Messages in this thread | | | Date | Fri, 21 May 2021 10:39:21 +0200 | From | Greg Kurz <> | Subject | Re: [PATCH v4 4/5] virtiofs: Skip submounts in sget_fc() |
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On Fri, 21 May 2021 10:26:27 +0200 Miklos Szeredi <miklos@szeredi.hu> wrote:
> On Thu, 20 May 2021 at 17:47, Greg Kurz <groug@kaod.org> wrote: > > > > All submounts share the same virtio-fs device instance as the root > > mount. If the same virtiofs filesystem is mounted again, sget_fc() > > is likely to pick up any of these submounts and reuse it instead of > > the root mount. > > > > On the server side: > > > > # mkdir ${some_dir} > > # mkdir ${some_dir}/mnt1 > > # mount -t tmpfs none ${some_dir}/mnt1 > > # touch ${some_dir}/mnt1/THIS_IS_MNT1 > > # mkdir ${some_dir}/mnt2 > > # mount -t tmpfs none ${some_dir}/mnt2 > > # touch ${some_dir}/mnt2/THIS_IS_MNT2 > > > > On the client side: > > > > # mkdir /mnt/virtiofs1 > > # mount -t virtiofs myfs /mnt/virtiofs1 > > # ls /mnt/virtiofs1 > > mnt1 mnt2 > > # grep virtiofs /proc/mounts > > myfs /mnt/virtiofs1 virtiofs rw,seclabel,relatime 0 0 > > none on /mnt/mnt1 type virtiofs (rw,relatime,seclabel) > > none on /mnt/mnt2 type virtiofs (rw,relatime,seclabel) > > > > And now remount it again: > > > > # mount -t virtiofs myfs /mnt/virtiofs2 > > # grep virtiofs /proc/mounts > > myfs /mnt/virtiofs1 virtiofs rw,seclabel,relatime 0 0 > > none on /mnt/mnt1 type virtiofs (rw,relatime,seclabel) > > none on /mnt/mnt2 type virtiofs (rw,relatime,seclabel) > > myfs /mnt/virtiofs2 virtiofs rw,seclabel,relatime 0 0 > > # ls /mnt/virtiofs2 > > THIS_IS_MNT2 > > > > Submount mnt2 was picked-up instead of the root mount. >
> Why is this a problem? >
It seems very weird to mount the same filesystem again and to end up in one of its submounts. We should have:
# ls /mnt/virtiofs2 mnt1 mnt2
> Thanks, > Miklos
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