chattr-util/acl-util: add helpers that tells us if an inode type can do chattr/acl (#39003)

Split out of #38728 but I think this makes things more readable in
general and makes sense on its own.

src/basic/chattr-util.c

@@ -41,7 +41,7 @@ int chattr_full(
          * drivers, where the ioctl might have different effects. Notably, DRM is using the same
          * ioctl() number. */
 
-        if (!S_ISDIR(st.st_mode) && !S_ISREG(st.st_mode))
+        if (!inode_type_can_chattr(st.st_mode))
                 return -ENOTTY;
 
         if (mask == 0 && !ret_previous && !ret_final)
@@ -140,7 +140,7 @@ int read_attr_fd(int fd, unsigned *ret) {
         if (fstat(fd, &st) < 0)
                 return -errno;
 
-        if (!S_ISDIR(st.st_mode) && !S_ISREG(st.st_mode))
+        if (!inode_type_can_chattr(st.st_mode))
                 return -ENOTTY;
 
         _cleanup_close_ int fd_close = -EBADF;
@@ -248,3 +248,7 @@ int set_proj_id_recursive(int fd, uint32_t proj_id) {
                         set_proj_id_cb,
                         UINT32_TO_PTR(proj_id));
 }
+
+bool inode_type_can_chattr(mode_t mode) {
+        return IN_SET(mode & S_IFMT, S_IFREG, S_IFDIR);
+}

src/basic/chattr-util.h

@@ -63,3 +63,5 @@ int set_proj_id_recursive(int fd, uint32_t proj_id);
 static inline int chattr_secret(int fd, ChattrApplyFlags flags) {
         return chattr_full(fd, NULL, CHATTR_SECRET_FLAGS, CHATTR_SECRET_FLAGS, NULL, NULL, flags|CHATTR_FALLBACK_BITWISE);
 }
+
+bool inode_type_can_chattr(mode_t mode);

src/shared/acl-util.c

@@ -648,3 +648,7 @@ int fd_acl_make_writable_fallback(int fd) {
 
         return 1;
 }
+
+int inode_type_can_acl(mode_t mode) {
+        return IN_SET(mode & S_IFMT, S_IFSOCK, S_IFREG, S_IFBLK, S_IFCHR, S_IFDIR, S_IFIFO);
+}

src/shared/acl-util.h

@@ -53,3 +53,5 @@ static inline int fd_acl_make_writable(int fd) {
 }
 
 #endif
+
+int inode_type_can_acl(mode_t mode);

src/shared/shift-uid.c

@@ -161,7 +161,7 @@ static int patch_acls(int fd, const char *name, const struct stat *st, uid_t shi
         assert(st);
 
         /* ACLs are not supported on symlinks, there's no point in trying */
-        if (S_ISLNK(st->st_mode))
+        if (!inode_type_can_acl(st->st_mode))
                 return 0;
 
         r = get_acl(fd, name, ACL_TYPE_ACCESS, &acl);

src/tmpfiles/tmpfiles.c

@@ -1459,8 +1459,8 @@ static int fd_set_acls(
                                        "Refusing to set ACLs on hardlinked file %s while the fs.protected_hardlinks sysctl is turned off.",
                                        path);
 
-        if (S_ISLNK(st->st_mode)) {
-                log_debug("Skipping ACL fix for symlink %s.", path);
+        if (!inode_type_can_acl(st->st_mode)) {
+                log_debug("Skipping ACL fix for '%s' (inode type does not support ACLs).", path);
                 return 0;
         }