[PATCH v5 0/6] small vhost changes and in-band notifications

[PATCH v5 0/6] small vhost changes and in-band notifications

[Johannes Berg]

Hi,

Here's a repost of all the patches I sent back in August, with the
in-band notifications rebased over the reset patch, so IDs have now
changed a bit.

I've marked this all as v5 even if it really wasn't for all of them,
just the VugDev main fd cleanup patch was at v4 before.

I've also collected reviewed-by's from the previous patches here.

Let me know if I should make any further edits here or in follow-up
patches.

Thanks,
johannes

[PATCH v5 1/6] libvhost-user: implement VHOST_USER_PROTOCOL_F_REPLY_ACK

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

This is really simple, since we know whether a response is
already requested or not, so we can just send a (successful)
response when there isn't one already.

Given that, it's not all _that_ useful but the master can at
least be sure the message was processed, and we can exercise
more code paths using the example code.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 contrib/libvhost-user/libvhost-user.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
index ec27b78ff108..8cc3054fd510 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -1168,7 +1168,8 @@ vu_get_protocol_features_exec(VuDev *dev, VhostUserMsg *vmsg)
                         1ULL << VHOST_USER_PROTOCOL_F_LOG_SHMFD |
                         1ULL << VHOST_USER_PROTOCOL_F_SLAVE_REQ |
                         1ULL << VHOST_USER_PROTOCOL_F_HOST_NOTIFIER |
-                        1ULL << VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD;
+                        1ULL << VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD |
+                        1ULL << VHOST_USER_PROTOCOL_F_REPLY_ACK;
 
     if (have_userfault()) {
         features |= 1ULL << VHOST_USER_PROTOCOL_F_PAGEFAULT;
@@ -1550,13 +1551,20 @@ vu_dispatch(VuDev *dev)
 {
     VhostUserMsg vmsg = { 0, };
     int reply_requested;
-    bool success = false;
+    bool need_reply, success = false;
 
     if (!vu_message_read(dev, dev->sock, &vmsg)) {
         goto end;
     }
 
+    need_reply = vmsg.flags & VHOST_USER_NEED_REPLY_MASK;
+
     reply_requested = vu_process_message(dev, &vmsg);
+    if (!reply_requested && need_reply) {
+        vmsg_set_reply_u64(&vmsg, 0);
+        reply_requested = 1;
+    }
+
     if (!reply_requested) {
         success = true;
         goto end;
-- 
2.24.1

[PATCH v5 2/6] libvhost-user-glib: fix VugDev main fd cleanup

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

If you try to make a device implementation that can handle multiple
connections and allow disconnections (which requires overriding the
VHOST_USER_NONE handling), then glib will warn that we remove a src
while it's still on the mainloop, and will poll() an FD that doesn't
exist anymore.

Fix this by making vug_source_new() require pairing with the new
vug_source_destroy() so we can keep the GSource referenced in the
meantime.

Note that this requires calling the new API in vhost-user-input.
vhost-user-gpu also uses vug_source_new(), but never seems to free
the result at all, so I haven't changed anything there.

Fixes: 8bb7ddb78a1c ("libvhost-user: add glib source helper")
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 contrib/libvhost-user/libvhost-user-glib.c | 15 ++++++++++++---
 contrib/libvhost-user/libvhost-user-glib.h |  1 +
 contrib/vhost-user-input/main.c            |  6 ++----
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/contrib/libvhost-user/libvhost-user-glib.c b/contrib/libvhost-user/libvhost-user-glib.c
index 99edd2f3de45..824c7780de61 100644
--- a/contrib/libvhost-user/libvhost-user-glib.c
+++ b/contrib/libvhost-user/libvhost-user-glib.c
@@ -91,7 +91,6 @@ vug_source_new(VugDev *gdev, int fd, GIOCondition cond,
     g_source_add_poll(gsrc, &src->gfd);
     id = g_source_attach(gsrc, NULL);
     g_assert(id);
-    g_source_unref(gsrc);
 
     return gsrc;
 }
@@ -131,6 +130,16 @@ static void vug_watch(VuDev *dev, int condition, void *data)
     }
 }
 
