
   334					     void __user *user_data)
   335	{
   336		struct dma_buf_export_sync_file arg;
 > 337		enum dma_resv_usage usage;
   338		struct dma_fence *fence = NULL;
   339		struct sync_file *sync_file;
   340		int fd, ret;
   341	
   342		if (copy_from_user(&arg, user_data, sizeof(arg)))
   343			return -EFAULT;
   344	
   345		if (arg.flags & ~DMA_BUF_SYNC_RW)
   346			return -EINVAL;
   347	
   348		if ((arg.flags & DMA_BUF_SYNC_RW) == 0)
   349			return -EINVAL;
   350	
   351		fd = get_unused_fd_flags(O_CLOEXEC);
   352		if (fd < 0)
   353			return fd;
   354	
   355		usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
   356		ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
   357		if (ret)
   358			goto err_put_fd;
   359	
   360		if (!fence)
   361			fence = dma_fence_get_stub();
   362	
   363		sync_file = sync_file_create(fence);
   364	
   365		dma_fence_put(fence);
   366	
   367		if (!sync_file) {
   368			ret = -ENOMEM;
   369			goto err_put_fd;
   370		}
   371	
   372		arg.fd = fd;
   373		if (copy_to_user(user_data, &arg, sizeof(arg))) {
   374			ret = -EFAULT;
   375			goto err_put_file;
   376		}
   377	
   378		fd_install(fd, sync_file->file);
   379	
   380		return 0;
   381	
   382	err_put_file:
   383		fput(sync_file->file);
   384	err_put_fd:
   385		put_unused_fd(fd);
   386		return ret;
   387	}
   388	#endif
   389	

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

Re: [PATCH 1/2] dma-buf: Add an API for exporting sync files (v14)

[kernel test robot]

Hi Jason,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on tegra-drm/drm/tegra/for-next]
[cannot apply to drm-tip/drm-tip linus/master v5.19-rc1 next-20220608]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/intel-lab-lkp/linux/commits/Jason-Ekstrand/dma-buf-Add-an-API-for-exporting-sync-files-v15/20220608-232447
base:   git://anongit.freedesktop.org/tegra/linux.git drm/tegra/for-next
config: arc-randconfig-r043-20220608 (https://download.01.org/0day-ci/archive/20220609/202206090724.2BjpdEjC-lkp@intel.com/config)
compiler: arceb-elf-gcc (GCC) 11.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/d9d427e1ab310adae7e076f2531d00862d74a120
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Jason-Ekstrand/dma-buf-Add-an-API-for-exporting-sync-files-v15/20220608-232447
        git checkout d9d427e1ab310adae7e076f2531d00862d74a120
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.3.0 make.cross W=1 O=build_dir ARCH=arc SHELL=/bin/bash drivers/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   drivers/dma-buf/dma-buf.c: In function 'dma_buf_export_sync_file':
>> drivers/dma-buf/dma-buf.c:337:29: error: storage size of 'usage' isn't known
     337 |         enum dma_resv_usage usage;
         |                             ^~~~~
>> drivers/dma-buf/dma-buf.c:355:17: error: implicit declaration of function 'dma_resv_usage_rw' [-Werror=implicit-function-declaration]
     355 |         usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
         |                 ^~~~~~~~~~~~~~~~~
>> drivers/dma-buf/dma-buf.c:356:15: error: implicit declaration of function 'dma_resv_get_singleton'; did you mean 'dma_resv_test_signaled'? [-Werror=implicit-function-declaration]
     356 |         ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
         |               ^~~~~~~~~~~~~~~~~~~~~~
         |               dma_resv_test_signaled
   drivers/dma-buf/dma-buf.c:337:29: warning: unused variable 'usage' [-Wunused-variable]
     337 |         enum dma_resv_usage usage;
         |                             ^~~~~
   cc1: some warnings being treated as errors


