From: Karel Zak <kzak@redhat.com>
Date: Thu, 25 Jun 2026 10:32:31 +0000 (+0200)
Subject: libmount: add mnt_fs_fetch_ids() and populate uniq_id for utab
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=1cb24d37de96f32596164ce738713c0c04086044;p=thirdparty%2Futil-linux.git

libmount: add mnt_fs_fetch_ids() and populate uniq_id for utab

Add mnt_fs_fetch_ids() helper that fetches mount IDs from the kernel
via statx(). It prefers STATX_MNT_ID_UNIQUE and falls back to the old
STATX_MNT_ID on older kernels. Accepts an optional fd argument; when
fd < 0 it falls back to path-based lookup via fs->target.

Use it in hook_create_mount() (new mount API) with fd_tree for robust
fd-based ID, and in hook_mount() (legacy mount(2)) after
reopen_target_fd with fd_target when available.

This ensures utab entries contain UNIQID, which is needed for reliable
utab merging with listmount-based tables.

Signed-off-by: Karel Zak <kzak@redhat.com>
---

diff --git a/libmount/src/fs.c b/libmount/src/fs.c
index a0d18a4f9..8da98cc84 100644
--- a/libmount/src/fs.c
+++ b/libmount/src/fs.c
@@ -1533,6 +1533,45 @@ int mnt_fs_set_uniq_id(struct libmnt_fs *fs, uint64_t id)
 	return 0;
 }
 
+/*
+ * Fetch mount IDs from kernel via statx(). Prefers unique ID, falls back
+ * to old ID on old kernels. Uses @fd (AT_EMPTY_PATH) if >= 0, otherwise
+ * uses fs->target path.
+ *
+ * Returns: 0 on success, <0 on error.
+ */
+int mnt_fs_fetch_ids(struct libmnt_fs *fs, int fd)
+{
+	uint64_t uniq_id = 0;
+	int id = 0, rc;
+
+	if (!fs)
+		return -EINVAL;
+	if (fd < 0 && !mnt_fs_get_target(fs))
+		return -EINVAL;
+
+	if (fd >= 0)
+		rc = mnt_id_from_fd(fd, &uniq_id, NULL);
+	else
+		rc = mnt_id_from_path(mnt_fs_get_target(fs), &uniq_id, NULL);
+
+	if (rc == 0 && uniq_id > 0) {
+		fs->uniq_id = uniq_id;
+		return 0;
+	}
+
+	/* fallback to old mount ID */
+	if (fd >= 0)
+		rc = mnt_id_from_fd(fd, NULL, &id);
+	else
+		rc = mnt_id_from_path(mnt_fs_get_target(fs), NULL, &id);
+
+	if (rc == 0)
+		fs->id = id;
+
+	return rc;
+}
+
 /**
  * mnt_fs_get_parent_id:
  * @fs: /proc/self/mountinfo entry
diff --git a/libmount/src/hook_mount.c b/libmount/src/hook_mount.c
index 1dab62c68..acd0df027 100644
--- a/libmount/src/hook_mount.c
+++ b/libmount/src/hook_mount.c
@@ -323,24 +323,22 @@ static int hook_create_mount(struct libmnt_context *cxt,
 		/* cleanup after fail (libmount may only try the FS type) */
 		close_sysapi_fds(api);
 
-#if defined(HAVE_STATX) && defined(HAVE_STRUCT_STATX) && defined(HAVE_STRUCT_STATX_STX_MNT_ID)
 	if (!rc && cxt->fs) {
-		struct statx st;
-
-		rc = statx(api->fd_tree, "", AT_EMPTY_PATH, STATX_MNT_ID, &st);
-		if (rc == 0) {
-			cxt->fs->id = (int) st.stx_mnt_id;
-			if (cxt->update) {
-				struct libmnt_fs *fs = mnt_update_get_fs(cxt->update);
-				if (fs)
-					fs->id = cxt->fs->id;
+		mnt_fs_fetch_ids(cxt->fs, api->fd_tree);
+
+		if ((cxt->fs->id || cxt->fs->uniq_id) && cxt->update) {
+			struct libmnt_fs *fs = mnt_update_get_fs(cxt->update);
+			if (fs) {
+				fs->id = cxt->fs->id;
+				fs->uniq_id = cxt->fs->uniq_id;
 			}
 		}
 	}
-#endif
 
 done:
-	DBG_OBJ(HOOK, hs, ul_debug("create FS done [rc=%d, id=%d]", rc, cxt->fs ? cxt->fs->id : -1));
+	DBG_OBJ(HOOK, hs, ul_debug("create FS done [rc=%d, id=%d, uniq=%" PRIu64 "]",
+				rc, cxt->fs ? cxt->fs->id : -1,
+				cxt->fs ? cxt->fs->uniq_id : (uint64_t) 0));
 	return rc;
 }
 
diff --git a/libmount/src/hook_mount_legacy.c b/libmount/src/hook_mount_legacy.c
index 86b1c9f06..0327db4c2 100644
--- a/libmount/src/hook_mount_legacy.c
+++ b/libmount/src/hook_mount_legacy.c
@@ -251,10 +251,25 @@ static int hook_mount(struct libmnt_context *cxt,
 	else
 		mnt_fs_mark_attached(cxt->fs);
 
+	cxt->syscall_status = 0;
+
 	/* re-open to point to the mounted filesystem root */
 	rc = mnt_context_reopen_target_fd(cxt);
 
-	cxt->syscall_status = 0;
+	/* Fetch mount IDs for utab. Note that IDs are not 100% robust
+	 * with mount(2) -- another process could overmount the target
+	 * between mount(2) and our statx() call. */
+	if (rc == 0 && cxt->fs && cxt->update && mnt_update_is_ready(cxt->update)) {
+		mnt_fs_fetch_ids(cxt->fs, cxt->fd_target);
+		if (cxt->fs->id || cxt->fs->uniq_id) {
+			struct libmnt_fs *fs = mnt_update_get_fs(cxt->update);
+			if (fs) {
+				fs->id = cxt->fs->id;
+				fs->uniq_id = cxt->fs->uniq_id;
+			}
+		}
+	}
+
 	return rc;
 }
 
diff --git a/libmount/src/mountP.h b/libmount/src/mountP.h
index 01af14f3f..3f5a93d94 100644
--- a/libmount/src/mountP.h
+++ b/libmount/src/mountP.h
@@ -140,6 +140,7 @@ extern int mnt_tmptgt_unshare(int *old_ns_fd);
 extern int mnt_tmptgt_cleanup(int old_ns_fd);
 
 extern int mnt_id_from_fd(int fd, uint64_t *uniq_id, int *id);
+extern int mnt_fs_fetch_ids(struct libmnt_fs *fs, int fd);
 
 /* tab.c */
 extern int is_mountinfo(struct libmnt_table *tb);