Add the "btrfs filesystem label" command

Hi all,

this patch adds the command "btrfs filesystem label" to change (or show) the
label of a filesystem.
This patch is a subset of the one written previously by Morey Roof. I
included the user space part only. So it is possible only to change/show a
label of a *single device* and *unounted* filesystem.

The reason of excluding the kernel space part, is to simplify the patch in
order to speed the check and then the merging of the patch itself. In fact I
have to point out that in the past there was almost three attempts to propose
this patch, without success neither complaints.

Chris, let me know how you want to proceed. I know that you are very busy,
and you prefer to work to stabilize btrfs instead adding new feature. But I
think that changing a label is a *essential* feature for a filesystem
managing tool. Think about a mount by LABEL.

To show a label

$ btrfs filesystem label <device>

To set a label

$ btrfs filesystem label <device> <newlabel>

Please guys, give a look to the source.
Comments are welcome.

You can pull the source from the branch "label" of the repository
http://cassiopea.homelinux.net/git/btrfs-progs-unstable.git

Regards
G.Baroncelli

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 121 insertions, 0 deletions

diff --git a/btrfslabel.c b/btrfslabel.c
new file mode 100644
index 00000000..c9f46844
--- /dev/null
+++ b/btrfslabel.c
@@ -0,0 +1,121 @@
+/*
+ * Copyright (C) 2008 Morey Roof.   All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#define _GNU_SOURCE
+
+#ifndef __CHECKER__
+#include <sys/ioctl.h>
+#include <sys/mount.h>
+#include "ioctl.h"
+#endif /* __CHECKER__ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <dirent.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <linux/fs.h>
+#include <linux/limits.h>
+#include <ctype.h>
+#include "kerncompat.h"
+#include "ctree.h"
+#include "utils.h"
+#include "version.h"
+#include "disk-io.h"
+#include "transaction.h"
+
+#define MOUNTED                        1
+#define UNMOUNTED                      2
+#define GET_LABEL                      3
+#define SET_LABEL                      4
+
+static void change_label_unmounted(char *dev, char *nLabel)
+{
+       struct btrfs_root *root;
+       struct btrfs_trans_handle *trans;
+
+       /* Open the super_block at the default location
+        * and as read-write.
+        */
+       root = open_ctree(dev, 0, 1);
+
+       trans = btrfs_start_transaction(root, 1);
+       strncpy(root->fs_info->super_copy.label, nLabel, BTRFS_LABEL_SIZE);
+       btrfs_commit_transaction(trans, root);
+
+       /* Now we close it since we are done. */
+       close_ctree(root);
+}
+
+static void get_label_unmounted(char *dev)
+{
+       struct btrfs_root *root;
+
+       /* Open the super_block at the default location
+        * and as read-only.
+        */
+       root = open_ctree(dev, 0, 0);
+
+       fprintf(stdout, "%s\n", root->fs_info->super_copy.label);
+
+       /* Now we close it since we are done. */
+       close_ctree(root);
+}
+
+int get_label(char *btrfs_dev)
+{
+
+	int ret;
+	ret = check_mounted(btrfs_dev);
+	if (ret < 0)
+	{
+	       fprintf(stderr, "FATAL: error checking %s mount status\n", btrfs_dev);
+	       return -1;
+	}
+
+	if(ret != 0)
+	{
+	       fprintf(stderr, "FATAL: the filesystem has to be unmounted\n");
+	       return -2;
+	}
+	get_label_unmounted(btrfs_dev);
+	return 0;
+}
+
+
+int set_label(char *btrfs_dev, char *nLabel)
+{
+
+	int ret;
+	ret = check_mounted(btrfs_dev);
+	if (ret < 0)
+	{
+	       fprintf(stderr, "FATAL: error checking %s mount status\n", btrfs_dev);
+	       return -1;
+	}
+
+	if(ret != 0)
+	{
+	       fprintf(stderr, "FATAL: the filesystem has to be unmounted\n");
+	       return -2;
+	}
+	change_label_unmounted(btrfs_dev, nLabel);
+	return 0;
+}