Re: [RFC PATCH v1 5/5] selftests/filesystems: add fuse ACLs caching test

[Luis Henriques]

Amir Goldstein <amir73il@xxxxxxxxx> writes:

> On Wed, Jul 8, 2026 at 3:11 PM Luis Henriques <luis@xxxxxxxxxx> wrote:
>>
>> This patch adds a simple test that allows to verify that ACLs caching is
>> working as expected.  I.e. it verifies that, if FUSE_POSIX_ACL flag is set,
>> user-space is only called once when accessing an inode ACL and that
>> subsequent accesses are cached in the kernel.
>>
>> Signed-off-by: Luis Henriques <luis@xxxxxxxxxx>
>> ---
>>  .../selftests/filesystems/fuse/.gitignore     |   2 +
>>  .../selftests/filesystems/fuse/Makefile       |  13 +-
>>  .../selftests/filesystems/fuse/acl_fs.c       | 216 ++++++++++++++++++
>>  .../selftests/filesystems/fuse/acl_test.sh    |  66 ++++++
>>  .../selftests/filesystems/fuse/setgetacl.c    |  62 +++++
>>  5 files changed, 357 insertions(+), 2 deletions(-)
>>  create mode 100644 tools/testing/selftests/filesystems/fuse/acl_fs.c
>>  create mode 100755 tools/testing/selftests/filesystems/fuse/acl_test.sh
>>  create mode 100644 tools/testing/selftests/filesystems/fuse/setgetacl.c
>>
>> diff --git a/tools/testing/selftests/filesystems/fuse/.gitignore b/tools/testing/selftests/filesystems/fuse/.gitignore
>> index cfdc5ca3ded4..1733ebb9d7fd 100644
>> --- a/tools/testing/selftests/filesystems/fuse/.gitignore
>> +++ b/tools/testing/selftests/filesystems/fuse/.gitignore
>> @@ -2,3 +2,5 @@
>>  fuse_mnt
>>  fusectl_test
>>  symlink_fs
>> +acl_fs
>> +setgetacl
>> diff --git a/tools/testing/selftests/filesystems/fuse/Makefile b/tools/testing/selftests/filesystems/fuse/Makefile
>> index 342da0878006..3bbf9d837e9a 100644
>> --- a/tools/testing/selftests/filesystems/fuse/Makefile
>> +++ b/tools/testing/selftests/filesystems/fuse/Makefile
>> @@ -3,8 +3,8 @@
>>  CFLAGS += -Wall -O2 -g $(KHDR_INCLUDES)
>>
>>  TEST_GEN_PROGS := fusectl_test
>> -TEST_PROGS := symlink_test.sh
>> -TEST_GEN_FILES := fuse_mnt symlink_fs
>> +TEST_PROGS := symlink_test.sh acl_test.sh
>> +TEST_GEN_FILES := fuse_mnt symlink_fs acl_fs setgetacl
>>
>>  include ../../lib.mk
>>
>> @@ -18,8 +18,17 @@ ifeq ($(VAR_LDLIBS),)
>>  VAR_LDLIBS := -lfuse3 -pthread
>>  endif
>>
>> +ACL_CFLAGS := $(shell pkg-config libacl --cflags 2>/dev/null)
>> +ACL_LDLIBS := $(shell pkg-config libacl --libs 2>/dev/null)
>> +
>>  $(OUTPUT)/fuse_mnt: CFLAGS += $(VAR_CFLAGS)
>>  $(OUTPUT)/fuse_mnt: LDLIBS += $(VAR_LDLIBS)
>>
>>  $(OUTPUT)/symlink_fs: CFLAGS += $(VAR_CFLAGS)
>>  $(OUTPUT)/symlink_fs: LDLIBS += $(VAR_LDLIBS)
>> +
>> +$(OUTPUT)/acl_fs: CFLAGS += $(VAR_CFLAGS)
>> +$(OUTPUT)/acl_fs: LDLIBS += $(VAR_LDLIBS)
>> +
>> +$(OUTPUT)/setgetacl: CFLAGS += $(ACL_CFLAGS)
>> +$(OUTPUT)/setgetacl: LDLIBS += $(ACL_LDLIBS)
>> diff --git a/tools/testing/selftests/filesystems/fuse/acl_fs.c b/tools/testing/selftests/filesystems/fuse/acl_fs.c
>> new file mode 100644
>> index 000000000000..4b5e0073ab4f
>> --- /dev/null
>> +++ b/tools/testing/selftests/filesystems/fuse/acl_fs.c
>> @@ -0,0 +1,216 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +
>> +/*
>> + * Simple filesystem to test FUSE ACLs cache
>> + *
>> + * This is a simple FUSE filesystem that contains a single object (a file named
>> + * 'file') and which allows to set the 'system.posix_acl_access' ACL on that
>> + * object.  Whenever this ACL is read from the FUSE filesystem, a counter is
>> + * incremented.  And value for this counter can be obtained from reading from
>> + * this file.
