Btrfs: set/change the label of a mounted file system

With this new ioctl(2) BTRFS_IOC_SET_FSLABEL, we can set/change the label of a mounted file system.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Miao Xie <miaox@cn.fujitsu.com>
Reviewed-by: Goffredo Baroncelli <kreijack@inwind.it>
Reviewed-by: David Sterba <dsterba@suse.cz>
Reviewed-by: Goffredo Baroncelli <kreijack@inwind.it>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

2 files changed, 44 insertions, 0 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index fcc15a6804a9..0f68729f261e 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3936,6 +3936,46 @@ static int btrfs_ioctl_get_fslabel(struct file *file, void __user *arg)
         return ret ? -EFAULT : 0;
 }
 
+static int btrfs_ioctl_set_fslabel(struct file *file, void __user *arg)
+{
+        struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
+        struct btrfs_super_block *super_block = root->fs_info->super_copy;
+        struct btrfs_trans_handle *trans;
+        char label[BTRFS_LABEL_SIZE];
+        int ret;
+
+        if (!capable(CAP_SYS_ADMIN))
+                return -EPERM;
+
+        if (copy_from_user(label, arg, sizeof(label)))
+                return -EFAULT;
+
+        if (strnlen(label, BTRFS_LABEL_SIZE) == BTRFS_LABEL_SIZE) {
+                pr_err("btrfs: unable to set label with more than %d bytes\n",
+                       BTRFS_LABEL_SIZE - 1);
+                return -EINVAL;
+        }
+
+        ret = mnt_want_write_file(file);
+        if (ret)
+                return ret;
+
+        mutex_lock(&root->fs_info->volume_mutex);
+        trans = btrfs_start_transaction(root, 0);
+        if (IS_ERR(trans)) {
+                ret = PTR_ERR(trans);
+                goto out_unlock;
+        }
+
+        strcpy(super_block->label, label);
+        ret = btrfs_end_transaction(trans, root);
+
+out_unlock:
+        mutex_unlock(&root->fs_info->volume_mutex);
+        mnt_drop_write_file(file);
+        return ret;
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
                 cmd, unsigned long arg)
 {
@@ -4038,6 +4078,8 @@ long btrfs_ioctl(struct file *file, unsigned int
                 return btrfs_ioctl_dev_replace(root, argp);
         case BTRFS_IOC_GET_FSLABEL:
                 return btrfs_ioctl_get_fslabel(file, argp);
+        case BTRFS_IOC_SET_FSLABEL:
+                return btrfs_ioctl_set_fslabel(file, argp);
         }
 
         return -ENOTTY;
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 51c0b335e0c8..fa3a5f9338fc 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -504,6 +504,8 @@ struct btrfs_ioctl_send_args {
                                struct btrfs_ioctl_qgroup_limit_args)
 #define BTRFS_IOC_GET_FSLABEL _IOR(BTRFS_IOCTL_MAGIC, 49, \
                                    char[BTRFS_LABEL_SIZE])
+#define BTRFS_IOC_SET_FSLABEL _IOW(BTRFS_IOCTL_MAGIC, 50, \
+                                   char[BTRFS_LABEL_SIZE])
 #define BTRFS_IOC_GET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 52, \
                                       struct btrfs_ioctl_get_dev_stats)
 #define BTRFS_IOC_DEV_REPLACE _IOWR(BTRFS_IOCTL_MAGIC, 53, \