Re: [Virtio-fs] [PATCH 4/4] virtiofsd: Implement blocking posix locks

[Vivek Goyal]

On Fri, Nov 22, 2019 at 05:47:32PM +0000, Dr. David Alan Gilbert wrote:

[..]
> > +static int virtio_send_notify_msg(struct fuse_session *se, struct iovec 
> > *iov,
> > +                             int count)
> > +{
> > +    struct fv_QueueInfo *qi;
> > +    VuDev *dev = &se->virtio_dev->dev;
> > +    VuVirtq *q;
> > +    FVRequest *req;
> > +    VuVirtqElement *elem;
> > +    unsigned int in_num, bad_in_num = 0, bad_out_num = 0;
> > +    struct fuse_out_header *out = iov[0].iov_base;
> > +    size_t in_len, tosend_len = iov_size(iov, count);
> > +    struct iovec *in_sg;
> > +    int ret = 0;
> > +
> > +    /* Notifications have unique == 0 */
> > +    assert (!out->unique);
> > +
> > +    if (!se->notify_enabled)
> > +        return -EOPNOTSUPP;
> > +
> > +    /* If notifications are enabled, queue index 1 is notification queue */
> > +    qi = se->virtio_dev->qi[1];
> > +    q = vu_get_queue(dev, qi->qidx);
> > +
> > +    pthread_rwlock_rdlock(&qi->virtio_dev->vu_dispatch_rwlock);
> > +    pthread_mutex_lock(&qi->vq_lock);
> > +    /* Pop an element from queue */
> > +    req = vu_queue_pop(dev, q, sizeof(FVRequest), &bad_in_num, 
> > &bad_out_num);
> 
> You don't need bad_in_num/bad_out_num - just pass NULL for both; they're
> only needed if you expect to read/write data that's not mappable (i.e.
> in our direct write case).

Will do.

[..]
> > @@ -1950,21 +1948,54 @@ static void lo_setlk(fuse_req_t req, fuse_ino_t ino,
> >  
> >     if (!plock) {
> >             saverr = ret;
> > +           pthread_mutex_unlock(&inode->plock_mutex);
> >             goto out;
> >     }
> >  
> > +   /*
> > +    * plock is now released when inode is going away. We already have
> > +    * a reference on inode, so it is guaranteed that plock->fd is
> > +    * still around even after dropping inode->plock_mutex lock
> > +    */
> > +   ofd = plock->fd;
> > +   pthread_mutex_unlock(&inode->plock_mutex);
> > +
> > +   /*
> > +    * If this lock request can block, request caller to wait for
> > +    * notification. Do not access req after this. Once lock is
> > +    * available, send a notification instead.
> > +    */
> > +   if (sleep && lock->l_type != F_UNLCK) {
> > +           /*
> > +            * If notification queue is not enabled, can't support async
> > +            * locks.
> > +            */
> > +           if (!se->notify_enabled) {
> > +                   saverr = EOPNOTSUPP;
> > +                   goto out;
> > +           }
> > +           async_lock = true;
> > +           unique = req->unique;
> > +           fuse_reply_wait(req);
> > +   }
> >     /* TODO: Is it alright to modify flock? */
> >     lock->l_pid = 0;
> > -   ret = fcntl(plock->fd, F_OFD_SETLK, lock);
> > +   if (async_lock)
> > +           ret = fcntl(ofd, F_OFD_SETLKW, lock);
> > +   else
> > +           ret = fcntl(ofd, F_OFD_SETLK, lock);
> 
> What happens if the guest is rebooted after it's asked
> for, but not been granted a lock?

I think a regular reboot can't be done till a request is pending, because
virtio-fs can't be unmounted and unmount will wait for all pending
requests to finish.

Destroying qemu will destroy deamon too.

Are there any other reboot paths I have missed.

Thanks
Vivek