+void vug_source_destroy(GSource *src)
+{
+    if (!src) {
+        return;
+    }
+
+    g_source_destroy(src);
+    g_source_unref(src);
+}
+
 bool
 vug_init(VugDev *dev, uint16_t max_queues, int socket,
          vu_panic_cb panic, const VuDevIface *iface)
@@ -144,7 +153,7 @@ vug_init(VugDev *dev, uint16_t max_queues, int socket,
     }
 
     dev->fdmap = g_hash_table_new_full(NULL, NULL, NULL,
-                                       (GDestroyNotify) g_source_destroy);
+                                       (GDestroyNotify) vug_source_destroy);
 
     dev->src = vug_source_new(dev, socket, G_IO_IN, vug_watch, NULL);
 
@@ -157,5 +166,5 @@ vug_deinit(VugDev *dev)
     g_assert(dev);
 
     g_hash_table_unref(dev->fdmap);
-    g_source_unref(dev->src);
+    vug_source_destroy(dev->src);
 }
diff --git a/contrib/libvhost-user/libvhost-user-glib.h b/contrib/libvhost-user/libvhost-user-glib.h
index 64d539d93aba..1a79a4916ef2 100644
--- a/contrib/libvhost-user/libvhost-user-glib.h
+++ b/contrib/libvhost-user/libvhost-user-glib.h
@@ -31,5 +31,6 @@ void vug_deinit(VugDev *dev);
 
 GSource *vug_source_new(VugDev *dev, int fd, GIOCondition cond,
                         vu_watch_cb vu_cb, gpointer data);
+void vug_source_destroy(GSource *src);
 
 #endif /* LIBVHOST_USER_GLIB_H */
diff --git a/contrib/vhost-user-input/main.c b/contrib/vhost-user-input/main.c
index ef4b7769f285..6020c6f33a46 100644
--- a/contrib/vhost-user-input/main.c
+++ b/contrib/vhost-user-input/main.c
@@ -187,7 +187,7 @@ vi_queue_set_started(VuDev *dev, int qidx, bool started)
     }
 
     if (!started && vi->evsrc) {
-        g_source_destroy(vi->evsrc);
+        vug_source_destroy(vi->evsrc);
         vi->evsrc = NULL;
     }
 }
@@ -401,9 +401,7 @@ main(int argc, char *argv[])
 
     vug_deinit(&vi.dev);
 
-    if (vi.evsrc) {
-        g_source_unref(vi.evsrc);
-    }
+    vug_source_destroy(vi.evsrc);
     g_array_free(vi.config, TRUE);
     g_free(vi.queue);
     return 0;
-- 
2.24.1

[PATCH v5 3/6] libvhost-user-glib: use g_main_context_get_thread_default()

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

If we use NULL, we just get the main program default mainloop
here. Using g_main_context_get_thread_default() has basically
the same effect, but it lets us start different devices in
different threads with different mainloops, which can be useful.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 contrib/libvhost-user/libvhost-user-glib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/contrib/libvhost-user/libvhost-user-glib.c b/contrib/libvhost-user/libvhost-user-glib.c
index 824c7780de61..53f1ca4cdd73 100644
--- a/contrib/libvhost-user/libvhost-user-glib.c
+++ b/contrib/libvhost-user/libvhost-user-glib.c
@@ -89,7 +89,7 @@ vug_source_new(VugDev *gdev, int fd, GIOCondition cond,
     src->gfd.events = cond;
 
     g_source_add_poll(gsrc, &src->gfd);
-    id = g_source_attach(gsrc, NULL);
+    id = g_source_attach(gsrc, g_main_context_get_thread_default());
     g_assert(id);
 
     return gsrc;
-- 
2.24.1

[PATCH v5 4/6] libvhost-user: handle NOFD flag in call/kick/err better

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

The code here is odd, for example will it print out invalid
file descriptor numbers that were never sent in the message.

