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);

src/gpt-auto-generator/gpt-auto-generator.c

@@ -729,10 +729,14 @@ static int add_mounts(void) {
         int r;
 
         r = get_block_device_harder("/", &devno);
+        if (r == -EUCLEAN)
+                return btrfs_log_dev_root(LOG_ERR, r, "root file system");
         if (r < 0)
                 return log_error_errno(r, "Failed to determine block device of root file system: %m");
-        if (r == 0) {
+        if (r == 0) { /* Not backed by block device */
                 r = get_block_device_harder("/usr", &devno);
+                if (r == -EUCLEAN)
+                        return btrfs_log_dev_root(LOG_ERR, r, "/usr");
                 if (r < 0)
                         return log_error_errno(r, "Failed to determine block device of /usr file system: %m");
                 if (r == 0) {

src/partition/growfs.c

@@ -11,6 +11,7 @@
 #include <sys/vfs.h>
 
 #include "blockdev-util.h"
+#include "btrfs-util.h"
 #include "cryptsetup-util.h"
 #include "device-nodes.h"
 #include "dissect-image.h"
@@ -96,6 +97,8 @@ static int maybe_resize_underlying_device(const char *mountpath, dev_t main_devn
         if (r < 0)
                 return log_error_errno(r, "Failed to determine underlying block device of \"%s\": %m",
                                        mountpath);
+        if (devno == 0)
+                return log_error_errno(SYNTHETIC_ERRNO(ENODEV), "File system \"%s\" not backed by block device.", arg_target);
 
         log_debug("Underlying device %d:%d, main dev %d:%d, %s",
                   major(devno), minor(devno),
@@ -212,8 +215,12 @@ static int run(int argc, char *argv[]) {
                 return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "\"%s\" is not a mount point: %m", arg_target);
 
         r = get_block_device(arg_target, &devno);
+        if (r == -EUCLEAN)
+                return btrfs_log_dev_root(LOG_ERR, r, arg_target);
         if (r < 0)
                 return log_error_errno(r, "Failed to determine block device of \"%s\": %m", arg_target);
+        if (devno == 0)
+                return log_error_errno(SYNTHETIC_ERRNO(ENODEV), "File system \"%s\" not backed by block device.", arg_target);
 
         r = maybe_resize_underlying_device(arg_target, devno);
         if (r < 0)

src/partition/repart.c

@@ -3369,6 +3369,8 @@ static int context_open_copy_block_paths(Context *context) {
                                 /* Special support for btrfs */
 
                                 r = btrfs_get_block_device_fd(source_fd, &devt);
+                                if (r == -EUCLEAN)
+                                        return btrfs_log_dev_root(LOG_ERR, r, p->copy_blocks_path);
                                 if (r < 0)
                                         return log_error_errno(r, "Unable to determine backing block device of '%s': %m", p->copy_blocks_path);
 
@@ -3833,6 +3835,8 @@ static int find_root(char **ret, int *ret_fd) {
                 }
 
                 r = acquire_root_devno(arg_node, O_RDONLY|O_CLOEXEC, ret, ret_fd);
+                if (r == -EUCLEAN)
+                        return btrfs_log_dev_root(LOG_ERR, r, arg_node);
                 if (r < 0)
                         return log_error_errno(r, "Failed to open file or determine backing device of %s: %m", arg_node);
 
@@ -3860,6 +3864,8 @@ static int find_root(char **ret, int *ret_fd) {
 
                 r = acquire_root_devno(p, O_RDONLY|O_DIRECTORY|O_CLOEXEC, ret, ret_fd);
                 if (r < 0) {
+                        if (r == -EUCLEAN)
+                                return btrfs_log_dev_root(LOG_ERR, r, p);
                         if (r != -ENODEV)
                                 return log_error_errno(r, "Failed to determine backing device of %s: %m", p);
                 } else

src/shared/sleep-config.c

@@ -403,6 +403,8 @@ int find_hibernate_location(HibernateLocation **ret_hibernate_location) {
                 r = swap_device_to_device_id(swap, &swap_device);
                 if (r < 0)
                         return log_debug_errno(r, "%s: failed to query device number: %m", swap->device);
+                if (swap_device == 0)
+                        return log_debug_errno(SYNTHETIC_ERRNO(ENODEV), "%s: not backed by block device.", swap->device);
 
                 hibernate_location = hibernate_location_free(hibernate_location);
                 hibernate_location = new(HibernateLocation, 1);

src/volatile-root/volatile-root.c

@@ -175,7 +175,7 @@ static int run(int argc, char *argv[]) {
         r = get_block_device_harder(path, &devt);
         if (r < 0)
                 return log_error_errno(r, "Failed to determine device major/minor of %s: %m", path);
-        else if (r > 0) {
+        else if (r > 0) { /* backed by block device */
                 _cleanup_free_ char *dn = NULL;
 
                 r = device_path_make_major_minor(S_IFBLK, devt, &dn);