Btrfs: Add a new ioctl to get the label of a mounted file system

Add a new ioctl(2) BTRFS_IOC_GET_FSLABLE, so that we can get the label upon a mounted filesystem.

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

1 files changed, 21 insertions, 0 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index d02ec577f70f..fcc15a6804a9 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3917,6 +3917,25 @@ out:
         return ret;
 }
 
+static int btrfs_ioctl_get_fslabel(struct file *file, void __user *arg)
+{
+        struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
+        const char *label = root->fs_info->super_copy->label;
+        size_t len = strnlen(label, BTRFS_LABEL_SIZE);
+        int ret;
+
+        if (len == BTRFS_LABEL_SIZE) {
+                pr_warn("btrfs: label is too long, return the first %zu bytes\n",
+                        --len);
+        }
+
+        mutex_lock(&root->fs_info->volume_mutex);
+        ret = copy_to_user(arg, label, len);
+        mutex_unlock(&root->fs_info->volume_mutex);
+
+        return ret ? -EFAULT : 0;
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
                 cmd, unsigned long arg)
 {
@@ -4017,6 +4036,8 @@ long btrfs_ioctl(struct file *file, unsigned int
                 return btrfs_ioctl_qgroup_limit(file, argp);
         case BTRFS_IOC_DEV_REPLACE:
                 return btrfs_ioctl_dev_replace(root, argp);
+        case BTRFS_IOC_GET_FSLABEL:
+                return btrfs_ioctl_get_fslabel(file, argp);
         }
 
         return -ENOTTY;