On Thu, 14 Mar 2019 at 19:43, Daniel P. Berrangé <berra...@redhat.com> wrote:
>
> On Thu, Mar 14, 2019 at 07:34:03AM -0400, Michael S. Tsirkin wrote:
> > On Thu, Mar 14, 2019 at 11:24:22AM +0000, Daniel P. Berrangé wrote:
> > > On Tue, Mar 12, 2019 at 12:49:35PM -0400, Michael S. Tsirkin wrote:
> > > > On Thu, Feb 28, 2019 at 04:53:54PM +0800, elohi...@gmail.com wrote:
> > > > > From: Xie Yongji <xieyon...@baidu.com>
> > > > >
> > > > > Since we now support the message VHOST_USER_GET_INFLIGHT_FD
> > > > > and VHOST_USER_SET_INFLIGHT_FD. The backend is able to restart
> > > > > safely because it can track inflight I/O in shared memory.
> > > > > This patch allows qemu to reconnect the backend after
> > > > > connection closed.
> > > > >
> > > > > Signed-off-by: Xie Yongji <xieyon...@baidu.com>
> > > > > Signed-off-by: Ni Xun <ni...@baidu.com>
> > > > > Signed-off-by: Zhang Yu <zhangy...@baidu.com>
> > > > > ---
> > > > > hw/block/vhost-user-blk.c | 205
> > > > > +++++++++++++++++++++++------
> > > > > include/hw/virtio/vhost-user-blk.h | 4 +
> > > > > 2 files changed, 167 insertions(+), 42 deletions(-)
> > >
> > >
> > > > > static void vhost_user_blk_device_realize(DeviceState *dev, Error
> > > > > **errp)
> > > > > {
> > > > > VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> > > > > VHostUserBlk *s = VHOST_USER_BLK(vdev);
> > > > > VhostUserState *user;
> > > > > - struct vhost_virtqueue *vqs = NULL;
> > > > > int i, ret;
> > > > > + Error *err = NULL;
> > > > >
> > > > > if (!s->chardev.chr) {
> > > > > error_setg(errp, "vhost-user-blk: chardev is mandatory");
> > > > > @@ -312,27 +442,28 @@ static void
> > > > > vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
> > > > > }
> > > > >
> > > > > s->inflight = g_new0(struct vhost_inflight, 1);
> > > > > -
> > > > > - s->dev.nvqs = s->num_queues;
> > > > > - s->dev.vqs = g_new(struct vhost_virtqueue, s->dev.nvqs);
> > > > > - s->dev.vq_index = 0;
> > > > > - s->dev.backend_features = 0;
> > > > > - vqs = s->dev.vqs;
> > > > > -
> > > > > - vhost_dev_set_config_notifier(&s->dev, &blk_ops);
> > > > > -
> > > > > - ret = vhost_dev_init(&s->dev, s->vhost_user,
> > > > > VHOST_BACKEND_TYPE_USER, 0);
> > > > > - if (ret < 0) {
> > > > > - error_setg(errp, "vhost-user-blk: vhost initialization
> > > > > failed: %s",
> > > > > - strerror(-ret));
> > > > > - goto virtio_err;
> > > > > - }
> > > > > + s->vqs = g_new(struct vhost_virtqueue, s->num_queues);
> > > > > + s->watch = 0;
> > > > > + s->should_start = false;
> > > > > + s->connected = false;
> > > > > +
> > > > > + qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL,
> > > > > vhost_user_blk_event,
> > > > > + NULL, (void *)dev, NULL, true);
> > > > > +
> > > > > +reconnect:
> > > > > + do {
> > > > > + if (qemu_chr_fe_wait_connected(&s->chardev, &err) < 0) {
> > > > > + error_report_err(err);
> > > > > + err = NULL;
> > > > > + sleep(1);
> > > >
> > > > Seems arbitrary. Is this basically waiting until backend will reconnect?
> > > > Why not block until event on the fd triggers?
> > > >
> > > > Also, it looks like this will just block forever with no monitor input
> > > > and no way for user to figure out what is going on short of
> > > > crashing QEMU.
> > >
> > > FWIW, the current vhost-user-net device does exactly the same thing
> > > with calling qemu_chr_fe_wait_connected during its realize() function.
> >
> > Hmm yes. It doesn't sleep for an arbitrary 1 sec so less of an eyesore :)
>
> The sleep(1) in this patch simply needs to be removed. I think that
> probably dates from when it was written against the earlier broken
> version of qemu_chr_fe_wait_connected(). That would not correctly
> deal with the "reconnect" flag, and so needing this loop with a sleep
> in it.
>
> In fact the while loop can be removed as well in this code. It just
> needs to call qemu_chr_fe_wait_connected() once. It is guaranteed
> to have a connected peer once that returns 0.
>
> qemu_chr_fe_wait_connected() only returns -1 if the operating in
> client mode, and it failed to connect and reconnect is *not*
> requested. In such case the caller should honour the failure and
> quit, not loop to retry.
>
Thanks for your comments. Will do that in next patchset.
>
> The reason vhost-user-net does a loop is because once it has a
> connection it tries todo a protocol handshake, and if that
> handshake fails it closes the chardev and tries to connect
> again. That's not the case in this blk code os the loop is
> not needed.
>
Seems like vhost-user-blk device needs to do that too.
Thanks,
Yongji