vim +337 drivers/dma-buf/dma-buf.c

   331	
   332	#if IS_ENABLED(CONFIG_SYNC_FILE)
   333	static long dma_buf_export_sync_file(struct dma_buf *dmabuf,
   334					     void __user *user_data)
   335	{
   336		struct dma_buf_export_sync_file arg;
 > 337		enum dma_resv_usage usage;
   338		struct dma_fence *fence = NULL;
   339		struct sync_file *sync_file;
   340		int fd, ret;
   341	
   342		if (copy_from_user(&arg, user_data, sizeof(arg)))
   343			return -EFAULT;
   344	
   345		if (arg.flags & ~DMA_BUF_SYNC_RW)
   346			return -EINVAL;
   347	
   348		if ((arg.flags & DMA_BUF_SYNC_RW) == 0)
   349			return -EINVAL;
   350	
   351		fd = get_unused_fd_flags(O_CLOEXEC);
   352		if (fd < 0)
   353			return fd;
   354	
 > 355		usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
 > 356		ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
   357		if (ret)
   358			goto err_put_fd;
   359	
   360		if (!fence)
   361			fence = dma_fence_get_stub();
   362	
   363		sync_file = sync_file_create(fence);
   364	
   365		dma_fence_put(fence);
   366	
   367		if (!sync_file) {
   368			ret = -ENOMEM;
   369			goto err_put_fd;
   370		}
   371	
   372		arg.fd = fd;
   373		if (copy_to_user(user_data, &arg, sizeof(arg))) {
   374			ret = -EFAULT;
   375			goto err_put_file;
   376		}
   377	
   378		fd_install(fd, sync_file->file);
   379	
   380		return 0;
   381	
   382	err_put_file:
   383		fput(sync_file->file);
   384	err_put_fd:
   385		put_unused_fd(fd);
   386		return ret;
   387	}
   388	#endif
   389	

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

Re: [PATCH 1/2] dma-buf: Add an API for exporting sync files (v14)

Hi Jason,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on tegra-drm/drm/tegra/for-next]
[cannot apply to drm-tip/drm-tip linus/master v5.19-rc1 next-20220608]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/intel-lab-lkp/linux/commits/Jason-Ekstrand/dma-buf-Add-an-API-for-exporting-sync-files-v15/20220608-232447
base:   git://anongit.freedesktop.org/tegra/linux.git drm/tegra/for-next
config: hexagon-randconfig-r041-20220608 (https://download.01.org/0day-ci/archive/20220609/202206090608.jRFcxzQE-lkp@intel.com/config)
compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project b92436efcb7813fc481b30f2593a4907568d917a)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/d9d427e1ab310adae7e076f2531d00862d74a120
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Jason-Ekstrand/dma-buf-Add-an-API-for-exporting-sync-files-v15/20220608-232447
        git checkout d9d427e1ab310adae7e076f2531d00862d74a120
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=hexagon SHELL=/bin/bash drivers/dma-buf/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> drivers/dma-buf/dma-buf.c:337:22: error: variable has incomplete type 'enum dma_resv_usage'
           enum dma_resv_usage usage;
                               ^
   drivers/dma-buf/dma-buf.c:337:7: note: forward declaration of 'enum dma_resv_usage'
           enum dma_resv_usage usage;
                ^
>> drivers/dma-buf/dma-buf.c:355:10: error: implicit declaration of function 'dma_resv_usage_rw' [-Werror,-Wimplicit-function-declaration]
           usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
                   ^
>> drivers/dma-buf/dma-buf.c:356:8: error: implicit declaration of function 'dma_resv_get_singleton' [-Werror,-Wimplicit-function-declaration]
           ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
                 ^
   3 errors generated.


vim +337 drivers/dma-buf/dma-buf.c

   331	
   332	#if IS_ENABLED(CONFIG_SYNC_FILE)
   333	static long dma_buf_export_sync_file(struct dma_buf *dmabuf,
   334					     void __user *user_data)
   335	{
   336		struct dma_buf_export_sync_file arg;
 > 337		enum dma_resv_usage usage;
   338		struct dma_fence *fence = NULL;
   339		struct sync_file *sync_file;
   340		int fd, ret;
   341	
   342		if (copy_from_user(&arg, user_data, sizeof(arg)))
   343			return -EFAULT;
   344	
   345		if (arg.flags & ~DMA_BUF_SYNC_RW)
   346			return -EINVAL;
   347	
   348		if ((arg.flags & DMA_BUF_SYNC_RW) == 0)
   349			return -EINVAL;
   350	
   351		fd = get_unused_fd_flags(O_CLOEXEC);
   352		if (fd < 0)
   353			return fd;
   354	
 > 355		usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
 > 356		ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
   357		if (ret)
   358			goto err_put_fd;
   359	
   360		if (!fence)
   361			fence = dma_fence_get_stub();
   362	
   363		sync_file = sync_file_create(fence);
   364	
   365		dma_fence_put(fence);
   366	
   367		if (!sync_file) {
   368			ret = -ENOMEM;
   369			goto err_put_fd;
   370		}
   371	
   372		arg.fd = fd;
   373		if (copy_to_user(user_data, &arg, sizeof(arg))) {
   374			ret = -EFAULT;
   375			goto err_put_file;
   376		}
   377	
   378		fd_install(fd, sync_file->file);
   379	
   380		return 0;
   381	
   382	err_put_file:
   383		fput(sync_file->file);
   384	err_put_fd:
   385		put_unused_fd(fd);
   386		return ret;
   387	}
   388	#endif
   389	

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

Re: [PATCH 1/2] dma-buf: Add an API for exporting sync files (v14)

[kernel test robot]

Hi Jason,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on tegra-drm/drm/tegra/for-next]
[cannot apply to drm-tip/drm-tip linus/master v5.19-rc1 next-20220608]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/intel-lab-lkp/linux/commits/Jason-Ekstrand/dma-buf-Add-an-API-for-exporting-sync-files-v15/20220608-232447
base:   git://anongit.freedesktop.org/tegra/linux.git drm/tegra/for-next
config: hexagon-randconfig-r041-20220608 (https://download.01.org/0day-ci/archive/20220609/202206090608.jRFcxzQE-lkp@intel.com/config)
compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project b92436efcb7813fc481b30f2593a4907568d917a)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/d9d427e1ab310adae7e076f2531d00862d74a120
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Jason-Ekstrand/dma-buf-Add-an-API-for-exporting-sync-files-v15/20220608-232447
        git checkout d9d427e1ab310adae7e076f2531d00862d74a120
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=hexagon SHELL=/bin/bash drivers/dma-buf/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> drivers/dma-buf/dma-buf.c:337:22: error: variable has incomplete type 'enum dma_resv_usage'
           enum dma_resv_usage usage;
                               ^
   drivers/dma-buf/dma-buf.c:337:7: note: forward declaration of 'enum dma_resv_usage'
           enum dma_resv_usage usage;
                ^
>> drivers/dma-buf/dma-buf.c:355:10: error: implicit declaration of function 'dma_resv_usage_rw' [-Werror,-Wimplicit-function-declaration]
           usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
                   ^
>> drivers/dma-buf/dma-buf.c:356:8: error: implicit declaration of function 'dma_resv_get_singleton' [-Werror,-Wimplicit-function-declaration]
           ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
                 ^
   3 errors generated.


vim +337 drivers/dma-buf/dma-buf.c

   331	
   332	#if IS_ENABLED(CONFIG_SYNC_FILE)
   333	static long dma_buf_export_sync_file(struct dma_buf *dmabuf,
   334					     void __user *user_data)
   335	{
   336		struct dma_buf_export_sync_file arg;
 > 337		enum dma_resv_usage usage;
   338		struct dma_fence *fence = NULL;
   339		struct sync_file *sync_file;
   340		int fd, ret;
   341	
   342		if (copy_from_user(&arg, user_data, sizeof(arg)))
   343			return -EFAULT;
   344	
   345		if (arg.flags & ~DMA_BUF_SYNC_RW)
   346			return -EINVAL;
   347	
   348		if ((arg.flags & DMA_BUF_SYNC_RW) == 0)
   349			return -EINVAL;
   350	
   351		fd = get_unused_fd_flags(O_CLOEXEC);
   352		if (fd < 0)
   353			return fd;
   354	
 > 355		usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
 > 356		ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
   357		if (ret)
   358			goto err_put_fd;
   359	
   360		if (!fence)
   361			fence = dma_fence_get_stub();
   362	
   363		sync_file = sync_file_create(fence);
   364	
   365		dma_fence_put(fence);
   366	
   367		if (!sync_file) {
   368			ret = -ENOMEM;
   369			goto err_put_fd;
   370		}
   371	
   372		arg.fd = fd;
   373		if (copy_to_user(user_data, &arg, sizeof(arg))) {
   374			ret = -EFAULT;
   375			goto err_put_file;
   376		}
   377	
   378		fd_install(fd, sync_file->file);
   379	
   380		return 0;
   381	
   382	err_put_file:
   383		fput(sync_file->file);
   384	err_put_fd:
   385		put_unused_fd(fd);
   386		return ret;
   387	}
   388	#endif
   389	

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

Re: [PATCH 1/2] dma-buf: Add an API for exporting sync files (v14)

[Simon Ser]

Both patches pushed to drm-misc-next, thanks for your contribution!

[PATCH 1/2] dma-buf: Add an API for exporting sync files (v14)

[Jason Ekstrand]

Modern userspace APIs like Vulkan are built on an explicit
synchronization model.  This doesn't always play nicely with the
implicit synchronization used in the kernel and assumed by X11 and
Wayland.  The client -> compositor half of the synchronization isn't too
bad, at least on intel, because we can control whether or not i915
synchronizes on the buffer and whether or not it's considered written.

