Re: [PATCH] selftests/fuse: add the missing symlink caching test

[Luis Henriques <luis@igalia.com>]

On Mon, Oct 26 2026, Sasha Levin wrote:

> Commit 3e14f079d7a0 ("selftests/fuse: add fuse symlink caching test")
> registered fuse_symlink_cache_test in the fuse selftest Makefile and
> .gitignore, but the test source was not part of the applied commit, so
> building the fuse selftests fails:
>
>   make[1]: *** No rule to make target 'fuse_symlink_cache_test.c', needed by '.../fuse_symlink_cache_test'.
>
> Add fuse_symlink_cache_test.c as posted in Luis Henriques's v5
> submission. The test serves a file and a symlink to it from a libfuse
> low-level filesystem, resolves the symlink 100 times, and counts the
> readlink requests that reach the server: one when FUSE_CAP_CACHE_SYMLINKS
> is set during FUSE_INIT, and all 100 when it is not.
>
> Fixes: 3e14f079d7a0 ("selftests/fuse: add fuse symlink caching test")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/r/202610170822.oEJ1Autq-lkp@intel.com/
> Link: https://lore.kernel.org/r/20261001164916.15311-8-luis@igalia.com
> Originally-by: Luis Henriques <luis@igalia.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> As with e64a46aefc01 ("selftests/fuse: add the missing FUSE_HAS_SYNCFS
> privilege test"), the new file in the posted patch is not in the applied
> commit; the other files did land.

Oh, wow!  I wonder how that happen.  Anyway, thanks for noticing that and
for fixing it, Sasha.  If it makes any sense (I wrote the test! :-) ) feel
free to add my

