Re: [LTP] [PATCH] mremap06: fallocate is not supported on nfsv3

[Petr Vorel <pvorel@suse.cz>]

> Hi!
> > > > > -	if (ret == -1)
> > > > > +	if (ret != 0) {
> > > > > +		if (errno == EOPNOTSUPP || errno == ENOSYS) {
> > > > > +			tst_brk(TCONF,
> > > > > +				"fallocate system call is not implemented");
> > > > > +		}
> > > > >   		tst_brk(TBROK, "fallocate() failed");
> > > > > +		return;

> > I suggest to merge this now, without return (it can be removed before merge).
> > Reviewed-by: Petr Vorel <pvorel@suse.cz>

> Shouldn't we limit this only to nfs, to make sure that fallocate() is
> not accidentally disabled on other filesystems? At least that what I
> suggested when I replied to the patch.

That's what I also meant by my earlier suggestion (or, better I was not sure
myself if it's needed). I would vote for this check. But since we already have
this problem in other files, I would be ok to merge this first and handle
proper fix as a separate approach if Samasth does not have time to solve it
himself. @Samasth WDYT?

The solution would be to at least check for tst_fs_type(".") == TST_NFS_MAGIC.
Perfect solution would IMHO be to check for NFS version (e.g. in /proc/mounts)
and TCONF only on NFSv3.

BTW When I first read man fallocate(2), I interpreted following note related to
FALLOC_FL_PUNCH_HOLE about general fallocate() support:

	Not all filesystems support FALLOC_FL_PUNCH_HOLE; if a filesystem doesn't
	support the operation, an error is returned.  The operation is supported on at
	least the following filesystems:

	•  XFS (since Linux 2.6.38)
	•  ext4 (since Linux 3.0)
	•  Btrfs (since Linux 3.7)
	•  tmpfs(5) (since Linux 3.5)
	•  gfs2(5) (since Linux 4.16)

Some of the tests which are using fallocate() indeed test FALLOC_FL_PUNCH_HOLE:

$ git grep -l FALLOC_FL_PUNCH_HOLE testcases/
testcases/kernel/mem/hugetlb/hugefallocate/hugefallocate01.c
testcases/kernel/mem/hugetlb/hugefallocate/hugefallocate02.c
testcases/kernel/syscalls/fallocate/fallocate04.c
testcases/kernel/syscalls/fallocate/fallocate05.c
testcases/kernel/syscalls/fallocate/fallocate06.c
testcases/kernel/syscalls/memfd_create/memfd_create_common.c

and others not, e.g.:
testcases/kernel/syscalls/fallocate/fallocate0[1-3].c
testcases/kernel/syscalls/mremap/mremap06.c (which does not check errno at all,
likely not needed).

Therefore also check for FALLOC_FL_PUNCH_HOLE would be needed (in addition to
all NFS or NFSv3).

BTW the man page does not mention NFS at all. @Samasth would you please send a
patch to linux-man ML?

Kind regards,
Petr

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