The harder part is the compositor -> client synchronization when we get
the buffer back from the compositor.  We're required to be able to
provide the client with a VkSemaphore and VkFence representing the point
in time where the window system (compositor and/or display) finished
using the buffer.  With current APIs, it's very hard to do this in such
a way that we don't get confused by the Vulkan driver's access of the
buffer.  In particular, once we tell the kernel that we're rendering to
the buffer again, any CPU waits on the buffer or GPU dependencies will
wait on some of the client rendering and not just the compositor.

This new IOCTL solves this problem by allowing us to get a snapshot of
the implicit synchronization state of a given dma-buf in the form of a
sync file.  It's effectively the same as a poll() or I915_GEM_WAIT only,
instead of CPU waiting directly, it encapsulates the wait operation, at
the current moment in time, in a sync_file so we can check/wait on it
later.  As long as the Vulkan driver does the sync_file export from the
dma-buf before we re-introduce it for rendering, it will only contain
fences from the compositor or display.  This allows to accurately turn
it into a VkFence or VkSemaphore without any over-synchronization.

By making this an ioctl on the dma-buf itself, it allows this new
functionality to be used in an entirely driver-agnostic way without
having access to a DRM fd. This makes it ideal for use in driver-generic
code in Mesa or in a client such as a compositor where the DRM fd may be
hard to reach.

v2 (Jason Ekstrand):
 - Use a wrapper dma_fence_array of all fences including the new one
   when importing an exclusive fence.

v3 (Jason Ekstrand):
 - Lock around setting shared fences as well as exclusive
 - Mark SIGNAL_SYNC_FILE as a read-write ioctl.
 - Initialize ret to 0 in dma_buf_wait_sync_file

v4 (Jason Ekstrand):
 - Use the new dma_resv_get_singleton helper

v5 (Jason Ekstrand):
 - Rename the IOCTLs to import/export rather than wait/signal
 - Drop the WRITE flag and always get/set the exclusive fence

v6 (Jason Ekstrand):
 - Drop the sync_file import as it was all-around sketchy and not nearly
   as useful as import.
 - Re-introduce READ/WRITE flag support for export
 - Rework the commit message

v7 (Jason Ekstrand):
 - Require at least one sync flag
 - Fix a refcounting bug: dma_resv_get_excl() doesn't take a reference
 - Use _rcu helpers since we're accessing the dma_resv read-only

v8 (Jason Ekstrand):
 - Return -ENOMEM if the sync_file_create fails
 - Predicate support on IS_ENABLED(CONFIG_SYNC_FILE)

v9 (Jason Ekstrand):
 - Add documentation for the new ioctl

v10 (Jason Ekstrand):
 - Go back to dma_buf_sync_file as the ioctl struct name

v11 (Daniel Vetter):
 - Go back to dma_buf_export_sync_file as the ioctl struct name
 - Better kerneldoc describing what the read/write flags do

v12 (Christian König):
 - Document why we chose to make it an ioctl on dma-buf

v13 (Jason Ekstrand):
 - Rebase on Christian König's fence rework

v14 (Daniel Vetter & Christian König):
 - Use dma_rev_usage_rw to get the properly inverted usage to pass to
   dma_resv_get_singleton()
 - Clean up the sync_file and fd if copy_to_user() fails

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Signed-off-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Acked-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
---
 drivers/dma-buf/dma-buf.c    | 67 ++++++++++++++++++++++++++++++++++++
 include/uapi/linux/dma-buf.h | 35 +++++++++++++++++++
 2 files changed, 102 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 79795857be3e..6ff54f7e6119 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -20,6 +20,7 @@
 #include <linux/debugfs.h>
 #include <linux/module.h>
 #include <linux/seq_file.h>
+#include <linux/sync_file.h>
 #include <linux/poll.h>
 #include <linux/dma-resv.h>
 #include <linux/mm.h>
@@ -192,6 +193,9 @@ static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
  * Note that this only signals the completion of the respective fences, i.e. the
  * DMA transfers are complete. Cache flushing and any other necessary
  * preparations before CPU access can begin still need to happen.
+ *
+ * As an alternative to poll(), the set of fences on DMA buffer can be
+ * exported as a &sync_file using &dma_buf_sync_file_export.
  */
 
 static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
@@ -326,6 +330,64 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
 	return 0;
 }
 