Reviewed-by: Luis Henriques <luis@igalia.com>

Cheers,
-- 
Luís


>  .../fuse/fuse_symlink_cache_test.c            | 162 ++++++++++++++++++
>  1 file changed, 162 insertions(+)
>  create mode 100644 tools/testing/selftests/filesystems/fuse/fuse_symlink_cache_test.c
>
> diff --git a/tools/testing/selftests/filesystems/fuse/fuse_symlink_cache_test.c b/tools/testing/selftests/filesystems/fuse/fuse_symlink_cache_test.c
> new file mode 100644
> index 0000000000000..7b53734995736
> --- /dev/null
> +++ b/tools/testing/selftests/filesystems/fuse/fuse_symlink_cache_test.c
> @@ -0,0 +1,162 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Simple filesystem to test FUSE symlink cache
> + *
> + * This is a simple FUSE filesystem that contains two objects: a file named
> + * 'file' and a symlink to that file named 'link'.  If symlink caching is
> + * disabled (i.e. FUSE_CAP_CACHE_SYMLINKS is reset during FUSE_INIT), whenever
> + * the ->readlink() is executed to resolve 'link' a counter will be incremented.
> + *
> + * If symlink caching is enabled (i.e. FUSE_CAP_CACHE_SYMLINKS is set during
> + * FUSE_INIT), resolving a symlink will only call into user-space the first
> + * time.
> + */
> +
> +#define FUSE_USE_VERSION 31
> +
> +#include <stdio.h>
> +#include <fuse_lowlevel.h>
> +
> +#include "kselftest_harness.h"
> +
> +#include "fuse_common.h"
> +
> +#define FILENAME "file"
> +#define FILE_INO 42
> +
> +#define LINKNAME "link"
> +#define LINK_INO 43
> +
> +#define TIMEOUT	86400.0f
> +
> +struct test_state {
> +	pthread_mutex_t lock;
> +	int readlink_counter;
> +	bool cache;
> +} test_state = {
> +	.lock = PTHREAD_MUTEX_INITIALIZER,
> +};
> +
> +static void fs_init(void *userdata, struct fuse_conn_info *conn)
> +{
> +	pthread_mutex_lock(&test_state.lock);
> +	if (test_state.cache)
> +		fuse_set_feature_flag(conn, FUSE_CAP_CACHE_SYMLINKS);
> +	else
> +		fuse_unset_feature_flag(conn, FUSE_CAP_CACHE_SYMLINKS);
> +	pthread_mutex_unlock(&test_state.lock);
> +}
> +
> +static void fs_lookup(fuse_req_t req, fuse_ino_t parent, const char *name)
> +{
> +	struct fuse_entry_param e = {};
> +
> +	if (parent != FUSE_ROOT_ID ||
> +	    (strcmp(name, FILENAME) != 0 && strcmp(name, LINKNAME) != 0)) {
> +		fuse_reply_err(req, ENOENT);
> +		return;
> +	}
> +
> +	if (!strcmp(name, FILENAME)) {
> +		e.ino = FILE_INO;
> +		e.attr.st_mode = S_IFREG | 0444;
> +		e.attr.st_nlink = 2;
> +	} else if (!strcmp(name, LINKNAME)) {
> +		e.ino = LINK_INO;
> +		e.attr.st_mode = S_IFLNK | 0444;
> +		e.attr.st_nlink = 1;
> +		e.attr.st_size = strlen(FILENAME);
> +	}
> +	e.attr_timeout = TIMEOUT;
> +	e.entry_timeout = TIMEOUT;
> +
> +	fuse_reply_entry(req, &e);
> +}
> +
> +static void fs_readlink(fuse_req_t req, fuse_ino_t ino)
> +{
> +	char buf[PATH_MAX];
> +	size_t sz = strlen(FILENAME);
> +
> +	if (ino != LINK_INO) {
> +		fuse_reply_err(req, ENOENT);
> +		return;
> +	}
> +
> +	memcpy(buf, FILENAME, sz);
> +	buf[sz] = '\0';
> +	pthread_mutex_lock(&test_state.lock);
> +	test_state.readlink_counter++;
> +	pthread_mutex_unlock(&test_state.lock);
> +
> +	fuse_reply_readlink(req, buf);
> +}
> +
> +static const struct fuse_lowlevel_ops fs_ops = {
> +	.init           = fs_init,
> +	.lookup		= fs_lookup,
> +	.readlink	= fs_readlink,
> +};
> +
> +FIXTURE(symlink_cache)
> +{
> +	struct fuse_common_ctx ctx;
> +};
> +FIXTURE_VARIANT(symlink_cache)
> +{
> +	const bool cache;
> +};
> +FIXTURE_VARIANT_ADD(symlink_cache, symlinks_nocache)
> +{
> +	/* Variant with symlink cache disabled */
> +	.cache = false,
> +};
> +FIXTURE_VARIANT_ADD(symlink_cache, symlinks_cache)
> +{
> +	/* Variant with symlink cache enabled */
> +	.cache = true,
> +};
> +
> +FIXTURE_SETUP(symlink_cache)
> +{
> +	char err[MAX_ERR_MSG];
> +
> +	pthread_mutex_lock(&test_state.lock);
> +	test_state.readlink_counter = 0;
> +	test_state.cache = variant->cache;
> +	pthread_mutex_unlock(&test_state.lock);
> +
> +	if (fs_setup(&fs_ops, &self->ctx, err))
> +		SKIP(return, err);
> +}
> +
> +FIXTURE_TEARDOWN(symlink_cache)
> +{
> +	fs_teardown(&self->ctx);
> +}
> +
> +TEST_F(symlink_cache, test_symlink_cache)
> +{
> +	char pathname[PATH_MAX];
> +	char buf[PATH_MAX];
> +	ssize_t sz;
> +	int counter;
> +	int i;
> +
> +	sprintf(pathname, "%s/%s", self->ctx.mountpoint, LINKNAME);
> +	for (i = 0; i < 100; i++) {
> +		sz = readlink(pathname, buf, PATH_MAX);
> +		ASSERT_NE(sz, -1);
> +	}
> +	pthread_mutex_lock(&test_state.lock);
> +	counter = test_state.readlink_counter;
> +	pthread_mutex_unlock(&test_state.lock);
> +
> +	if (variant->cache) {
> +		ASSERT_EQ(counter, 1);
> +	} else {
> +		ASSERT_EQ(counter, 100);
> +	}
> +}
> +
> +TEST_HARNESS_MAIN
>
> base-commit: 9b1da7b4a4e197072e630c3b85d4100a399752ff
> -- 
> 2.53.0
>