fstab-generator: fix spurious quota warning for xfs

Filesystems like xfs, btrfs, gfs2 and ocfs2 handle quotas internally
and do not need external quotacheck/quotaon services. When usrquota or
grpquota mount options are used in fstab for these filesystems,
generator_hook_up_quotacheck() falls through to the !fstype_needs_quota()
branch and emits a misleading warning that quotas are "not supported"
when they actually work fine — the kernel handles them internally.

Add fstype_has_internal_quota() to return early with a debug message,
and adopt a tri-state return convention so the caller skips quotaon
when quotacheck was not needed.

The buggy code path was introduced in #24824 and #24880.

Co-developed-by: Claude Opus 4.6 <noreply@anthropic.com>

src/basic/mountpoint-util.c

@@ -385,6 +385,17 @@ bool fstype_needs_quota(const char *fstype) {
                           "f2fs");
 }
 
+bool fstype_has_internal_quota(const char *fstype) {
+        /* These filesystems have built-in quota support and do not need
+         * external quotacheck/quotaon services - see the "nothing needed"
+         * entries in fstype_needs_quota() above. */
+        return STR_IN_SET(fstype,
+                          "xfs",
+                          "gfs2",
+                          "ocfs2",
+                          "btrfs");
+}
+
 bool fstype_is_api_vfs(const char *fstype) {
         assert(fstype);
 

src/basic/mountpoint-util.h

@@ -61,6 +61,7 @@ static inline int path_is_mount_point(const char *path) {
 
 bool fstype_is_network(const char *fstype);
 bool fstype_needs_quota(const char *fstype);
+bool fstype_has_internal_quota(const char *fstype);
 bool fstype_is_api_vfs(const char *fstype);
 bool fstype_is_blockdev_backed(const char *fstype);
 bool fstype_is_ro(const char *fsype);