Re: [LTP] [PATCH 0/3] tst_device: add support for overlayfs

[Petr Vorel <pvorel@suse.cz>]

Hi Jeff, all,

NOTE: 'rm -fv lib/libltp.a' is required to apply the patchset.

Besides it, it does not compile yet:
/usr/bin/ld: cannot find -lltp: No such file or directory
https://lore.kernel.org/ltp/20250207112353.GA1739723@pevik/

> When running ltp-aiodio on an overlay file system, the following error
> occurs:

> tst_tmpdir.c:316: TINFO: Using /mnt/fstests/TEST_DIR/ovl-mnt/ltp-hSHEHy5M0s/LTP_aio4q4GMW as tmpdir (overlayfs filesystem)
> tst_test.c:1888: TINFO: LTP version: 20220121-2271-g91a10df22
> tst_test.c:1892: TINFO: Tested kernel: vendor kernel
> tst_test.c:1723: TINFO: Timeout per run is 0h 40m 00s
> aiocp.c:211: TINFO: Maximum AIO blocks: 65536
> tst_device.c:551: TINFO: Use BTRFS specific strategy
> tst_device.c:569: TBROK: BTRFS ioctl failed. Is . on a tmpfs?: ENOTTY (25)

> The issue is that stat(2) on an overlayfs mount point will return a
> major device number of 0.  The code assumes this is btrfs, and tries
> to issue a btrfs-specific ioctl.  When that fails, the final message is
> printed that suggests this might be tmpfs.

> I modified the code to use statfs(2) to get the file system type, and
> use that to determine which file system specific code to call.  Finally, I
> added code to parse out the upper directory from the overlayfs mount options
> using libmount.  libmount is part of util-linux, so it should be fairly

We try to avoid external libraries to help testing kernel on some minimal
embedded devices. @Cyril: is it ok to drag libmount-devel?

@Jeff: would it be too hard to parse /proc/self/mountinfo (I suppose
/proc/self/mounts is not enough)? I'm looking into libmount code E.e.
mnt_fs_get_option() [1]. Or do you think it would be too fragile to parse it
without libmount?

Kind regards,
Petr

[1] https://git.kernel.org/pub/scm/utils/util-linux/util-linux.git/tree/libmount/src/fs.c#n1568

> ubiquitous.  stat(2) is then called on the upper directory to get to the
> underlying device node.

> Review of the series is greatly appreciated.

> Thanks in advance!
> Jeff

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