idmapped-mounts: add fs_allow_idmap() helper

Move the check whether the underlying filesystem supports idmapped
mounts into a separate helper. We will use it in the following patch to
make it possible to always run all tests that don't require idmapped
mounts.

Link: https://lore.kernel.org/r/20220113132421.865002-1-brauner@kernel.org
Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Eryu Guan <guaneryu@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: fstests@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

diff --git a/src/idmapped-mounts/idmapped-mounts.c b/src/idmapped-mounts/idmapped-mounts.c
index a5c0a983e6e012ef41da14c5d60edc38d81b8388..fc305606e62bdf1200661ba1198dd7ff8a330b96 100644 (file)
--- a/src/idmapped-mounts/idmapped-mounts.c
+++ b/src/idmapped-mounts/idmapped-mounts.c
@@ -13955,6 +13955,35 @@ static bool run_test(struct t_idmapped_mounts suite[], size_t suite_size)
        return true;
 }
 
+static bool fs_allow_idmap(void)
+{
+       int ret;
+       int open_tree_fd = -EBADF;
+       struct mount_attr attr = {
+               .attr_set       = MOUNT_ATTR_IDMAP,
+               .userns_fd      = -EBADF,
+       };
+
+       /* Changing mount properties on a detached mount. */
+       attr.userns_fd = get_userns_fd(0, 1000, 1);
+       if (attr.userns_fd < 0)
+               return false;
+
+       open_tree_fd = sys_open_tree(t_mnt_fd, "",
+                                    AT_EMPTY_PATH | AT_NO_AUTOMOUNT |
+                                    AT_SYMLINK_NOFOLLOW | OPEN_TREE_CLOEXEC |
+                                    OPEN_TREE_CLONE);
+       if (open_tree_fd < 0)
+               ret = -1;
+       else
+               ret = sys_mount_setattr(open_tree_fd, "", AT_EMPTY_PATH, &attr,
+                                       sizeof(attr));
+       close(open_tree_fd);
+       close(attr.userns_fd);
+
+       return ret == 0;
+}
+
 int main(int argc, char *argv[])
 {
        int fret, ret;
@@ -14035,34 +14064,8 @@ int main(int argc, char *argv[])
         * idmapped mounts.
         */
        if (supported) {
-               int open_tree_fd = -EBADF;
-               struct mount_attr attr = {
-                       .attr_set       = MOUNT_ATTR_IDMAP,
-                       .userns_fd      = -EBADF,
-               };
-
-               /* Changing mount properties on a detached mount. */
-               attr.userns_fd  = get_userns_fd(0, 1000, 1);
-               if (attr.userns_fd < 0)
+               if (!fs_allow_idmap())
                        exit(EXIT_FAILURE);
-
-               open_tree_fd = sys_open_tree(t_mnt_fd, "",
-                                            AT_EMPTY_PATH |
-                                            AT_NO_AUTOMOUNT |
-                                            AT_SYMLINK_NOFOLLOW |
-                                            OPEN_TREE_CLOEXEC |
-                                            OPEN_TREE_CLONE);
-               if (open_tree_fd < 0)
-                       ret = -1;
-               else
-                       ret = sys_mount_setattr(open_tree_fd, "", AT_EMPTY_PATH, &attr, sizeof(attr));
-
-               close(open_tree_fd);
-               close(attr.userns_fd);
-
-               if (ret)
-                       exit(EXIT_FAILURE);
-
                exit(EXIT_SUCCESS);
        }