btrfs: publish fs label in sysfs

This adds a writeable attribute which describes the label.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index ec631539111130d52a9604ea81d4ee669205dbbd..669fdf777b6cc5e7a47870e62a88a5d874476210 100644 (file)
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -355,6 +355,49 @@ static const struct attribute *allocation_attrs[] = {
        NULL,
 };
 
+static ssize_t btrfs_label_show(struct kobject *kobj,
+                               struct kobj_attribute *a, char *buf)
+{
+       struct btrfs_fs_info *fs_info = to_fs_info(kobj);
+       return snprintf(buf, PAGE_SIZE, "%s\n", fs_info->super_copy->label);
+}
+
+static ssize_t btrfs_label_store(struct kobject *kobj,
+                                struct kobj_attribute *a,
+                                const char *buf, size_t len)
+{
+       struct btrfs_fs_info *fs_info = to_fs_info(kobj);
+       struct btrfs_trans_handle *trans;
+       struct btrfs_root *root = fs_info->fs_root;
+       int ret;
+
+       if (len >= BTRFS_LABEL_SIZE) {
+               pr_err("btrfs: unable to set label with more than %d bytes\n",
+                      BTRFS_LABEL_SIZE - 1);
+               return -EINVAL;
+       }
+
+       trans = btrfs_start_transaction(root, 0);
+       if (IS_ERR(trans))
+               return PTR_ERR(trans);
+
+       spin_lock(&root->fs_info->super_lock);
+       strcpy(fs_info->super_copy->label, buf);
+       spin_unlock(&root->fs_info->super_lock);
+       ret = btrfs_commit_transaction(trans, root);
+
+       if (!ret)
+               return len;
+
+       return ret;
+}
+BTRFS_ATTR_RW(label, 0644, btrfs_label_show, btrfs_label_store);
+
+static struct attribute *btrfs_attrs[] = {
+       BTRFS_ATTR_PTR(label),
+       NULL,
+};
+
 static void btrfs_release_super_kobj(struct kobject *kobj)
 {
        struct btrfs_fs_info *fs_info = to_fs_info(kobj);
@@ -364,6 +407,7 @@ static void btrfs_release_super_kobj(struct kobject *kobj)
 static struct kobj_type btrfs_ktype = {
        .sysfs_ops      = &kobj_sysfs_ops,
        .release        = btrfs_release_super_kobj,
+       .default_attrs  = btrfs_attrs,
 };
 
 static inline struct btrfs_fs_info *to_fs_info(struct kobject *kobj)