Clean that up a bit so it's actually possible to implement
a device that uses polling.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 contrib/libvhost-user/libvhost-user.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
index 8cc3054fd510..34d08e2fc4be 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -920,6 +920,7 @@ static bool
 vu_check_queue_msg_file(VuDev *dev, VhostUserMsg *vmsg)
 {
     int index = vmsg->payload.u64 & VHOST_USER_VRING_IDX_MASK;
+    bool nofd = vmsg->payload.u64 & VHOST_USER_VRING_NOFD_MASK;
 
     if (index >= dev->max_queues) {
         vmsg_close_fds(vmsg);
@@ -927,8 +928,12 @@ vu_check_queue_msg_file(VuDev *dev, VhostUserMsg *vmsg)
         return false;
     }
 
-    if (vmsg->payload.u64 & VHOST_USER_VRING_NOFD_MASK ||
-        vmsg->fd_num != 1) {
+    if (nofd) {
+        vmsg_close_fds(vmsg);
+        return true;
+    }
+
+    if (vmsg->fd_num != 1) {
         vmsg_close_fds(vmsg);
         vu_panic(dev, "Invalid fds in request: %d", vmsg->request);
         return false;
@@ -1025,6 +1030,7 @@ static bool
 vu_set_vring_kick_exec(VuDev *dev, VhostUserMsg *vmsg)
 {
     int index = vmsg->payload.u64 & VHOST_USER_VRING_IDX_MASK;
+    bool nofd = vmsg->payload.u64 & VHOST_USER_VRING_NOFD_MASK;
 
     DPRINT("u64: 0x%016"PRIx64"\n", vmsg->payload.u64);
 
@@ -1038,8 +1044,8 @@ vu_set_vring_kick_exec(VuDev *dev, VhostUserMsg *vmsg)
         dev->vq[index].kick_fd = -1;
     }
 
-    dev->vq[index].kick_fd = vmsg->fds[0];
-    DPRINT("Got kick_fd: %d for vq: %d\n", vmsg->fds[0], index);
+    dev->vq[index].kick_fd = nofd ? -1 : vmsg->fds[0];
+    DPRINT("Got kick_fd: %d for vq: %d\n", dev->vq[index].kick_fd, index);
 
     dev->vq[index].started = true;
     if (dev->iface->queue_set_started) {
@@ -1116,6 +1122,7 @@ static bool
 vu_set_vring_call_exec(VuDev *dev, VhostUserMsg *vmsg)
 {
     int index = vmsg->payload.u64 & VHOST_USER_VRING_IDX_MASK;
+    bool nofd = vmsg->payload.u64 & VHOST_USER_VRING_NOFD_MASK;
 
     DPRINT("u64: 0x%016"PRIx64"\n", vmsg->payload.u64);
 
@@ -1128,14 +1135,14 @@ vu_set_vring_call_exec(VuDev *dev, VhostUserMsg *vmsg)
         dev->vq[index].call_fd = -1;
     }
 
-    dev->vq[index].call_fd = vmsg->fds[0];
+    dev->vq[index].call_fd = nofd ? -1 : vmsg->fds[0];
 
     /* in case of I/O hang after reconnecting */
-    if (eventfd_write(vmsg->fds[0], 1)) {
+    if (dev->vq[index].call_fd != -1 && eventfd_write(vmsg->fds[0], 1)) {
         return -1;
     }
 
-    DPRINT("Got call_fd: %d for vq: %d\n", vmsg->fds[0], index);
+    DPRINT("Got call_fd: %d for vq: %d\n", dev->vq[index].call_fd, index);
 
     return false;
 }
@@ -1144,6 +1151,7 @@ static bool
 vu_set_vring_err_exec(VuDev *dev, VhostUserMsg *vmsg)
 {
     int index = vmsg->payload.u64 & VHOST_USER_VRING_IDX_MASK;
+    bool nofd = vmsg->payload.u64 & VHOST_USER_VRING_NOFD_MASK;
 
     DPRINT("u64: 0x%016"PRIx64"\n", vmsg->payload.u64);
 
@@ -1156,7 +1164,7 @@ vu_set_vring_err_exec(VuDev *dev, VhostUserMsg *vmsg)
         dev->vq[index].err_fd = -1;
     }
 
-    dev->vq[index].err_fd = vmsg->fds[0];
+    dev->vq[index].err_fd = nofd ? -1 : vmsg->fds[0];
 
     return false;
 }
-- 
2.24.1

[PATCH v5 5/6] docs: vhost-user: add in-band kick/call messages

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

For good reason, vhost-user is currently built asynchronously, that
way better performance can be obtained. However, for certain use
cases such as simulation, this is problematic.