>> + *
>> + * When ACLs are being cached (the '--cache' argument was used to mount this
>> + * filesystem), this counter will only be incremented the first time the ACL is
>> + * read, as the kernel won't be calling into user-space again until that cache
>> + * is invalidated.
>> + */
>> +#define FUSE_USE_VERSION FUSE_MAKE_VERSION(3, 12)
>> +
>> +#include <fuse_lowlevel.h>
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <string.h>
>> +#include <errno.h>
>> +#include <fcntl.h>
>> +#include <time.h>
>> +#include <sys/stat.h>
>> +#include <sys/param.h>
>> +#include <sys/xattr.h>
>> +
>> +#define FILE   "file"
>> +#define TIMEOUT        86400.0f
>> +
>> +static struct options {
>> +       int cache_acls;
>> +} options;
>> +
>> +static const struct fuse_opt option_spec[] = {
>> +       { "--cache", offsetof(struct options, cache_acls), 1 },
>> +       FUSE_OPT_END
>> +};
>> +
>> +static int getxattr_counter = 0;
>> +
>> +static void acl_init(void *userdata, struct fuse_conn_info *conn)
>> +{
>> +       if (options.cache_acls)
>> +               fuse_set_feature_flag(conn, FUSE_CAP_POSIX_ACL);
>> +       else
>> +               fuse_unset_feature_flag(conn, FUSE_CAP_POSIX_ACL);
>> +}
>> +
>> +static int acl_stat(fuse_ino_t ino, struct stat *stbuf)
>> +{
>> +       char data[64];
>> +
>> +       stbuf->st_ino = ino;
>> +       switch (ino) {
>> +       case 1:
>> +               stbuf->st_mode = S_IFDIR | 0755;
>> +               stbuf->st_nlink = 2;
>> +               break;
>> +       case 42:
>> +               stbuf->st_mode = S_IFREG | 0444;
>> +               stbuf->st_nlink = 1;
>> +               stbuf->st_size = sprintf(data, "%d\n", getxattr_counter);
>> +               break;
>> +       default:
>> +               return -1;
>> +       }
>> +
>> +       stbuf->st_uid = getuid();
>> +       stbuf->st_gid = getgid();
>> +       stbuf->st_atime = stbuf->st_mtime = stbuf->st_ctime = time(NULL);
>> +
>> +       return 0;
>> +}
>> +
>> +static void acl_lookup(fuse_req_t req, fuse_ino_t parent, const char *name)
>> +{
>> +       struct fuse_entry_param e;
>> +
>> +       memset(&e, 0, sizeof(e));
>> +
>> +       if (parent != 1 || strcmp(name, FILE) != 0)
>> +               fuse_reply_err(req, ENOENT);
>> +       else {
>> +               e.ino = 42;
>> +               e.attr_timeout = TIMEOUT;
>> +               e.entry_timeout = TIMEOUT;
>> +               acl_stat(e.ino, &e.attr);
>> +               fuse_reply_entry(req, &e);
>> +       }
>> +}
>> +
>> +static void acl_getattr(fuse_req_t req, fuse_ino_t ino,
>> +                       struct fuse_file_info *fi)
>> +{
>> +       struct stat attr;
>> +
>> +       memset(&attr, 0, sizeof(struct stat));
>> +       if (acl_stat(ino, &attr) == -1)
>> +               fuse_reply_err(req, ENOENT);
>> +       else
>> +               fuse_reply_attr(req, &attr, TIMEOUT);
>> +}
>> +
>> +static void acl_read(fuse_req_t req, fuse_ino_t ino, size_t size,
>> +                    off_t off, struct fuse_file_info *fi)
>> +{
>> +       char data[64];
>> +       int len;
>> +
>> +       len = sprintf(data, "%d\n", getxattr_counter);
>> +       if (off < len)
>> +               fuse_reply_buf(req, data + off, MIN(len - off, size));
>> +       else
>> +               fuse_reply_buf(req, NULL, 0);
>> +}
>> +
>> +char *xattr_value = NULL;
>> +size_t xattr_value_sz = 0;
>> +
>> +static void acl_setxattr(fuse_req_t req, fuse_ino_t ino, const char *name,
>> +                        const char *value, size_t size, int flags)
>> +{
>> +       int ret = 0;
>> +
>> +       if (ino != 42)
>> +               ret = ENOENT;
>> +       else if (!strcmp(name, "system.posix_acl_access")) {
>> +               if (xattr_value)
