[LTP] [PATCH v1 1/1] swap: Add exfat to filesystems requiring tst_fill_file

[Jan Polensky]

On Tue, Jun 09, 2026 at 11:19:19AM +0200, Cyril Hrubis wrote:
> Hi!
> > exfat, like XFS, requires actual data writes (not just fallocate) to
> > fully allocate swap files. Without this, swapon(2) fails with EINVAL
> > due to unallocated extents.
> >
> > This matches the kernel's requirement that swap files must be fully
> > allocated before activation.
> >
> > Signed-off-by: Jan Polensky <japo@linux.ibm.com>
> > ---
> >  libs/swap/tse_swap.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/libs/swap/tse_swap.c b/libs/swap/tse_swap.c
> > index ae3c193132e6..e321cb1dfe63 100644
> > --- a/libs/swap/tse_swap.c
> > +++ b/libs/swap/tse_swap.c
> > @@ -177,8 +177,9 @@ int make_swapfile(const char *file, const int lineno,
> >  	if (prealloc_contiguous_file(swapfile, blk_size, blocks) != 0)
> >  		tst_brk_(file, lineno, TBROK, "Failed to create swapfile");
> >
> > -	/* Fill the file if needed (specific to old xfs filesystems) */
> > -	if (tst_fs_type(swapfile) == TST_XFS_MAGIC) {
> > +	/* Fill the file if needed (specific to xfs and exfat filesystems) */
> > +	long fs_type = tst_fs_type(swapfile);
> > +	if (fs_type == TST_XFS_MAGIC || fs_type == TST_EXFAT_MAGIC) {
> >  		if (tst_fill_file(swapfile, 0, blk_size, blocks) != 0)
> >  			tst_brk_(file, lineno, TBROK, "Failed to fill swapfile");
> >  	}
>
Hi Cyril,
> The swapon01 works for me for exfat without this change. Where does this
> fail (arch, kernel, OS, is exfat in kernel or FUSE, etc.)?

The failure occurred on:
 - Architecture: s390x
 - Kernel: 7.1.0-20260608.rc7.git374.a87737435cfa.300.fc44.s390x+next
   (linux-next and since ~ 17 days)
 - OS: Fedora Linux 44
 - exfat: Kernel module (not FUSE)

The issue manifests when swapon(2) is called on an exfat swap file that was
created using only fallocate() without actual data writes. The kernel rejects
the swap file with EINVAL because it detects unallocated extents.

This is similar to the existing XFS behavior where tst_fill_file() is already
required. Both filesystems need actual data writes (not just metadata
allocation via fallocate) to ensure swap files are fully allocated before
swapon(2) can activate them.

The patch ensures consistent behavior across filesystems that have this
requirement.

Best regards,
Jan
>
> --
> Cyril Hrubis
> chrubis@suse.cz