Consider an event-based simulation in which both the device and CPU
have scheduled according to a simulation "calendar". Now, consider
the CPU sending I/O to the device, over a vring in the vhost-user
protocol. In this case, the CPU must wait for the vring interrupt
to have been processed by the device, so that the device is able to
put an entry onto the simulation calendar to obtain time to handle
the interrupt. Note that this doesn't mean the I/O is actually done
at this time, it just means that the handling of it is scheduled
before the CPU can continue running.

This cannot be done with the asynchronous eventfd based vring kick
and call design.

Extend the protocol slightly, so that a message can be used for kick
and call instead, if VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS is
negotiated. This in itself doesn't guarantee synchronisation, but both
sides can also negotiate VHOST_USER_PROTOCOL_F_REPLY_ACK and thus get
a reply to this message by setting the need_reply flag, and ensure
synchronisation this way.

To really use it in both directions, VHOST_USER_PROTOCOL_F_SLAVE_REQ
is also needed.

Since it is used for simulation purposes and too many messages on
the socket can lock up the virtual machine, document that this should
only be used together with the mentioned features.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 docs/interop/vhost-user.rst | 122 ++++++++++++++++++++++++++++++------
 1 file changed, 104 insertions(+), 18 deletions(-)

diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
index 5f8b3a456b5e..401652397cac 100644
--- a/docs/interop/vhost-user.rst
+++ b/docs/interop/vhost-user.rst
@@ -2,6 +2,7 @@
 Vhost-user Protocol
 ===================
 :Copyright: 2014 Virtual Open Systems Sarl.
+:Copyright: 2019 Intel Corporation
 :Licence: This work is licensed under the terms of the GNU GPL,
           version 2 or later. See the COPYING file in the top-level
           directory.
@@ -279,6 +280,9 @@ If *master* is unable to send the full message or receives a wrong
 reply it will close the connection. An optional reconnection mechanism
 can be implemented.
 
+If *slave* detects some error such as incompatible features, it may also
+close the connection. This should only happen in exceptional circumstances.
+
 Any protocol extensions are gated by protocol feature bits, which
 allows full backwards compatibility on both master and slave.  As
 older slaves don't support negotiating protocol features, a feature
@@ -315,7 +319,8 @@ it until ring is started, or after it has been stopped.
 
 Client must start ring upon receiving a kick (that is, detecting that
 file descriptor is readable) on the descriptor specified by
-``VHOST_USER_SET_VRING_KICK``, and stop ring upon receiving
+``VHOST_USER_SET_VRING_KICK`` or receiving the in-band message
+``VHOST_USER_VRING_KICK`` if negotiated, and stop ring upon receiving
 ``VHOST_USER_GET_VRING_BASE``.
 
 While processing the rings (whether they are enabled or not), client
@@ -767,25 +772,49 @@ When reconnecting:
 #. Resubmit inflight ``DescStatePacked`` entries in order of their
    counter value
 
+In-band notifications
+---------------------
+
+In some limited situations (e.g. for simulation) it is desirable to
+have the kick, call and error (if used) signals done via in-band
+messages instead of asynchronous eventfd notifications. This can be
+done by negotiating the ``VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS``
+protocol feature.
+
+Note that due to the fact that too many messages on the sockets can
+cause the sending application(s) to block, it is not advised to use
+this feature unless absolutely necessary. It is also considered an
+error to negotiate this feature without also negotiating
+``VHOST_USER_PROTOCOL_F_SLAVE_REQ`` and ``VHOST_USER_PROTOCOL_F_REPLY_ACK``,
+the former is necessary for getting a message channel from the slave
+to the master, while the latter needs to be used with the in-band
+notification messages to block until they are processed, both to avoid
+blocking later and for proper processing (at least in the simulation
+use case.) As it has no other way of signalling this error, the slave
+should close the connection as a response to a
+``VHOST_USER_SET_PROTOCOL_FEATURES`` message that sets the in-band
+notifications feature flag without the other two.
+
 Protocol features
 -----------------
 