>> +                       free(xattr_value);
>> +               xattr_value = malloc(size);
>> +               memcpy(xattr_value, value, size);
>> +               xattr_value_sz = size;
>> +       } else
>> +               ret = ENOTSUP;
>> +
>> +       fuse_reply_err(req, ret);
>> +}
>> +
>> +static void acl_getxattr(fuse_req_t req, fuse_ino_t ino, const char *name,
>> +                        size_t size)
>> +{
>> +       if (ino != 42)
>> +               fuse_reply_err(req, ENOENT);
>> +       else if (!xattr_value || strcmp(name, "system.posix_acl_access"))
>> +               fuse_reply_err(req, ENODATA);
>> +       else if (size) {
>> +               fuse_reply_buf(req, xattr_value, xattr_value_sz);
>> +               getxattr_counter++;
>> +       } else
>> +               fuse_reply_xattr(req, xattr_value_sz);
>> +}
>> +
>> +static const struct fuse_lowlevel_ops acl_op = {
>> +       .init           = acl_init,
>> +       .lookup         = acl_lookup,
>> +       .getattr        = acl_getattr,
>> +       .getxattr       = acl_getxattr,
>> +       .setxattr       = acl_setxattr,
>> +       .read           = acl_read,
>> +};
>> +
>> +int main(int argc, char *argv[])
>> +{
>> +       struct fuse_session *se;
>> +       struct fuse_loop_config *config;
>> +       struct fuse_args args = FUSE_ARGS_INIT(argc, argv);
>> +       struct fuse_cmdline_opts opts;
>> +       int ret = -1;
>> +
>> +       options.cache_acls = 0;
>> +
>> +       if (fuse_parse_cmdline(&args, &opts) != 0)
>> +               return ret;
>> +
>> +       if (opts.mountpoint == NULL) {
>> +               printf("usage: %s [options] <mountpoint>\n", argv[0]);
>> +               goto out_args;
>> +       }
>> +
>> +       if (fuse_opt_parse(&args, &options, option_spec, NULL) == -1)
>> +               goto out_args;
>> +
>> +       se = fuse_session_new(&args, &acl_op, sizeof(acl_op), NULL);
>> +       if (!se)
>> +               goto out_args;
>> +       if (fuse_set_signal_handlers(se))
>> +               goto out_session;
>> +       if (fuse_session_mount(se, opts.mountpoint))
>> +               goto out_signal;
>> +
>> +       fuse_daemonize(opts.foreground);
>> +       if (opts.singlethread) {
>> +               ret = fuse_session_loop(se);
>> +       } else {
>> +               config = fuse_loop_cfg_create();
>> +               fuse_loop_cfg_set_clone_fd(config, opts.clone_fd);
>> +               fuse_loop_cfg_set_max_threads(config, opts.max_threads);
>> +               ret = fuse_session_loop_mt(se, config);
>> +               fuse_loop_cfg_destroy(config);
>> +               config = NULL;
>> +       }
>> +       fuse_session_unmount(se);
>> +
>> +out_signal:
>> +       fuse_remove_signal_handlers(se);
>> +out_session:
>> +       fuse_session_destroy(se);
>> +out_args:
>> +       free(opts.mountpoint);
>> +       fuse_opt_free_args(&args);
>> +
>> +       return ret;
>> +}
>> diff --git a/tools/testing/selftests/filesystems/fuse/acl_test.sh b/tools/testing/selftests/filesystems/fuse/acl_test.sh
>> new file mode 100755
>> index 000000000000..9070c51c6784
>> --- /dev/null
>> +++ b/tools/testing/selftests/filesystems/fuse/acl_test.sh
>> @@ -0,0 +1,66 @@
>> +#!/bin/sh
>> +# SPDX-License-Identifier: GPL-2.0
>> +
>> +exit_cleanup()
>> +{
>> +       fusermount -u ./mnt
>> +       rmdir ./mnt
>> +}
>> +
>> +assert_value ()
>> +{
>> +       if [ $1 -ne $2 ]; then
>> +               echo "FAILED"
>> +               echo $3
>> +               exit 1
>> +       fi
>> +}
>> +
>> +set -e
>> +
>> +trap exit_cleanup EXIT
>> +
>> +mkdir -p mnt
>> +
>> +#sudo su -
>> +#cd /home/miguel/kernel/linux/tools/testing/selftests/filesystems/fuse
>> +#dmesg -c > /dev/null
>> +#tmux -S ./bla -f a
