Re: [PULL 04/14] vhost-user: fix shared object lookup handler logic

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Nov 10, 2025 at 04:57:51PM +0100, Albert Esteve wrote:
> On Mon, Nov 10, 2025 at 4:42 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Mon, Nov 10, 2025 at 10:23:25AM +0100, Albert Esteve wrote:
> > > On Sun, Nov 9, 2025 at 3:35 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> > > >
> > > > From: Albert Esteve <aesteve@redhat.com>
> > > >
> > > > Refactor backend_read() function and add a reply_ack variable
> > > > to have the option for handlers to force tweak whether they should
> > > > send a reply or not without depending on VHOST_USER_NEED_REPLY_MASK
> > > > flag.
> > > >
> > > > This fixes an issue with
> > > > vhost_user_backend_handle_shared_object_lookup() logic, as the
> > > > error path was not closing the backend channel correctly. So,
> > > > we can remove the reply call from within the handler, make
> > > > sure it returns early on errors as other handlers do and
> > > > set the reply_ack variable on backend_read() to true to ensure
> > > > that it will send a response, thus keeping the original intent.
> > >
> > > Hey Michal,
> > >
> > > This patch was
> > > Based-on: <20251016143827.1850397-1-aesteve@redhat.com>
> > > … for main.
> >
> > That's the SHMEM thing right?  Yes but I rebased it dropping
> > the SHMEM dependency.
> >
> > At least, I think I did it correctly.
> 
> Yes, removing the dependency is correctly applied. But that was only
> required for the backport to stable.
> 
> If we merge this patch to main without the one it is based on, then
> I'd need to send a new version of the SHMEM patch with the block that
> you have dropped. I can do it, but I was trying to prioritize the
> other one, as it was a lot harder to get approved. That is why I based
> this patch on top of the SHMEM one and not the other way around.
> 
> Sorry if that was not clear from the message.


Right but I can't apply SHMEM patch in freeze so yes, it has to go
on top. Sorry it's like this.