 .. code:: c
 
-  #define VHOST_USER_PROTOCOL_F_MQ             0
-  #define VHOST_USER_PROTOCOL_F_LOG_SHMFD      1
-  #define VHOST_USER_PROTOCOL_F_RARP           2
-  #define VHOST_USER_PROTOCOL_F_REPLY_ACK      3
-  #define VHOST_USER_PROTOCOL_F_MTU            4
-  #define VHOST_USER_PROTOCOL_F_SLAVE_REQ      5
-  #define VHOST_USER_PROTOCOL_F_CROSS_ENDIAN   6
-  #define VHOST_USER_PROTOCOL_F_CRYPTO_SESSION 7
-  #define VHOST_USER_PROTOCOL_F_PAGEFAULT      8
-  #define VHOST_USER_PROTOCOL_F_CONFIG         9
-  #define VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD  10
-  #define VHOST_USER_PROTOCOL_F_HOST_NOTIFIER  11
-  #define VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD 12
-  #define VHOST_USER_PROTOCOL_F_RESET_DEVICE   13
+  #define VHOST_USER_PROTOCOL_F_MQ                    0
+  #define VHOST_USER_PROTOCOL_F_LOG_SHMFD             1
+  #define VHOST_USER_PROTOCOL_F_RARP                  2
+  #define VHOST_USER_PROTOCOL_F_REPLY_ACK             3
+  #define VHOST_USER_PROTOCOL_F_MTU                   4
+  #define VHOST_USER_PROTOCOL_F_SLAVE_REQ             5
+  #define VHOST_USER_PROTOCOL_F_CROSS_ENDIAN          6
+  #define VHOST_USER_PROTOCOL_F_CRYPTO_SESSION        7
+  #define VHOST_USER_PROTOCOL_F_PAGEFAULT             8
+  #define VHOST_USER_PROTOCOL_F_CONFIG                9
+  #define VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD        10
+  #define VHOST_USER_PROTOCOL_F_HOST_NOTIFIER        11
+  #define VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD       12
+  #define VHOST_USER_PROTOCOL_F_RESET_DEVICE         13
+  #define VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS 14
 
 Master message types
 --------------------
@@ -947,7 +976,12 @@ Master message types
   Bits (0-7) of the payload contain the vring index. Bit 8 is the
   invalid FD flag. This flag is set when there is no file descriptor
   in the ancillary data. This signals that polling should be used
-  instead of waiting for a kick.
+  instead of waiting for the kick. Note that if the protocol feature
+  ``VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS`` has been negotiated
+  this message isn't necessary as the ring is also started on the
+  ``VHOST_USER_VRING_KICK`` message, it may however still be used to
+  set an event file descriptor (which will be preferred over the
+  message) or to enable polling.
 
 ``VHOST_USER_SET_VRING_CALL``
   :id: 13
@@ -960,7 +994,12 @@ Master message types
   Bits (0-7) of the payload contain the vring index. Bit 8 is the
   invalid FD flag. This flag is set when there is no file descriptor
   in the ancillary data. This signals that polling will be used
-  instead of waiting for the call.
+  instead of waiting for the call. Note that if the protocol features
+  ``VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS`` and
+  ``VHOST_USER_PROTOCOL_F_SLAVE_REQ`` have been negotiated this message
+  isn't necessary as the ``VHOST_USER_SLAVE_VRING_CALL`` message can be
+  used, it may however still be used to set an event file descriptor
+  or to enable polling.
 
 ``VHOST_USER_SET_VRING_ERR``
   :id: 14
@@ -972,7 +1011,12 @@ Master message types
 
   Bits (0-7) of the payload contain the vring index. Bit 8 is the
   invalid FD flag. This flag is set when there is no file descriptor
-  in the ancillary data.
+  in the ancillary data. Note that if the protocol features
+  ``VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS`` and
+  ``VHOST_USER_PROTOCOL_F_SLAVE_REQ`` have been negotiated this message
+  isn't necessary as the ``VHOST_USER_SLAVE_VRING_ERR`` message can be
+  used, it may however still be used to set an event file descriptor
+  (which will be preferred over the message).
 
 ``VHOST_USER_GET_QUEUE_NUM``
   :id: 17
@@ -1205,6 +1249,20 @@ Master message types
   Only valid if the ``VHOST_USER_PROTOCOL_F_RESET_DEVICE`` protocol
   feature is set by the backend.
 