>> +#./acl_fs -d --cache ./mnt
>> +#setfacl -m u:daemon:r mnt/file
>> +#getfacl mnt/file
>> +
>> +./acl_fs ./mnt
>> +
>> +echo -n "Testing ACLs without cache: "
>> +
>> +# set ACL
>> +./setgetacl ACCESS u::rw-,g::rw-,o::rw-,u:nobody:r--,m::rw- mnt/file
>> +
>> +# When symlink caching is disabled every access to a symlink is expected to
>> +# result in a call to user-space
>> +for i in $(seq 1 10); do
>> +       ./setgetacl ACCESS mnt/file > /dev/null
>> +done
>> +
>> +res=$(cat ./mnt/file)
>> +assert_value $res $i "Got $res, expected $i"
>> +echo "PASSED"
>> +
>> +fusermount -u ./mnt
>> +
>> +./acl_fs --cache ./mnt
>> +
>> +echo -n "Testing ACLs with cache: "
>> +
>> +# set ACL
>> +./setgetacl ACCESS u::rw-,g::rw-,o::rw-,u:nobody:r--,m::rw- mnt/file
>> +
>> +# With caching enabled, there will be a single call into user-space
>> +for i in $(seq 1 10); do
>> +       ./setgetacl ACCESS mnt/file > /dev/null
>> +done
>> +res=$(cat ./mnt/file)
>> +assert_value $res 1 "Got $res, expected 1"
>> +
>> +echo "PASSED"
>> diff --git a/tools/testing/selftests/filesystems/fuse/setgetacl.c b/tools/testing/selftests/filesystems/fuse/setgetacl.c
>> new file mode 100644
>> index 000000000000..035e7daa1c5d
>> --- /dev/null
>> +++ b/tools/testing/selftests/filesystems/fuse/setgetacl.c
>> @@ -0,0 +1,62 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +
>> +/* Simple ACL set/get wrapper */
>> +
>> +#include <stdio.h>
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <string.h>
>> +#include <sys/types.h>
>> +#include <sys/acl.h>
>> +
>> +int main(int argc, char *argv[])
>> +{
>> +       acl_t acl;
>> +       acl_type_t type;
>> +       char *buf;
>> +
>> +       if ((argc != 3) && (argc != 4)) {
>> +               fprintf(stderr, "Usage: %s <acl type> [<value>] <file>\n",
>> +                       argv[0]);
>> +               fprintf(stderr, "where <acl type> is ACCESS or DEFAULT\n");
>> +               return 1;
>> +       }
>> +
>> +       if (!strcmp(argv[1], "ACCESS"))
>> +               type = ACL_TYPE_ACCESS;
>> +       else if (!strcmp(argv[1], "DEFAULT"))
>> +               type = ACL_TYPE_DEFAULT;
>> +       else {
>> +               fprintf(stderr, "Invalid ACL type\n");
>> +               return 1;
>> +       }
>> +
>> +       if (argc == 3) {
>> +               /* Get ACL */
>> +               acl = acl_get_file(argv[2], type);
>> +               if (acl == NULL) {
>> +                       perror("acl_get_file");
>> +                       return 1;
>> +               }
>> +               buf = acl_to_text(acl, NULL);
>> +               if (buf == NULL)
>> +                       perror("acl_from_text");
>> +               else {
>> +                       fprintf(stdout, "%s\n", buf);
>> +                       acl_free(buf);
>> +               }
>> +       } else {
>> +               /* Set ACL */
>> +               acl = acl_from_text(argv[2]);
>> +               if (acl == NULL) {
>> +                       perror("acl_from_text");
>> +                       return 1;
>> +               }
>> +               if (acl_set_file(argv[3], type, acl) != 0)
>> +                       perror("acl_set_file");
>> +       }
>> +
>> +       acl_free(acl);
>> +
>> +       return 0;
>> +}
>>
>
> I think this test is already covered by
> https://lore.kernel.org/linux-fsdevel/20260713220932.413004-3-amir73il@xxxxxxxxx/
>
> If there is any missing coverage, it could be added to my test,
> assuming that my test (which tests a regression) will be merged first.

Sure, that makes sense.  I will make sure that any addition ACL testing is
added to your selftest.  To be honest, I saw your fix+selftest only
*after* sending this RFC :-)

Thanks a lot for your feedback, Amir.

Cheers,
-- 
Luís