Re: [PATCH v2] virtiofs: Export filesystem tags through sysfs

[Vivek Goyal <vgoyal@redhat.com>]

On Sat, Nov 11, 2023 at 06:55:18AM -0500, Greg KH wrote:
> On Wed, Nov 08, 2023 at 04:33:33PM -0500, Vivek Goyal wrote:
> > virtiofs filesystem is mounted using a "tag" which is exported by the
> > virtiofs device. virtiofs driver knows about all the available tags but
> > these are not exported to user space.
> > 
> > People have asked these tags to be exported to user space. Most recently
> > Lennart Poettering has asked for it as he wants to scan the tags and mount
> > virtiofs automatically in certain cases.
> > 
> > https://gitlab.com/virtio-fs/virtiofsd/-/issues/128
> > 
> > This patch exports tags through sysfs. One tag is associated with each
> > virtiofs device. A new "tag" file appears under virtiofs device dir.
> > Actual filesystem tag can be obtained by reading this "tag" file.
> > 
> > For example, if a virtiofs device exports tag "myfs", a new file "tag"
> > will show up here. Tag has a newline char at the end.
> > 
> > /sys/bus/virtio/devices/virtio<N>/tag
> > 
> > # cat /sys/bus/virtio/devices/virtio<N>/tag
> > myfs
> > 
> > Note, tag is available at KOBJ_BIND time and not at KOBJ_ADD event time.
> > 
> > v2:
> > - Add a newline char at the end in tag file. (Alyssa Ross)
> > - Add a line in commit logs about tag file being available at KOBJ_BIND
> >   time and not KOBJ_ADD time.
> > 
> > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > ---
> >  fs/fuse/virtio_fs.c | 34 ++++++++++++++++++++++++++++++++++
> >  1 file changed, 34 insertions(+)
> 
> No documentation for your new sysfs file?  :(

Hi Greg,

My bad. I forgot about it while posting V2.

As per your comment in another email, I will include some documentation
in Documentation/ABI/. Not very sure what file name to choose. I will
probably start with "sysfs-bus-virtio-devices-virtiofs".

Thanks
Vivek