Linux Virtualization - Sep 2019 - [PATCH v3 00/13] virtio-fs: shared file system for virtual machines

On Tue, Sep 03, 2019 at 10:07:52AM -0400, Vivek Goyal
wrote:
> On Tue, Sep 03, 2019 at 04:31:38AM -0400, Michael S. Tsirkin wrote:
> 
> [..]
> > +	/* TODO lock */
> > give me pause.
> > 
> > Cleanup generally seems broken to me - what pauses the FS
> 
> I am looking into device removal aspect of it now. Thinking of adding
> a reference count to virtiofs device and possibly also a bit flag to
> indicate if device is still alive. That way, we should be able to cleanup
> device more gracefully.
Generally, the way to cleanup things is to first disconnect device from
linux so linux won't send new requests, wait for old ones to finish.



> > 
> > What about the rest of TODOs in that file?
> 
> I will also take a closer look at TODOs now. Better device cleanup path
> might get rid of some of them. Some of them might not be valid anymore.
> 
> > 
> > use of usleep is hacky - can't we do better e.g. with a
> > completion?
> 
> Agreed.
> 
> Thanks
> Vivek

On Tue, Sep 03, 2019 at 10:12:16AM -0400, Michael S. Tsirkin
wrote:
> On Tue, Sep 03, 2019 at 10:07:52AM -0400, Vivek Goyal wrote:
> > On Tue, Sep 03, 2019 at 04:31:38AM -0400, Michael S. Tsirkin wrote:
> > 
> > [..]
> > > +	/* TODO lock */
> > > give me pause.
> > > 
> > > Cleanup generally seems broken to me - what pauses the FS
> > 
> > I am looking into device removal aspect of it now. Thinking of adding
> > a reference count to virtiofs device and possibly also a bit flag to
> > indicate if device is still alive. That way, we should be able to
cleanup
> > device more gracefully.
> 
> Generally, the way to cleanup things is to first disconnect device from
> linux so linux won't send new requests, wait for old ones to finish.
I was thinking of following.

- Set a flag on device to indicate device is dead and not queue new
  requests. Device removal call can set this flag.

- Return errors when fs code tries to queue new request.

- Drop device creation reference in device removal path. If device is
  mounted at the time of removal, that reference will still be active
  and device state will not be cleaned up in kernel yet.

- User unmounts the fs, and that will drop last reference to device and
  will lead to cleanup of in kernel state of the device.

Does that sound reasonable.

Vivek

On Tue, Sep 03, 2019 at 10:18:51AM -0400, Vivek Goyal
wrote:
> On Tue, Sep 03, 2019 at 10:12:16AM -0400, Michael S. Tsirkin wrote:
> > On Tue, Sep 03, 2019 at 10:07:52AM -0400, Vivek Goyal wrote:
> > > On Tue, Sep 03, 2019 at 04:31:38AM -0400, Michael S. Tsirkin
wrote:
> > > 
> > > [..]
> > > > +	/* TODO lock */
> > > > give me pause.
> > > > 
> > > > Cleanup generally seems broken to me - what pauses the FS
> > > 
> > > I am looking into device removal aspect of it now. Thinking of
adding
> > > a reference count to virtiofs device and possibly also a bit flag
to
> > > indicate if device is still alive. That way, we should be able to
cleanup
> > > device more gracefully.
> > 
> > Generally, the way to cleanup things is to first disconnect device
from
> > linux so linux won't send new requests, wait for old ones to
finish.
> 
> I was thinking of following.
> 
> - Set a flag on device to indicate device is dead and not queue new
>   requests. Device removal call can set this flag.
> 
> - Return errors when fs code tries to queue new request.
> 
> - Drop device creation reference in device removal path. If device is
>   mounted at the time of removal, that reference will still be active
>   and device state will not be cleaned up in kernel yet.
> 
> - User unmounts the fs, and that will drop last reference to device and
>   will lead to cleanup of in kernel state of the device.
> 
> Does that sound reasonable.
> 
> Vivek
Just we aware of the fact that virtio device, all vqs etc
will be gone by the time remove returns.


-- 
MST