Re: [PATCH v3] fstests: generic: add a test case to check fsverity reads

[Qu Wenruo <wqu@suse.com>]

在 2026/10/16 18:17, Eric Biggers 写道:
> On Mon, Oct 12, 2026 at 08:56:13AM +1030, Qu Wenruo wrote:
>> +_fixed_by_fs_commit btrfs xxxxxxxxxxxx \
>> +	"btrfs: fix the fsverity callback where unexpected range is verified"
> 
> Even without that commit, 'kvm-xfstests -c btrfs generic/807' still
> passes.  Under what circumstances will this test fail?

It need as least 7.2 upstream, which enables large data folios for btrfs 
by default.

And I can always reproduce it here, mind to provide more info about the 
passed run?

> 
>> +# Read the file, unpatched btrfs will verify blocks outside the read range and
>> +# trigger fs-verity warnings.
>> +# But the read itself should still be fine, as the failed part will be retried.
>> +cat "$SCRATCH_MNT/foobar" > /dev/null
> 
> How about using md5sum and putting the expected value in the .out file,
> so the contents are validated too?

That won't catch the problem.

The root problem is that, for a large folio, a read bio can only cover 
part of the folio.
And at end io time, unpatched btrfs call fsverity_verify_folio() which 
can have data that is still under read, thus fsverity will report errors.
However after each read, the correct data are already copied into the 
page cache.

So after a fsverity verification failure, MM/VFS will retry the read, 
and since other parts may have already copied the correct data into page 
cache, eventually the incorrect fsverity_verify_folio() will succeed, 
thus no read error is returned to the user space.

So md5sum will always be correct.

> 
>> +# Check for any kernel warnings from fs-verity on file corruption.
>> +if _check_dmesg_for "FILE CORRUPTED!"; then
>> +	echo "fs-verity detected corruption"
>> +fi
> 
> Is there a way to use the fserror support being added by
> https://lore.kernel.org/fsverity/20261002223705.2175542-2-aalbersh@kernel.org/
> instead of relying on the unstable text printed to the kernel log?  If
> the string is changed at all, this test will become ineffective.

That's a better idea, I'll need to check if it's possible grab fserror 
info from btrfs.

Thanks,
Qu

> 
> - Eric