[LTP] [PATCH v17] fsconfig04: Check FSCONFIG_SET_PATH

[Cyril Hrubis]

On Wed, Oct 21, 2026 at 08:49:12AM +0000, Wei Gao via ltp wrote:
> The fsconfig01.c does not test if FSCONFIG_SET_PATH has any effect;
> most of the calls there just set a dummy "sync" parameter. This test
> case aims to verify if the FSCONFIG_SET_PATH operation can be used
> to dynamically change the external journal device of an ext3 or ext4
> filesystem.
> 
> Closes: https://github.com/linux-test-project/ltp/issues/1169
> Signed-off-by: Wei Gao <wegao@suse.com>
> Reviewed-by: Petr Vorel <pvorel@suse.cz>
> ---
>  runtest/syscalls                              |   1 +
>  testcases/kernel/syscalls/fsconfig/.gitignore |   1 +
>  .../kernel/syscalls/fsconfig/fsconfig04.c     | 169 ++++++++++++++++++
>  3 files changed, 171 insertions(+)
>  create mode 100644 testcases/kernel/syscalls/fsconfig/fsconfig04.c
> 
> diff --git a/runtest/syscalls b/runtest/syscalls
> index 2bdb4a9a2..1903f1ac6 100644
> --- a/runtest/syscalls
> +++ b/runtest/syscalls
> @@ -452,6 +452,7 @@ fremovexattr02 fremovexattr02
>  fsconfig01 fsconfig01
>  fsconfig02 fsconfig02
>  fsconfig03 fsconfig03
> +fsconfig04 fsconfig04
>  
>  fsmount01 fsmount01
>  fsmount02 fsmount02
> diff --git a/testcases/kernel/syscalls/fsconfig/.gitignore b/testcases/kernel/syscalls/fsconfig/.gitignore
> index cfedae5f7..bd3754c34 100644
> --- a/testcases/kernel/syscalls/fsconfig/.gitignore
> +++ b/testcases/kernel/syscalls/fsconfig/.gitignore
> @@ -1,3 +1,4 @@
>  /fsconfig01
>  /fsconfig02
>  /fsconfig03
> +/fsconfig04
> diff --git a/testcases/kernel/syscalls/fsconfig/fsconfig04.c b/testcases/kernel/syscalls/fsconfig/fsconfig04.c
> new file mode 100644
> index 000000000..bd649717e
> --- /dev/null
> +++ b/testcases/kernel/syscalls/fsconfig/fsconfig04.c
> @@ -0,0 +1,169 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (c) 2026 Wei Gao <wegao@suse.com>
> + */
> +
> +/*\
> + * This test aims to validate :manpage:`fsconfig(2)` with the
> + * ``FSCONFIG_SET_PATH`` operation in dynamically altering the external
> + * journal device of an ext3 or ext4 filesystem.
> + *
> + * Root privileges are required because the test creates and formats loop
> + * devices, and configures filesystems.
> + *
> + * [Algorithm]
> + *
> + * - Acquire three loop devices (``tst_device->dev`` from framework, ``dev1``, ``dev2``).
> + * - Format ``dev1`` and ``dev2`` as external journal devices with the same UUID
> + *   (``-O journal_dev -U <uuid>``).
> + * - Format ``tst_device->dev`` three times to cycle journal associations:
> + *   ``dev1`` -> ``dev2`` -> ``dev1``, so both journal superblocks are consistent.
> + * - Open ``tst_device->dev`` via :manpage:`fsopen(2)` and set the source and journal_path using
> + *   :manpage:`fsconfig(2)` (``FSCONFIG_SET_STRING``) and
> + *   :manpage:`fsconfig(2)` (``FSCONFIG_SET_PATH``).
> + * - Apply ``FSCONFIG_CMD_CREATE`` and verify with ``tune2fs`` that ``tst_device->dev``'s
> + *   journal device is now ``dev2``.
> + *
> + * Implementation notes:
> + *
> + * - To avoid ``journal UUID does not match`` error when switching external
> + *   journal device, we have to assign the same UUID to ``dev1``/``dev2``.
> + * - Before the :manpage:`fsconfig(2)` test, we have to format ``tst_device->dev`` associating to
> + *   ``dev1`` -> ``dev2`` -> ``dev1``. This ensures that both ``dev1``/``dev2`` superblocks contain
> + *   correct content. Otherwise, you will encounter errors such as
> + *   ``EXT4-fs (loop0): External journal has more than one user (unsupported)``
> + *   when switching the external journal device using :manpage:`fsconfig(2)`.
> + */
> +
> +#include <stdbool.h>
> +#include <sys/stat.h>
> +#include <sys/sysmacros.h>
> +#include "tst_test.h"
> +#include "tst_safe_stdio.h"
> +#include "lapi/fsmount.h"
> +
> +#define LOOP_DEV_SIZE 10
> +#define UUID "d73c9e5e-97e4-4a9c-b17e-75a931b02660"
> +
> +static int fd = -1;
> +static char dev1[PATH_MAX];
> +static char dev2[PATH_MAX];
> +
> +static const char *const mkfs_opts_set_UUID[] = {"-F", "-U", UUID, "-O", "journal_dev", NULL};
> +
> +static void cleanup(void)
> +{
> +	if (fd != -1)
> +		SAFE_CLOSE(fd);
> +
> +	if (dev1[0])
> +		tst_detach_device(dev1);
> +
> +	if (dev2[0])
> +		tst_detach_device(dev2);
> +}
> +
> +static void create_and_attach_loopdev(const char *filename, char *dev_path, size_t dev_path_len)
> +{
> +	if (tst_prealloc_file(filename, 1024 * 1024, LOOP_DEV_SIZE))
> +		tst_brk(TBROK, "Failed to create %s", filename);
> +
> +	if (tst_find_free_loopdev(dev_path, dev_path_len) == -1)
> +		tst_brk(TBROK, "No free loop device found for %s", filename);
> +
> +	if (tst_attach_device(dev_path, filename))
> +		tst_brk(TBROK, "Failed to attach %s to %s", filename, dev_path);
> +}
> +
> +static void format_journal_device(const char *dev, const char *journal)
> +{
> +	char journal_opt[PATH_MAX + 16];
> +	const char *const opts[] = {"-F", "-J", journal_opt, NULL};
> +
> +	snprintf(journal_opt, sizeof(journal_opt), "device=%s", journal);
> +	SAFE_MKFS(dev, tst_device->fs_type, opts, NULL);
> +}
> +
> +static void setup(void)
> +{
> +	fsopen_supported_by_kernel();
> +
> +	create_and_attach_loopdev("dev1_file", dev1, sizeof(dev1));
> +	create_and_attach_loopdev("dev2_file", dev2, sizeof(dev2));
> +}
> +
> +static void run(void)
> +{
> +	/* Reset dev1, dev2 and tst_device->dev superblocks before each test run iteration */
> +	SAFE_MKFS(dev1, tst_device->fs_type, mkfs_opts_set_UUID, NULL);
> +	SAFE_MKFS(dev2, tst_device->fs_type, mkfs_opts_set_UUID, NULL);
> +	format_journal_device(tst_device->dev, dev1);
> +	format_journal_device(tst_device->dev, dev2);
> +	format_journal_device(tst_device->dev, dev1);

I do not get why we have the dev1 and what errors are we working around
here. The dev1 is not used for anything, just formatted again and again.


-- 
Cyril Hrubis
chrubis@suse.cz