linux-kernel - Re: [PATCH v3 00/13] virtio-fs: shared file system for virtual machines

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Date:   Tue, 3 Sep 2019 13:15:16 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     Miklos Szeredi <miklos@...redi.hu>,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        virtio-fs@...hat.com, Stefan Hajnoczi <stefanha@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>
Subject: Re: [PATCH v3 00/13] virtio-fs: shared file system for virtual
 machines

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