[PATCH v5 4/5] staging/android: refactor SYNC_IOC_FILE_INFO

[Gustavo Padovan <gustavo@padovan.org>]

From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

Change SYNC_IOC_FILE_INFO behaviour to avoid future API breaks and
optimize buffer

Now num_fences can be filled by the caller to inform how many fences it
wants to retrieve from the kernel. If the num_fences passed is greater
than zero info->sync_fence_info should point to a buffer with enough space
to fit all fences.

However if num_fences passed to the kernel is 0, the kernel will reply
with number of fences of the sync_file.

Sending first an ioctl with num_fences = 0 can optimize buffer allocation,
in a first call with num_fences = 0 userspace will receive the actual
number of fences in the num_fences filed.

Then it can allocate a buffer with the correct size on sync_fence_info and
call SYNC_IOC_FILE_INFO again, but now with the actual value of num_fences
in the sync_file.

Also, info->sync_fence_info was converted to __u64 pointer to prevent
32bit compatibility issues.

An example userspace code for the later would be:

	struct sync_file_info *info;
	int err, size, num_fences;

	info = malloc(sizeof(*info));

	info.flags = 0;
	err = ioctl(fd, SYNC_IOC_FILE_INFO, info);
	num_fences = info->num_fences;

	if (num_fences) {
		info.flags = 0;
		size = sizeof(struct sync_fence_info) * num_fences;
		info->num_fences = num_fences;
		info->sync_fence_info = (uint64_t) calloc(num_fences,
							  sizeof(struct sync_fence_info));

		err = ioctl(fd, SYNC_IOC_FILE_INFO, info);
	}

v2: fix fence_info memory leak

v3: Comments from Emil Velikov
	- improve commit message
	- remove __u64 cast
	- remove check for output fields in file_info
	- clean up sync_fill_fence_info()

    Comments from Maarten Lankhorst
	- remove in.num_fences && !in.sync_fence_info check
	- remove info->len and use only num_fences to calculate size

    Comments from Dan Carpenter
	- fix info->sync_fence_info documentation

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
---
 drivers/staging/android/sync.c      | 64 ++++++++++++++++++++-----------------
 drivers/staging/android/uapi/sync.h |  9 ++----
 2 files changed, 38 insertions(+), 35 deletions(-)

diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
index dc5f382..3604e453 100644
--- a/drivers/staging/android/sync.c
+++ b/drivers/staging/android/sync.c
@@ -479,13 +479,9 @@ err_put_fd:
 	return err;
 }
 
-static int sync_fill_fence_info(struct fence *fence, void *data, int size)
+static void sync_fill_fence_info(struct fence *fence,
+				struct sync_fence_info *info)
 {
-	struct sync_fence_info *info = data;
-
-	if (size < sizeof(*info))
-		return -ENOMEM;
-
 	strlcpy(info->obj_name, fence->ops->get_timeline_name(fence),
 		sizeof(info->obj_name));
 	strlcpy(info->driver_name, fence->ops->get_driver_name(fence),
@@ -495,28 +491,20 @@ static int sync_fill_fence_info(struct fence *fence, void *data, int size)
 	else
 		info->status = 0;
 	info->timestamp_ns = ktime_to_ns(fence->timestamp);
-
-	return sizeof(*info);
 }
 
 static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 					unsigned long arg)
 {
-	struct sync_file_info *info;
+	struct sync_file_info in, *info;
+	struct sync_fence_info *fence_info = NULL;
 	__u32 size;
-	__u32 len = 0;
 	int ret, i;
 
-	if (copy_from_user(&size, (void __user *)arg, sizeof(size)))
+	if (copy_from_user(&in, (void __user *)arg, sizeof(in)))
 		return -EFAULT;
 
-	if (size < sizeof(struct sync_file_info))
-		return -EINVAL;
-
-	if (size > 4096)
-		size = 4096;
-
-	info = kzalloc(size, GFP_KERNEL);
+	info = kzalloc(sizeof(*info), GFP_KERNEL);
 	if (!info)
 		return -ENOMEM;
 
@@ -525,29 +513,47 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 	if (info->status >= 0)
 		info->status = !info->status;
 
-	info->num_fences = sync_file->num_fences;
-
-	len = sizeof(struct sync_file_info);
+	/*
+	 * Passing num_fences = 0 means that userspace doesn't want to
+	 * retrieve any sync_fence_info. If num_fences = 0 we skip filling
+	 * sync_fence_info and return the actual number of fences on
+	 * info->num_fences.
+	 */
+	if (!in.num_fences)
+		goto no_fences;
 
-	for (i = 0; i < sync_file->num_fences; ++i) {
-		struct fence *fence = sync_file->cbs[i].fence;
+	if (in.num_fences < sync_file->num_fences) {
+		ret = -EINVAL;
+		goto out;
+	}
 
-		ret = sync_fill_fence_info(fence, (u8 *)info + len, size - len);
+	size = sync_file->num_fences * sizeof(*fence_info);
+	fence_info = kzalloc(size, GFP_KERNEL);
+	if (!fence_info) {
+		ret = -ENOMEM;
+		goto out;
+	}
 
-		if (ret < 0)
-			goto out;
+	for (i = 0; i < sync_file->num_fences; ++i)
+		sync_fill_fence_info(sync_file->cbs[i].fence, &fence_info[i]);
 
-		len += ret;
+	if (copy_to_user((void __user *)in.sync_fence_info, fence_info, size)) {
+		ret = -EFAULT;
+		goto out;
 	}
 
-	info->len = len;
+	info->sync_fence_info = in.sync_fence_info;
+
+no_fences:
+	info->num_fences = sync_file->num_fences;
 
-	if (copy_to_user((void __user *)arg, info, len))
+	if (copy_to_user((void __user *)arg, info, sizeof(*info)))
 		ret = -EFAULT;
 	else
 		ret = 0;
 
 out:
+	kfree(fence_info);
 	kfree(info);
 
 	return ret;
diff --git a/drivers/staging/android/uapi/sync.h b/drivers/staging/android/uapi/sync.h
index f0b41ce..a122bb5 100644
--- a/drivers/staging/android/uapi/sync.h
+++ b/drivers/staging/android/uapi/sync.h
@@ -42,21 +42,18 @@ struct sync_fence_info {
 
 /**
  * struct sync_file_info - data returned from fence info ioctl
- * @len:	ioctl caller writes the size of the buffer its passing in.
- *		ioctl returns length of sync_file_info returned to
- *		userspace including pt_info.
  * @name:	name of fence
  * @status:	status of fence. 1: signaled 0:active <0:error
  * @num_fences	number of fences in the sync_file
- * @sync_fence_info: array of sync_fence_info for every fence in the sync_file
+ * @sync_fence_info: pointer to array of structs sync_fence_info with all
+ *		 fences in the sync_file
  */
 struct sync_file_info {
-	__u32	len;
 	char	name[32];
 	__s32	status;
 	__u32	num_fences;
 
-	__u8	sync_fence_info[0];
+	__u64	sync_fence_info;
 };
 
 #define SYNC_IOC_MAGIC		'>'
-- 
2.5.0