+``VHOST_USER_VRING_KICK``
+  :id: 35
+  :equivalent ioctl: N/A
+  :slave payload: vring state description
+  :master payload: N/A
+
+  When the ``VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS`` protocol
+  feature has been successfully negotiated, this message may be
+  submitted by the master to indicate that a buffer was added to
+  the vring instead of signalling it using the vring's kick file
+  descriptor or having the slave rely on polling.
+
+  The state.num field is currently reserved and must be set to 0.
+
 Slave message types
 -------------------
 
@@ -1261,6 +1319,34 @@ Slave message types
   ``VHOST_USER_PROTOCOL_F_HOST_NOTIFIER`` protocol feature has been
   successfully negotiated.
 
+``VHOST_USER_SLAVE_VRING_CALL``
+  :id: 4
+  :equivalent ioctl: N/A
+  :slave payload: vring state description
+  :master payload: N/A
+
+  When the ``VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS`` protocol
+  feature has been successfully negotiated, this message may be
+  submitted by the slave to indicate that a buffer was used from
+  the vring instead of signalling this using the vring's call file
+  descriptor or having the master relying on polling.
+
+  The state.num field is currently reserved and must be set to 0.
+
+``VHOST_USER_SLAVE_VRING_ERR``
+  :id: 5
+  :equivalent ioctl: N/A
+  :slave payload: vring state description
+  :master payload: N/A
+
+  When the ``VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS`` protocol
+  feature has been successfully negotiated, this message may be
+  submitted by the slave to indicate that an error occurred on the
+  specific vring, instead of signalling the error file descriptor
+  set by the master via ``VHOST_USER_SET_VRING_ERR``.
+
+  The state.num field is currently reserved and must be set to 0.
+
 .. _reply_ack:
 
 VHOST_USER_PROTOCOL_F_REPLY_ACK
-- 
2.24.1

[PATCH v5 6/6] libvhost-user: implement in-band notifications

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

Add support for VHOST_USER_PROTOCOL_F_IN_BAND_NOTIFICATIONS, but
as it's not desired by default, don't enable it unless the device
implementation opts in by returning it from its protocol features
callback.

Note that I updated vu_set_vring_err_exec(), but didn't add any
sending of the VHOST_USER_SLAVE_VRING_ERR message as there's no
write to the err_fd today either.

This also adds vu_queue_notify_sync() which can be used to force
a synchronous notification if inband notifications are supported.
Previously, I had left out the slave->master direction handling
of F_REPLY_ACK, this now adds some code to support it as well.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 contrib/libvhost-user/libvhost-user.c | 103 +++++++++++++++++++++++++-
 contrib/libvhost-user/libvhost-user.h |  14 ++++
 2 files changed, 114 insertions(+), 3 deletions(-)

diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
index 34d08e2fc4be..5cb8e6e32158 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -136,6 +136,7 @@ vu_request_to_string(unsigned int req)
         REQ(VHOST_USER_GET_INFLIGHT_FD),
         REQ(VHOST_USER_SET_INFLIGHT_FD),
         REQ(VHOST_USER_GPU_SET_SOCKET),
+        REQ(VHOST_USER_VRING_KICK),
         REQ(VHOST_USER_MAX),
     };
 #undef REQ
@@ -163,7 +164,10 @@ vu_panic(VuDev *dev, const char *msg, ...)
     dev->panic(dev, buf);
     free(buf);
 
-    /* FIXME: find a way to call virtio_error? */
+    /*
+     * FIXME:
+     * find a way to call virtio_error, or perhaps close the connection?
+     */
 }
 
 /* Translate guest physical address to our virtual address.  */
@@ -1172,6 +1176,14 @@ vu_set_vring_err_exec(VuDev *dev, VhostUserMsg *vmsg)
 static bool
 vu_get_protocol_features_exec(VuDev *dev, VhostUserMsg *vmsg)
 {
+    /*
+     * Note that we support, but intentionally do not set,
+     * VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS. This means that
+     * a device implementation can return it in its callback
+     * (get_protocol_features) if it wants to use this for
+     * simulation, but it is otherwise not desirable (if even
+     * implemented by the master.)
+     */
     uint64_t features = 1ULL << VHOST_USER_PROTOCOL_F_MQ |
                         1ULL << VHOST_USER_PROTOCOL_F_LOG_SHMFD |
                         1ULL << VHOST_USER_PROTOCOL_F_SLAVE_REQ |
@@ -1204,6 +1216,25 @@ vu_set_protocol_features_exec(VuDev *dev, VhostUserMsg *vmsg)
 
     dev->protocol_features = vmsg->payload.u64;
 
