[Virtio-fs] [virtio-dev] [PATCH v2 0/2] virtio-fs: add notification queue

[Vivek Goyal]

On Thu, May 13, 2021 at 02:44:42PM +0100, Stefan Hajnoczi wrote:
> On Thu, May 13, 2021 at 06:36:37AM +0800, Liu Bo wrote:
> > Hi Stefan,
> > 
> > On Tue, May 11, 2021 at 09:22:24AM +0100, Stefan Hajnoczi wrote:
> > > On Mon, Feb 15, 2021 at 09:54:08AM +0000, Stefan Hajnoczi wrote:
> > > > v2:
> > > >  * Document empty virtqueue behavior for FUSE_NOTIFY_LOCK messages
> > > > 
> > > > This patch series adds the notification queue to the VIRTIO specification.
> > > > This new virtqueue carries device->driver FUSE notify messages.  They are
> > > > currently unused but will be necessary for file locking, which can block for an
> > > > unbounded amount of time and therefore needs a asynchronous completion event
> > > > instead of a request/response buffer that consumes space in the request
> > > > virtqueue until the operation completes.
> > > > 
> > > > Patch 1 corrects an oversight I noticed: the file system device was not added
> > > > to the Conformance chapter.
> > > > 
> > > > Stefan Hajnoczi (2):
> > > >   virtio-fs: add file system device to Conformance chapter
> > > >   virtio-fs: add notification queue
> > > > 
> > > >  conformance.tex | 23 ++++++++++++++++
> > > >  virtio-fs.tex   | 71 ++++++++++++++++++++++++++++++++++++++++++-------
> > > >  2 files changed, 84 insertions(+), 10 deletions(-)
> > > 
> > > Reminder to anyone who needs the virtio-fs notification queue: please
> > > review this series.
> > >
> > 
> > Besides using notification queue to provide posix lock support, I've
> > also managed to invalidate dentry/inode's cache with notification
> > queue, it worked well.
> 
> Thank you!
> 
> Are you using dentry/inode cache invalidation to reduce the number of
> file descriptors that virtiofsd needs to hold open,

Using notifications to invalidate client's dentry/inode cache sounds
interesting. Will like to see an actual implementation though. Various
races w.r.t opening the same file for which server is trying to invalidate
the dentry/inode might be little tricky.

Thanks
Vivek