> >
> > > As this was the first time I did this based-on thingy, I am just
> > > making sure that the other patch was not missed.
> > > If this PULL is only targeting stable, then it's ok as is.
> >
> > It is targeting 10.2 which is in freeze. So equivalently same.
> >
> >
> > > BR,
> > > Albert
> > >
> > > >
> > > > Fixes: 1609476662 ("vhost-user: add shared_object msg")
> > > > Cc: qemu-stable@nongnu.org
> > > > Signed-off-by: Albert Esteve <aesteve@redhat.com>
> > > > Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
> > > > Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> > > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > > Message-Id: <20251017072011.1874874-2-aesteve@redhat.com>
> > > > ---
> > > >  hw/virtio/vhost-user.c | 40 +++++++++++++---------------------------
> > > >  1 file changed, 13 insertions(+), 27 deletions(-)
> > > >
> > > > diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> > > > index aac98f898a..4b0fae12ae 100644
> > > > --- a/hw/virtio/vhost-user.c
> > > > +++ b/hw/virtio/vhost-user.c
> > > > @@ -1668,14 +1668,6 @@ static bool vhost_user_send_resp(QIOChannel *ioc, VhostUserHeader *hdr,
> > > >      return !qio_channel_writev_all(ioc, iov, ARRAY_SIZE(iov), errp);
> > > >  }
> > > >
> > > > -static bool
> > > > -vhost_user_backend_send_dmabuf_fd(QIOChannel *ioc, VhostUserHeader *hdr,
> > > > -                                  VhostUserPayload *payload, Error **errp)
> > > > -{
> > > > -    hdr->size = sizeof(payload->u64);
> > > > -    return vhost_user_send_resp(ioc, hdr, payload, errp);
> > > > -}
> > > > -
> > > >  int vhost_user_get_shared_object(struct vhost_dev *dev, unsigned char *uuid,
> > > >                                   int *dmabuf_fd)
> > > >  {
> > > > @@ -1716,19 +1708,15 @@ int vhost_user_get_shared_object(struct vhost_dev *dev, unsigned char *uuid,
> > > >
> > > >  static int
> > > >  vhost_user_backend_handle_shared_object_lookup(struct vhost_user *u,
> > > > -                                               QIOChannel *ioc,
> > > > -                                               VhostUserHeader *hdr,
> > > > -                                               VhostUserPayload *payload)
> > > > +                                               VhostUserShared *object)
> > > >  {
> > > >      QemuUUID uuid;
> > > >      CharFrontend *chr = u->user->chr;
> > > > -    Error *local_err = NULL;
> > > >      int dmabuf_fd = -1;
> > > >      int fd_num = 0;
> > > >
> > > > -    memcpy(uuid.data, payload->object.uuid, sizeof(payload->object.uuid));
> > > > +    memcpy(uuid.data, object->uuid, sizeof(object->uuid));
> > > >
> > > > -    payload->u64 = 0;
> > > >      switch (virtio_object_type(&uuid)) {
> > > >      case TYPE_DMABUF:
> > > >          dmabuf_fd = virtio_lookup_dmabuf(&uuid);
> > > > @@ -1737,18 +1725,16 @@ vhost_user_backend_handle_shared_object_lookup(struct vhost_user *u,
> > > >      {
> > > >          struct vhost_dev *dev = virtio_lookup_vhost_device(&uuid);
> > > >          if (dev == NULL) {
> > > > -            payload->u64 = -EINVAL;
> > > > -            break;
> > > > +            return -EINVAL;
> > > >          }
> > > >          int ret = vhost_user_get_shared_object(dev, uuid.data, &dmabuf_fd);
> > > >          if (ret < 0) {
> > > > -            payload->u64 = ret;
> > > > +            return ret;
> > > >          }
> > > >          break;
> > > >      }
> > > >      case TYPE_INVALID:
> > > > -        payload->u64 = -EINVAL;
> > > > -        break;
> > > > +        return -EINVAL;
> > > >      }
> > > >
> > > >      if (dmabuf_fd != -1) {
> > > > @@ -1757,11 +1743,6 @@ vhost_user_backend_handle_shared_object_lookup(struct vhost_user *u,
> > > >
> > > >      if (qemu_chr_fe_set_msgfds(chr, &dmabuf_fd, fd_num) < 0) {
> > > >          error_report("Failed to set msg fds.");
> > > > -        payload->u64 = -EINVAL;
> > > > -    }
> > > > -
> > > > -    if (!vhost_user_backend_send_dmabuf_fd(ioc, hdr, payload, &local_err)) {
> > > > -        error_report_err(local_err);
> > > >          return -EINVAL;
> > > >      }
> > > >
> > > > @@ -1790,6 +1771,7 @@ static gboolean backend_read(QIOChannel *ioc, GIOCondition condition,
> > > >      struct iovec iov;
> > > >      g_autofree int *fd = NULL;
> > > >      size_t fdsize = 0;
> > > > +    bool reply_ack;
> > > >      int i;
> > > >
> > > >      /* Read header */
> > > > @@ -1808,6 +1790,8 @@ static gboolean backend_read(QIOChannel *ioc, GIOCondition condition,
> > > >          goto err;
> > > >      }
> > > >
> > > > +    reply_ack = hdr.flags & VHOST_USER_NEED_REPLY_MASK;
> > > > +
> > > >      /* Read payload */
> > > >      if (qio_channel_read_all(ioc, (char *) &payload, hdr.size, &local_err)) {
> > > >          error_report_err(local_err);
> > > > @@ -1833,8 +1817,10 @@ static gboolean backend_read(QIOChannel *ioc, GIOCondition condition,
> > > >                                                               &payload.object);
> > > >          break;
> > > >      case VHOST_USER_BACKEND_SHARED_OBJECT_LOOKUP:
> > > > -        ret = vhost_user_backend_handle_shared_object_lookup(dev->opaque, ioc,
> > > > -                                                             &hdr, &payload);
> > > > +        /* The backend always expects a response */
> > > > +        reply_ack = true;
> > > > +        ret = vhost_user_backend_handle_shared_object_lookup(dev->opaque,
> > > > +                                                             &payload.object);
> > > >          break;
> > > >      default:
> > > >          error_report("Received unexpected msg type: %d.", hdr.request);
> > > > @@ -1845,7 +1831,7 @@ static gboolean backend_read(QIOChannel *ioc, GIOCondition condition,
> > > >       * REPLY_ACK feature handling. Other reply types has to be managed
> > > >       * directly in their request handlers.
> > > >       */
> > > > -    if (hdr.flags & VHOST_USER_NEED_REPLY_MASK) {
> > > > +    if (reply_ack) {
> > > >          payload.u64 = !!ret;
> > > >          hdr.size = sizeof(payload.u64);
> > > >
> > > > --
> > > > MST
> > > >
> >