Merge pull request #16973 from poettering/btrfs-dev-root

print friendly error message if btrfs tells us /dev/root was backing block device of root fs

src/basic/btrfs-util.c

@@ -315,6 +315,15 @@ int btrfs_get_block_device_fd(int fd, dev_t *dev) {
                         return -errno;
                 }
 
+                /* For the root fs — when no initrd is involved — btrfs returns /dev/root on any kernels from
+                 * the past few years. That sucks, as we have no API to determine the actual root then. let's
+                 * return an recognizable error for this case, so that the caller can maybe print a nice
+                 * message about this.
+                 *
+                 * https://bugzilla.kernel.org/show_bug.cgi?id=89721 */
+                if (path_equal((char*) di.path, "/dev/root"))
+                        return -EUCLEAN;
+
                 if (stat((char*) di.path, &st) < 0)
                         return -errno;
 

src/basic/btrfs-util.h

@@ -121,3 +121,9 @@ int btrfs_qgroup_find_parents(int fd, uint64_t qgroupid, uint64_t **ret);
 
 int btrfs_qgroup_get_quota_fd(int fd, uint64_t qgroupid, BtrfsQuotaInfo *quota);
 int btrfs_qgroup_get_quota(const char *path, uint64_t qgroupid, BtrfsQuotaInfo *quota);
+
+static inline int btrfs_log_dev_root(int level, int ret, const char *p) {
+        return log_full_errno(level, ret,
+                              "File system behind %s is reported by btrfs to be backed by pseudo-device /dev/root, which is not a valid userspace accessible device node. "
+                              "Cannot determine correct backing block device.", p);
+}

src/basic/quota-util.c

@@ -34,7 +34,7 @@ int quotactl_path(int cmd, const char *path, int id, void *addr) {
         r = get_block_device(path, &devno);
         if (r < 0)
                 return r;
-        if (devno == 0)
+        if (devno == 0) /* Doesn't have a block device */
                 return -ENODEV;
 
         return quotactl_devno(cmd, devno, id, addr);