Btrfs: check write access to mount earlier while creating snapshots

Move check of write access to mount into upper functions so that we can
use mnt_want_write_file instead, which is faster than mnt_want_write.

Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 3a3f916..c1f4975 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -652,13 +652,9 @@ static noinline int btrfs_mksubvol(struct path *parent,
        if (dentry->d_inode)
                goto out_dput;
 
-       error = mnt_want_write(parent->mnt);
-       if (error)
-               goto out_dput;
-
        error = btrfs_may_create(dir, dentry);
        if (error)
-               goto out_drop_write;
+               goto out_dput;
 
        down_read(&BTRFS_I(dir)->root->fs_info->subvol_sem);
 
@@ -676,8 +672,6 @@ static noinline int btrfs_mksubvol(struct path *parent,
                fsnotify_mkdir(dir, dentry);
 out_up_read:
        up_read(&BTRFS_I(dir)->root->fs_info->subvol_sem);
-out_drop_write:
-       mnt_drop_write(parent->mnt);
 out_dput:
        dput(dentry);
 out_unlock:
@@ -1395,16 +1389,20 @@ static noinline int btrfs_ioctl_snap_create_transid(struct file *file,
        if (root->fs_info->sb->s_flags & MS_RDONLY)
                return -EROFS;
 
+       ret = mnt_want_write_file(file);
+       if (ret)
+               goto out;
+
        namelen = strlen(name);
        if (strchr(name, '/')) {
                ret = -EINVAL;
-               goto out;
+               goto out_drop_write;
        }
 
        if (name[0] == '.' &&
           (namelen == 1 || (name[1] == '.' && namelen == 2))) {
                ret = -EEXIST;
-               goto out;
+               goto out_drop_write;
        }
 
        if (subvol) {
@@ -1415,7 +1413,7 @@ static noinline int btrfs_ioctl_snap_create_transid(struct file *file,
                src_file = fget(fd);
                if (!src_file) {
                        ret = -EINVAL;
-                       goto out;
+                       goto out_drop_write;
                }
 
                src_inode = src_file->f_path.dentry->d_inode;
@@ -1424,13 +1422,15 @@ static noinline int btrfs_ioctl_snap_create_transid(struct file *file,
                               "another FS\n");
                        ret = -EINVAL;
                        fput(src_file);
-                       goto out;
+                       goto out_drop_write;
                }
                ret = btrfs_mksubvol(&file->f_path, name, namelen,
                                     BTRFS_I(src_inode)->root,
                                     transid, readonly);
                fput(src_file);
        }
+out_drop_write:
+       mnt_drop_write_file(file);
 out:
        return ret;
 }