+    if (vu_has_protocol_feature(dev,
+                                VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS) &&
+        (!vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_SLAVE_REQ) ||
+         !vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_REPLY_ACK))) {
+        /*
+         * The use case for using messages for kick/call is simulation, to make
+         * the kick and call synchronous. To actually get that behaviour, both
+         * of the other features are required.
+         * Theoretically, one could use only kick messages, or do them without
+         * having F_REPLY_ACK, but too many (possibly pending) messages on the
+         * socket will eventually cause the master to hang, to avoid this in
+         * scenarios where not desired enforce that the settings are in a way
+         * that actually enables the simulation case.
+         */
+        vu_panic(dev,
+                 "F_IN_BAND_NOTIFICATIONS requires F_SLAVE_REQ && F_REPLY_ACK");
+        return false;
+    }
+
     if (dev->iface->set_protocol_features) {
         dev->iface->set_protocol_features(dev, features);
     }
@@ -1464,6 +1495,34 @@ vu_set_inflight_fd(VuDev *dev, VhostUserMsg *vmsg)
     return false;
 }
 
+static bool
+vu_handle_vring_kick(VuDev *dev, VhostUserMsg *vmsg)
+{
+    unsigned int index = vmsg->payload.state.index;
+
+    if (index >= dev->max_queues) {
+        vu_panic(dev, "Invalid queue index: %u", index);
+        return false;
+    }
+
+    DPRINT("Got kick message: handler:%p idx:%d\n",
+           dev->vq[index].handler, index);
+
+    if (!dev->vq[index].started) {
+        dev->vq[index].started = true;
+
+        if (dev->iface->queue_set_started) {
+            dev->iface->queue_set_started(dev, index, true);
+        }
+    }
+
+    if (dev->vq[index].handler) {
+        dev->vq[index].handler(dev, index);
+    }
+
+    return false;
+}
+
 static bool
 vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
 {
@@ -1546,6 +1605,8 @@ vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
         return vu_get_inflight_fd(dev, vmsg);
     case VHOST_USER_SET_INFLIGHT_FD:
         return vu_set_inflight_fd(dev, vmsg);
+    case VHOST_USER_VRING_KICK:
+        return vu_handle_vring_kick(dev, vmsg);
     default:
         vmsg_close_fds(vmsg);
         vu_panic(dev, "Unhandled request: %d", vmsg->request);
@@ -2005,8 +2066,7 @@ vring_notify(VuDev *dev, VuVirtq *vq)
     return !v || vring_need_event(vring_get_used_event(vq), new, old);
 }
 
-void
-vu_queue_notify(VuDev *dev, VuVirtq *vq)
+static void _vu_queue_notify(VuDev *dev, VuVirtq *vq, bool sync)
 {
     if (unlikely(dev->broken) ||
         unlikely(!vq->vring.avail)) {
@@ -2018,11 +2078,48 @@ vu_queue_notify(VuDev *dev, VuVirtq *vq)
         return;
     }
 
+    if (vq->call_fd < 0 &&
+        vu_has_protocol_feature(dev,
+                                VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS) &&
+        vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_SLAVE_REQ)) {
+        VhostUserMsg vmsg = {
+            .request = VHOST_USER_SLAVE_VRING_CALL,
+            .flags = VHOST_USER_VERSION,
+            .size = sizeof(vmsg.payload.state),
+            .payload.state = {
+                .index = vq - dev->vq,
+            },
+        };
+        bool ack = sync &&
+                   vu_has_protocol_feature(dev,
+                                           VHOST_USER_PROTOCOL_F_REPLY_ACK);
+
+        if (ack) {
+            vmsg.flags |= VHOST_USER_NEED_REPLY_MASK;
+        }
+
+        vu_message_write(dev, dev->slave_fd, &vmsg);
+        if (ack) {
+            vu_message_read(dev, dev->slave_fd, &vmsg);
+        }
+        return;
+    }
+
     if (eventfd_write(vq->call_fd, 1) < 0) {
         vu_panic(dev, "Error writing eventfd: %s", strerror(errno));
     }
 }
 
