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Wong via Linux-f2fs-devel" Reply-To: "Darrick J. Wong" Cc: hch@infradead.org, zlang@redhat.com, fstests@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On Wed, Jul 22, 2026 at 06:36:13AM +0800, Anand Suveer Jain wrote: > > > > This is where I continue getting stuck on this patchset -- fsid is so > > poorly defined that I don't think the rest of these fsid tests make > > sense at all. Nobody mandates that fsid is persistent or stable across > > remounts. Nobody even mandates that two cloned filesystems don't have > > the same fsid value. > > > > The statfs manpage says: > > > > "Nobody knows what f_fsid is supposed to contain (but see below)" > > > > and then: > > > > "The general idea is that f_fsid contains some random stuff such that > > the pair (f_fsid,ino) uniquely determines a file." > > Which is exactly why we need fstests guardrails. > Keeps filesystem's implementation consistent across kernel versions. > Embarrassingly, I introduced a bug around this that is now fixed. > The commit IDs are in the test cases. > Thus motivation for this fstests patch. > > > Based on that very weak statement, at most it might make sense to check > > that two separate and simultaneously mounted filesystems don't end up > > with the same fsid > > Yes, for xfs, btrfs and f2fs. However for ext4 cloned filesystems can > share the same fsid and ino because the images are identical. > It is then up to the usecase to change the UUID for either filesystem if > it gets modified. > Commit ("fstests: add _require_unique_f_fsid() helper") captures this, > and the link in that commit includes the discussion. > > > just in case there *are* programs foolish enough to > > use (fsid,ino) as a uniqueness check. > > On the other hand, if a program needs a unique ID, do we currently have > any way to get one? I don't think there is a way to get a globally unique identifier for a filesystem image except for the meta_uuid filesystems, and even then only if the volume manager resets the user-visible uuid every time it makes a clone and nobody runs a duplicator. --D > Thanks, Anand > > > _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel