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

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

[Jan Polensky]

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");
 	}
-- 
2.54.0


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Re: [LTP] swap: Add exfat to filesystems requiring tst_fill_file

[linuxtestproject.agent]

Hi Jan,

On 08 Jun 2026, Jan Polensky wrote:
> swap: Add exfat to filesystems requiring tst_fill_file

Verdict: Reviewed

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Note:

The agent can sometimes produce false positives although often its
findings are genuine. If you find issues with the review, please
comment this email or ignore the suggestions.

Regards,
LTP AI Reviewer

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

[Cyril Hrubis]

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");
>  	}

The swapon01 works for me for exfat without this change. Where does this
fail (arch, kernel, OS, is exfat in kernel or FUSE, etc.)?

-- 
Cyril Hrubis
chrubis@suse.cz

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Re: [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

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

[Andrea Cervesato via ltp]

Hi Jan,

maybe I reproduced it, but it would be nice to have the test output
as well. Also Kernel 7.1 is still in RC stage, so this patch must
wait kernel release before being considered valid.

The next time please add more information to the commit, so we know
exactly what kernel version is having issues, as well as the arch
and distro.


Regards,
--
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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

[Cyril Hrubis]

Hi!
> maybe I reproduced it, but it would be nice to have the test output
> as well. Also Kernel 7.1 is still in RC stage, so this patch must
> wait kernel release before being considered valid.

If it's reproducible only in 7.1 isn't it a kernel regression?

-- 
Cyril Hrubis
chrubis@suse.cz

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

[Andrea Cervesato via ltp]

Hi Cyril,

> > maybe I reproduced it, but it would be nice to have the test output
> > as well. Also Kernel 7.1 is still in RC stage, so this patch must
> > wait kernel release before being considered valid.
> 
> If it's reproducible only in 7.1 isn't it a kernel regression?

Had time to go back looking at the results. Error was caused by an
another issue on my side. I also can't reprouce the issue on kernel
7.1.0 after the release. I ran swapon01, but it runs fine.

Regards,
--
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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

[Andrea Cervesato via ltp]

An update. I had to go through the code to understand if we are having
issues from our side. Indeed, there's a commit which is responsible for
this exfat behaviour and it's causing a regression-like issue:

bf1797960c20 - exfat: add fallocate FALLOC_FL_ALLOCATE_RANGE support

tst_prealloc_size_fd() is called by make_swapfile() which is called by our
swapon/swapoff testing suites. Inside it we use fallocate() that is now
supported by exfat and returns 0 after the kernel patch.

This naturally falls down into the next:

	/* Fill the file if needed (specific to old xfs filesystems) */
	if (tst_fs_type(swapfile) == TST_XFS_MAGIC) {
		if (tst_fill_file(swapfile, 0, blk_size, blocks) != 0)
			tst_brk_(file, lineno, TBROK, "Failed to fill swapfile");
	}

but there's no data written and we get EINVAL at the end of the tests
because swapon() is using a file created with fallocate() instead.

The Jan assumption is correct and the patch as well, but it's strange
we can't reproduce it. The EINVAL is the expected behaviour in this case.

I'm just wondering how to implement it better.

First of all, we should mention the commit that introduced fallocate()
support into exfat inside the patch commit message.

Secondly, since the code was already working before v7.1, maybe we should
fill the file in exfat only for kernel >= 7.1. But I don't want to touch
the core library.

@Cyril WDYT?

Regards,
--
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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

[Andrea Cervesato via ltp]

> I'm just wondering how to implement it better.
> 
> First of all, we should mention the commit that introduced fallocate()
> support into exfat inside the patch commit message.
> 
> Secondly, since the code was already working before v7.1, maybe we should
> fill the file in exfat only for kernel >= 7.1. But I don't want to touch
> the core library.

Second update: .swap_activate is not implemented in the linux kernel
for exfat and the commit causes EINVAL only for swap allocation. That
is caused by bmap() due to the generic swap activation.

So instead of working around the issue, we probably should have a feature
in the kernel along with fallocate() support in exfat.

Probably a kernel bug/missing feature.

--
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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