+void vu_queue_notify(VuDev *dev, VuVirtq *vq)
+{
+    _vu_queue_notify(dev, vq, false);
+}
+
+void vu_queue_notify_sync(VuDev *dev, VuVirtq *vq)
+{
+    _vu_queue_notify(dev, vq, true);
+}
+
 static inline void
 vring_used_flags_set_bit(VuVirtq *vq, int mask)
 {
diff --git a/contrib/libvhost-user/libvhost-user.h b/contrib/libvhost-user/libvhost-user.h
index 46b600799b2e..cd12cbd92cc5 100644
--- a/contrib/libvhost-user/libvhost-user.h
+++ b/contrib/libvhost-user/libvhost-user.h
@@ -53,6 +53,7 @@ enum VhostUserProtocolFeature {
     VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD = 10,
     VHOST_USER_PROTOCOL_F_HOST_NOTIFIER = 11,
     VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD = 12,
+    VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS = 14,
 
     VHOST_USER_PROTOCOL_F_MAX
 };
@@ -94,6 +95,7 @@ typedef enum VhostUserRequest {
     VHOST_USER_GET_INFLIGHT_FD = 31,
     VHOST_USER_SET_INFLIGHT_FD = 32,
     VHOST_USER_GPU_SET_SOCKET = 33,
+    VHOST_USER_VRING_KICK = 35,
     VHOST_USER_MAX
 } VhostUserRequest;
 
@@ -102,6 +104,8 @@ typedef enum VhostUserSlaveRequest {
     VHOST_USER_SLAVE_IOTLB_MSG = 1,
     VHOST_USER_SLAVE_CONFIG_CHANGE_MSG = 2,
     VHOST_USER_SLAVE_VRING_HOST_NOTIFIER_MSG = 3,
+    VHOST_USER_SLAVE_VRING_CALL = 4,
+    VHOST_USER_SLAVE_VRING_ERR = 5,
     VHOST_USER_SLAVE_MAX
 }  VhostUserSlaveRequest;
 
@@ -522,6 +526,16 @@ bool vu_queue_empty(VuDev *dev, VuVirtq *vq);
  */
 void vu_queue_notify(VuDev *dev, VuVirtq *vq);
 
+/**
+ * vu_queue_notify_sync:
+ * @dev: a VuDev context
+ * @vq: a VuVirtq queue
+ *
+ * Request to notify the queue via callfd (skipped if unnecessary)
+ * or sync message if possible.
+ */
+void vu_queue_notify_sync(VuDev *dev, VuVirtq *vq);
+
 /**
  * vu_queue_pop:
  * @dev: a VuDev context
-- 
2.24.1

Re: [PATCH v5 0/6] small vhost changes and in-band notifications

[Johannes Berg]

On Thu, 2020-01-23 at 09:17 +0100, Johannes Berg wrote:
> Hi,
> 
> Here's a repost of all the patches I sent back in August, with the
> in-band notifications rebased over the reset patch, so IDs have now
> changed a bit.

Ping?

The patches still apply on top of latest qemu.

I wanted to send some corresponding kernel patches, but without the
protocol nailed down ...

johannes

Re: [PATCH v5 0/6] small vhost changes and in-band notifications

[Michael S. Tsirkin]

On Thu, Feb 13, 2020 at 02:26:10PM +0100, Johannes Berg wrote:
> On Thu, 2020-01-23 at 09:17 +0100, Johannes Berg wrote:
> > Hi,
> > 
> > Here's a repost of all the patches I sent back in August, with the
> > in-band notifications rebased over the reset patch, so IDs have now
> > changed a bit.
> 
> Ping?
> 
> The patches still apply on top of latest qemu.
> 
> I wanted to send some corresponding kernel patches, but without the
> protocol nailed down ...
> 
> johannes

Queued, thanks!