Re: [PATCH v2] generic/402: Make timestamp range check conditional

[Eryu Guan <guaneryu@gmail.com>]

On Wed, Jan 08, 2020 at 10:45:29AM +0200, Amir Goldstein wrote:
> On Wed, Jan 8, 2020 at 10:09 AM Eryu Guan <guaneryu@gmail.com> wrote:
> >
> > On Mon, Dec 30, 2019 at 09:34:47AM +0200, Amir Goldstein wrote:
> > > On Sun, Dec 29, 2019 at 12:13 AM Deepa Dinamani <deepa.kernel@gmail.com> wrote:
> > > >
> > > > Addition of fs-specific timestamp range checking was added
> > > > in 188d20bcd1eb ("vfs: Add file timestamp range support").
> > > >
> > > > Add a check for whether the kernel supports the limits check
> > > > before running the associated test.
> > > >
> > > > ext4 has been chosen to test for the presence of kernel support
> > > > for this feature. If there is a concern that ext4 could be built
> > > > out of the kernel, I can include a _require_ext4() along the
> > > > lines of _require_ext2().
> > > >
> > > > Suggested-by: Amir Goldstein <amir73il@gmail.com>
> > > > Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
> >
> > Sorry for chiming in so late..
> >
> > > > ---
> > > > * Changes since v1:
> > > >   used loopback device instead of mkfs scratch dev
> > > >
> > > >  common/rc         | 26 ++++++++++++++++++++++++++
> > > >  tests/generic/402 |  3 +++
> > > >  2 files changed, 29 insertions(+)
> > > >
> > > > diff --git a/common/rc b/common/rc
> > > > index 816588d6..6248adf7 100644
> > > > --- a/common/rc
> > > > +++ b/common/rc
> > > > @@ -1981,6 +1981,32 @@ _run_aiodio()
> > > >      return $status
> > > >  }
> > > >
> > > > +_require_kernel_timestamp_range()
> > > > +{
> > > > +       LOOP_FILE=$SCRATCH_MNT/loop_file
> > > > +       LOOP_MNT=$SCRATCH_MNT/loop_mnt
> > > > +
> > > > +       dd if=/dev/zero of=$LOOP_FILE bs=1M count=2 2>&1 | _filter_dd || _fail "loopback prep failed"
> > > > +
> > > > +       # Use ext4 with 128-byte inodes, which do not have room for extended timestamp
> > > > +       FSTYP=ext4 MKFS_OPTIONS=-I128 \
> > > > +       _mkfs_dev $LOOP_FILE >> $seqres.full 2>&1 || _fail "ext4 mkfs failed"
> > > > +
> > > > +       LOOP_DEV=$(_create_loop_device $LOOP_FILE)
> > > > +       mkdir -p $LOOP_MNT >> $seqres.full 2>&1 || _fail "failed to create $LOOP_MNT"
> > > > +       mount -t ext4 ${LOOP_DEV} ${LOOP_MNT} >> $seqres.full 2>&1 || _fail "ext4 mount failed"
> > > > +       notrun=false
> > > > +       _check_dmesg_for "ext4 filesystem being mounted at ${LOOP_MNT} supports timestamps until 2038" || \
> > > > +               notrun=true
> > > > +
> > > > +       umount ${LOOP_MNT} >> $seqres.full 2>&1 ||_fail "failed to umount $LOOP_MNT"
> > > > +       _destroy_loop_device ${LOOP_DEV} >> $seqres.full 2>&1
> > > > +
> > > > +       if $notrun; then
> > > > +               _notrun "Kernel does not support timestamp limits"
> > > > +       fi
> > > > +}
> > > > +
> > >
> > > As a generic helper, this function has a few problems:
> > > 1. It assumes scratch dev is mounted (and you're not even calling it
> > > after _scratch_mount)
> > > 2. The cleanup() hook won't clean loop mnt/dev if interrupted
> > > 3. test doesn't have _require_loop (nor require ext4 as you mentioned)
> > >
> > > All this leads me to think that perhaps it would be better off, at least until
> > > kernel has fsinfo, to keep this entire helper inside generic/402,
> > > while addressing
> > > the issues above in the test itself.
> > >
> > > A more generic solution would be harder and IMO and overkill at this point.
> > >
> > > What do you think?
> >
> > After reading through this thread, I prefer waiting for the comming
> > fsinfo interface, detecting the timestamp limit support using ext2 &
> > loop device doesn't look "pretty" and is just a temporary solution.
> >
> 
> I understand why you dislike the ext2+loop test, but please hear me out.
> 
> From all the fs types that are supported by the test, only btrfs and ext4 with
> large inode size are y2038 ready.
> For the rest of the cases, we actually have a way to detect kernel support
> from the dmesg warning, without the need for hacky ext2 loop mount.
> 
> So how about just:
> 1. moving  _scratch_mount before _require_timestamp_range
> 2. in _require_timestamp_range (untested):
>         if [ $tsmax -lt $((1<<32)) ] && ! _check_dmesg_for "supports

Yeah, this looks fine. I thought about searching for dmesg warning after
_scratch_mount as well, but that would _notrun if the fs is 2038-safe.
This $tsmax check fixes my concern. Thanks!

Eryu

> timestamps until 2038" ; then
>                 _notrun "Kernel does not support timestamp limits"
>         fi
> 
> It's better than nothing and it does not add much complications, nor
> is this "hacky"
> IMO.
> 
> Thoughts?
> 
> Amir.