Re: [PATCH] generic/492: bypass the blkid cache when probing the label

["Theodore Tso" <tytso@mit.edu>]

On Mon, Sep 21, 2026 at 04:49:10PM -0500, Darrick J. Wong wrote:
> > The difference between the e2fsprogs and util-linux libblkid is the
> > time granularity: the former stores seconds only (TIME="%ld",
> > bid_time = time(0), compares st_mtime <= bid_time), while the latter
> > stores usec (TIME="sec.usec") and has an nsec tie-break in the compare,
> > so the same-second case is much easier to hit with the e2fsprogs blkid.
> 
> Perhaps xfstests-bld should use the system blkid then?  IIRC the one
> in e2fsprogs is very old and out of date.

Historically, xfstests-bld was built in environments where libblkid
wasn't available.  This included Android's runtime (which uses the
bionic libc), and grte (Google Runtime Environment)[1].

[1] https://github.com/bazelment/lrte/blob/master/grte/grte-build

However, as more and more tests require utilities from util-linux,
xfstests-bld was taught to build util-linux.  And if util-linux is
being built, then we don't use e2fsprogs-libs any more, which is where
libblkid is built.  From build-all:

if test -z "$USE_LOCAL_E2FSLIBS" -o -d util-linux; then
    SKIP_E2FSLIBS=yes
fi

I've always built xfstesets-bld with util-linux, even though it is
listed as an optional repository.  This is because (a) util-linux is
needed for Android and other non-standard Linux environments, and (b)
the version of util-linux used by earlier Debian Stable was too old
for some of the newer tests in fstests and blktests.

If you aren't building xfstests-bld with util-linux, it falls back to
building libblkid from e2fsprogs-libs.  HOWEVER, we don't actually
blkid, and libblkid is always built statically.  So what seems to be
going on is that one of the programs built by xfstests-bld is using
the older libblkid, and that results in the blkid cache being writen
with a second granularity.

I've never noticed this issue because I've always built with
util-linux.  The way to solve this is to require building with the
system libblkid if util-linux is not being built, and to drop
e2fsprogs-libs from xfstests-bld.  Or just build xfstests-bld with
util-linux.  :-)

Cheers,

					- Ted