Btrfs: fix subvolume mount by name problem when default mount subvolume is set

We create two subvolumes (meego_root and meego_home) in
btrfs root directory. And set meego_root as default mount
subvolume. After we remount btrfs, meego_root is mounted
to top directory by default. Then when we try to mount
meego_home (subvol=meego_home) to a subdirectory, it failed.
The problem is when default mount subvolume is set to
meego_root, we search meego_home in meego_root but can not find
it. So the solution is to add a new mount option (subvolrootid)
to specify subvol id of root and search subvol name in it. For
our case, now we can use "-o subvolrootid=0,subvol=meego_home)
to mount meego_home.

Detail information can be found in meego bugzilla:
https://bugs.meego.com/show_bug.cgi?id=15055

Signed-off-by: Zhong, Xin <xin.zhong@intel.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 33 insertions, 9 deletions

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 58e7de9cc90c..0ac712efcdf2 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -159,7 +159,7 @@ enum {
         Opt_compress_type, Opt_compress_force, Opt_compress_force_type,
         Opt_notreelog, Opt_ratio, Opt_flushoncommit, Opt_discard,
         Opt_space_cache, Opt_clear_cache, Opt_user_subvol_rm_allowed,
-        Opt_enospc_debug, Opt_err,
+        Opt_enospc_debug, Opt_subvolrootid, Opt_err,
 };
 
 static match_table_t tokens = {
@@ -189,6 +189,7 @@ static match_table_t tokens = {
         {Opt_clear_cache, "clear_cache"},
         {Opt_user_subvol_rm_allowed, "user_subvol_rm_allowed"},
         {Opt_enospc_debug, "enospc_debug"},
+        {Opt_subvolrootid, "subvolrootid=%d"},
         {Opt_err, NULL},
 };
 
@@ -232,6 +233,7 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
                         break;
                 case Opt_subvol:
                 case Opt_subvolid:
+                case Opt_subvolrootid:
                 case Opt_device:
                         /*
                          * These are parsed by btrfs_parse_early_options
@@ -388,7 +390,7 @@ out:
  */
 static int btrfs_parse_early_options(const char *options, fmode_t flags,
                 void *holder, char **subvol_name, u64 *subvol_objectid,
-                struct btrfs_fs_devices **fs_devices)
+                u64 *subvol_rootid, struct btrfs_fs_devices **fs_devices)
 {
         substring_t args[MAX_OPT_ARGS];
         char *opts, *orig, *p;
@@ -429,6 +431,18 @@ static int btrfs_parse_early_options(const char *options, fmode_t flags,
                                         *subvol_objectid = intarg;
                         }
                         break;
+                case Opt_subvolrootid:
+                        intarg = 0;
+                        error = match_int(&args[0], &intarg);
+                        if (!error) {
+                                /* we want the original fs_tree */
+                                if (!intarg)
+                                        *subvol_rootid =
+                                                BTRFS_FS_TREE_OBJECTID;
+                                else
+                                        *subvol_rootid = intarg;
+                        }
+                        break;
                 case Opt_device:
                         error = btrfs_scan_one_device(match_strdup(&args[0]),
                                         flags, holder, fs_devices);
@@ -736,6 +750,7 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
         fmode_t mode = FMODE_READ;
         char *subvol_name = NULL;
         u64 subvol_objectid = 0;
+        u64 subvol_rootid = 0;
         int error = 0;
 
         if (!(flags & MS_RDONLY))
@@ -743,7 +758,7 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
 
         error = btrfs_parse_early_options(data, mode, fs_type,
                                           &subvol_name, &subvol_objectid,
-                                          &fs_devices);
+                                          &subvol_rootid, &fs_devices);
         if (error)
                 return ERR_PTR(error);
 
@@ -807,15 +822,17 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
                 s->s_flags |= MS_ACTIVE;
         }
 
-        root = get_default_root(s, subvol_objectid);
-        if (IS_ERR(root)) {
-                error = PTR_ERR(root);
-                deactivate_locked_super(s);
-                goto error_free_subvol_name;
-        }
         /* if they gave us a subvolume name bind mount into that */
         if (strcmp(subvol_name, ".")) {
                 struct dentry *new_root;
+
+                root = get_default_root(s, subvol_rootid);
+                if (IS_ERR(root)) {
+                        error = PTR_ERR(root);
+                        deactivate_locked_super(s);
+                        goto error_free_subvol_name;
+                }
+
                 mutex_lock(&root->d_inode->i_mutex);
                 new_root = lookup_one_len(subvol_name, root,
                                       strlen(subvol_name));
@@ -836,6 +853,13 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
                 }
                 dput(root);
                 root = new_root;
+        } else {
+                root = get_default_root(s, subvol_objectid);
+                if (IS_ERR(root)) {
+                        error = PTR_ERR(root);
+                        deactivate_locked_super(s);
+                        goto error_free_subvol_name;
+                }
         }
 
         kfree(subvol_name);