On Wed, Nov 25, 2020 at 04:03:06PM +0200, Amir Goldstein wrote:
> On Wed, Nov 25, 2020 at 12:46 PM Sargun Dhillon <sargun@xxxxxxxxx> wrote:
> >
> > Volatile remounts validate the following at the moment:
> > * Has the module been reloaded / the system rebooted
> > * Has the workdir been remounted
> >
> > This adds a new check for errors detected via the superblock's
> > errseq_t. At mount time, the errseq_t is snapshotted to disk,
> > and upon remount it's re-verified. This allows for kernel-level
> > detection of errors without forcing userspace to perform a
> > sync and allows for the hidden detection of writeback errors.
> >
>
> Looks fine as long as you verify that the reuse is also volatile.
>
> Care to also add the alleged issues that Vivek pointed out with existing
> volatile mount to the documentation? (unless Vivek intends to do fix those)
I thought current writeback error issue with volatile mounts needs to
be fixed with shutting down filesystem. (And mere documentation is not
enough).
Amir, are you planning to improve your ovl-shutdown patches to detect
writeback errors for volatile mounts. Or you want somebody else to
look at it.
W.r.t this patch set, I still think that first we should have patches
to shutdown filesystem on writeback errors (for volatile mount), and
then detecting writeback errors on remount makes more sense.
Vivek
>
> > Signed-off-by: Sargun Dhillon <sargun@xxxxxxxxx>
> > ---
> > fs/overlayfs/overlayfs.h | 1 +
> > fs/overlayfs/readdir.c | 6 ++++++
> > fs/overlayfs/super.c | 1 +
> > 3 files changed, 8 insertions(+)
> >
> > diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> > index de694ee99d7c..e8a711953b64 100644
> > --- a/fs/overlayfs/overlayfs.h
> > +++ b/fs/overlayfs/overlayfs.h
> > @@ -85,6 +85,7 @@ struct ovl_volatile_info {
> > */
> > uuid_t ovl_boot_id; /* Must stay first member */
> > u64 s_instance_id;
> > + errseq_t errseq; /* Implemented as a u32 */
> > } __packed;
> >
> > /*
> > diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
> > index 4e3e2bc3ea43..2bb0641ecbbd 100644
> > --- a/fs/overlayfs/readdir.c
> > +++ b/fs/overlayfs/readdir.c
> > @@ -1109,6 +1109,12 @@ static int ovl_verify_volatile_info(struct ovl_fs *ofs,
> > return -EINVAL;
> > }
> >
> > + err = errseq_check(&volatiledir->d_sb->s_wb_err, info.errseq);
> > + if (err) {
> > + pr_debug("Workdir filesystem reports errors: %d\n", err);
> > + return -EINVAL;
> > + }
> > +
> > return 1;
> > }
> >
> > diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> > index 9a1b07907662..49dee41ec125 100644
> > --- a/fs/overlayfs/super.c
> > +++ b/fs/overlayfs/super.c
> > @@ -1248,6 +1248,7 @@ static int ovl_set_volatile_info(struct ovl_fs *ofs, struct dentry *volatiledir)
> > int err;
> > struct ovl_volatile_info info = {
> > .s_instance_id = volatiledir->d_sb->s_instance_id,
> > + .errseq = errseq_sample(&volatiledir->d_sb->s_wb_err),
> > };
> >
> > uuid_copy(&info.ovl_boot_id, &ovl_boot_id);
> > --
> > 2.25.1
> >
>
