mkfs-util: Add root support for ext and btrfs

For these filesysrems, it's useful to provide the filesystem upfront
so that we don't have to mount it later which requires root privileges.

src/shared/mkfs-util.c

@@ -33,6 +33,10 @@ int mkfs_exists(const char *fstype) {
         return true;
 }
 
+int mkfs_supports_root_option(const char *fstype) {
+        return fstype_is_ro(fstype) || STR_IN_SET(fstype, "ext2", "ext3", "ext4", "btrfs");
+}
+
 static int mangle_linux_fs_label(const char *s, size_t max_len, char **ret) {
         /* Not more than max_len bytes (12 or 16) */
 
@@ -129,9 +133,9 @@ int make_filesystem(
                                                        "Don't know how to create read-only file system '%s', refusing.",
                                                        fstype);
         } else {
-                if (root)
+                if (root && !mkfs_supports_root_option(fstype))
                         return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP),
-                                               "Populating with source tree is only supported for read-only filesystems");
+                                               "Populating with source tree is not supported for %s", fstype);
                 r = mkfs_exists(fstype);
                 if (r < 0)
                         return log_error_errno(r, "Failed to determine whether mkfs binary for %s exists: %m", fstype);
@@ -171,7 +175,7 @@ int make_filesystem(
                 assert_se(sd_id128_to_uuid_string(uuid, vol_id));
 
         /* When changing this conditional, also adjust the log statement below. */
-        if (streq(fstype, "ext2"))
+        if (streq(fstype, "ext2")) {
                 argv = strv_new(mkfs,
                                 "-q",
                                 "-L", label,
@@ -180,8 +184,16 @@ int make_filesystem(
                                 "-m", "0",
                                 "-E", discard ? "discard,lazy_itable_init=1" : "nodiscard,lazy_itable_init=1",
                                 node);
+                if (!argv)
+                        return log_oom();
 
-        else if (STR_IN_SET(fstype, "ext3", "ext4"))
+                if (root) {
+                        r = strv_extend_strv(&argv, STRV_MAKE("-d", root), false);
+                        if (r < 0)
+                                return log_oom();
+                }
+
+        } else if (STR_IN_SET(fstype, "ext3", "ext4")) {
                 argv = strv_new(mkfs,
                                 "-q",
                                 "-L", label,
@@ -192,7 +204,13 @@ int make_filesystem(
                                 "-E", discard ? "discard,lazy_itable_init=1" : "nodiscard,lazy_itable_init=1",
                                 node);
 
-        else if (streq(fstype, "btrfs")) {
+                if (root) {
+                        r = strv_extend_strv(&argv, STRV_MAKE("-d", root), false);
+                        if (r < 0)
+                                return log_oom();
+                }
+
+        } else if (streq(fstype, "btrfs")) {
                 argv = strv_new(mkfs,
                                 "-q",
                                 "-L", label,
@@ -207,6 +225,12 @@ int make_filesystem(
                                 return log_oom();
                 }
 
+                if (root) {
+                        r = strv_extend_strv(&argv, STRV_MAKE("-r", root), false);
+                        if (r < 0)
+                                return log_oom();
+                }
+
         } else if (streq(fstype, "f2fs")) {
                 argv = strv_new(mkfs,
                                 "-q",

src/shared/mkfs-util.h

@@ -9,4 +9,6 @@
 
 int mkfs_exists(const char *fstype);
 
+int mkfs_supports_root_option(const char *fstype);
+
 int make_filesystem(const char *node, const char *fstype, const char *label, const char *root, sd_id128_t uuid, bool discard);