+#if IS_ENABLED(CONFIG_SYNC_FILE)
+static long dma_buf_export_sync_file(struct dma_buf *dmabuf,
+				     void __user *user_data)
+{
+	struct dma_buf_export_sync_file arg;
+	enum dma_resv_usage usage;
+	struct dma_fence *fence = NULL;
+	struct sync_file *sync_file;
+	int fd, ret;
+
+	if (copy_from_user(&arg, user_data, sizeof(arg)))
+		return -EFAULT;
+
+	if (arg.flags & ~DMA_BUF_SYNC_RW)
+		return -EINVAL;
+
+	if ((arg.flags & DMA_BUF_SYNC_RW) == 0)
+		return -EINVAL;
+
+	fd = get_unused_fd_flags(O_CLOEXEC);
+	if (fd < 0)
+		return fd;
+
+	usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE);
+	ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence);
+	if (ret)
+		goto err_put_fd;
+
+	if (!fence)
+		fence = dma_fence_get_stub();
+
+	sync_file = sync_file_create(fence);
+
+	dma_fence_put(fence);
+
+	if (!sync_file) {
+		ret = -ENOMEM;
+		goto err_put_fd;
+	}
+
+	arg.fd = fd;
+	if (copy_to_user(user_data, &arg, sizeof(arg))) {
+		ret = -EFAULT;
+		goto err_put_file;
+	}
+
+	fd_install(fd, sync_file->file);
+
+	return 0;
+
+err_put_file:
+	fput(sync_file->file);
+err_put_fd:
+	put_unused_fd(fd);
+	return ret;
+}
+#endif
+
 static long dma_buf_ioctl(struct file *file,
 			  unsigned int cmd, unsigned long arg)
 {
@@ -369,6 +431,11 @@ static long dma_buf_ioctl(struct file *file,
 	case DMA_BUF_SET_NAME_B:
 		return dma_buf_set_name(dmabuf, (const char __user *)arg);
 
+#if IS_ENABLED(CONFIG_SYNC_FILE)
+	case DMA_BUF_IOCTL_EXPORT_SYNC_FILE:
+		return dma_buf_export_sync_file(dmabuf, (void __user *)arg);
+#endif
+
 	default:
 		return -ENOTTY;
 	}
diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h
index 8e4a2ca0bcbf..46f1e3e98b02 100644
--- a/include/uapi/linux/dma-buf.h
+++ b/include/uapi/linux/dma-buf.h
@@ -85,6 +85,40 @@ struct dma_buf_sync {
 
 #define DMA_BUF_NAME_LEN	32
 
+/**
+ * struct dma_buf_export_sync_file - Get a sync_file from a dma-buf
+ *
+ * Userspace can perform a DMA_BUF_IOCTL_EXPORT_SYNC_FILE to retrieve the
+ * current set of fences on a dma-buf file descriptor as a sync_file.  CPU
+ * waits via poll() or other driver-specific mechanisms typically wait on
+ * whatever fences are on the dma-buf at the time the wait begins.  This
+ * is similar except that it takes a snapshot of the current fences on the
+ * dma-buf for waiting later instead of waiting immediately.  This is
+ * useful for modern graphics APIs such as Vulkan which assume an explicit
+ * synchronization model but still need to inter-operate with dma-buf.
+ */
+struct dma_buf_export_sync_file {
+	/**
+	 * @flags: Read/write flags
+	 *
+	 * Must be DMA_BUF_SYNC_READ, DMA_BUF_SYNC_WRITE, or both.
+	 *
+	 * If DMA_BUF_SYNC_READ is set and DMA_BUF_SYNC_WRITE is not set,
+	 * the returned sync file waits on any writers of the dma-buf to
+	 * complete.  Waiting on the returned sync file is equivalent to
+	 * poll() with POLLIN.
+	 *
+	 * If DMA_BUF_SYNC_WRITE is set, the returned sync file waits on
+	 * any users of the dma-buf (read or write) to complete.  Waiting
+	 * on the returned sync file is equivalent to poll() with POLLOUT.
+	 * If both DMA_BUF_SYNC_WRITE and DMA_BUF_SYNC_READ are set, this
+	 * is equivalent to just DMA_BUF_SYNC_WRITE.
+	 */
+	__u32 flags;
+	/** @fd: Returned sync file descriptor */
+	__s32 fd;
+};
+
 #define DMA_BUF_BASE		'b'
 #define DMA_BUF_IOCTL_SYNC	_IOW(DMA_BUF_BASE, 0, struct dma_buf_sync)
 
@@ -94,5 +128,6 @@ struct dma_buf_sync {
 #define DMA_BUF_SET_NAME	_IOW(DMA_BUF_BASE, 1, const char *)
 #define DMA_BUF_SET_NAME_A	_IOW(DMA_BUF_BASE, 1, u32)
 #define DMA_BUF_SET_NAME_B	_IOW(DMA_BUF_BASE, 1, u64)
+#define DMA_BUF_IOCTL_EXPORT_SYNC_FILE	_IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file)
 
 #endif
-- 
2.36.1