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>

Makefile

@@ -4,7 +4,7 @@ CFLAGS = -g -Werror -Os
 objects = ctree.o disk-io.o radix-tree.o extent-tree.o print-tree.o \
 	  root-tree.o dir-item.o file-item.o inode-item.o \
 	  inode-map.o crc32c.o rbtree.o extent-cache.o extent_io.o \
-	  volumes.o utils.o btrfs-list.o
+	  volumes.o utils.o btrfs-list.o btrfslabel.o
 
 #
 CHECKFLAGS=-D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ -Wbitwise \

btrfs.c

@@ -108,11 +108,6 @@ static struct Command commands[] = {
 	  "device delete", "<device> [<device>...] <path>\n"
 		"Remove a device from a filesystem."
 	},
-	/* coming soon
-	{ 2, "filesystem label", "<label> <path>\n"
-		"Set the label of a filesystem"
-	}
-	*/
 	{ 0, 0 , 0 }
 };
 

btrfs_cmds.c

@@ -40,6 +40,7 @@
 #include "volumes.h"
 
 #include "btrfs_cmds.h"
+#include "btrfslabel.h"
 
 #ifdef __CHECKER__
 #define BLKGETSIZE64 0
@@ -874,6 +875,21 @@ int do_set_default_subvol(int nargs, char **argv)
 	return 0;
 }
 
+int do_change_label(int nargs, char **argv)
+{
+	/* check the number of argument */
+	if ( nargs > 3 ){
+		fprintf(stderr, "ERROR: '%s' requires maximum 2 args\n",
+			argv[0]);
+		return -2;
+	}else if (nargs == 2){
+		return get_label(argv[1]);
+	} else {	/* nargs == 0 */
+		return set_label(argv[1], argv[2]);
+	}
+}
+
+
 int do_df_filesystem(int nargs, char **argv)
 {
 	struct btrfs_ioctl_space_args *sargs;

btrfs_cmds.h

@@ -32,3 +32,4 @@ int list_subvols(int fd);
 int do_df_filesystem(int nargs, char **argv);
 int find_updated_files(int fd, u64 root_id, u64 oldest_gen);
 int do_find_newer(int argc, char **argv);
+int do_change_label(int argc, char **argv);

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;
+}

btrfslabel.h

@@ -0,0 +1,5 @@
+/* btrflabel.h */
+
+
+int get_label(char *btrfs_dev);
+int set_label(char *btrfs_dev, char *nLabel);

man/btrfs.8.in

@@ -19,6 +19,8 @@ btrfs \- control a btrfs filesystem
 .PP
 \fBbtrfs\fP \fBfilesystem resize\fP\fI [+/\-]<size>[gkm]|max <filesystem>\fP
 .PP
+\fBbtrfs\fP \fBfilesystem label\fP\fI <dev> [newlabel]\fP
+.PP
 \fBbtrfs\fP \fBfilesystem defrag\fP\fI [options] <file>|<dir> [<file>|<dir>...]\fP
 .PP
 \fBbtrfs\fP \fBsubvolume find-new\fP\fI <subvolume> <last_gen>\fP
@@ -164,6 +166,23 @@ can expand the partition before enlarging the filesystem and shrink the
 partition after reducing the size of the filesystem.
 .TP
 
+\fBbtrfs\fP \fBfilesystem label\fP\fI <dev> [newlabel]\fP
+Show or update the label of a filesystem. \fI<dev>\fR is used to identify the
+filesystem. 
+If a \fInewlabel\fR optional argument is passed, the label is changed. The
+following costraints exist for a label:
+.IP
+- the maximum allowable lenght shall be less or equal than 256 chars
+.IP
+- the label shall not  contain the '/' or '\\' characters.
+
+NOTE: Currently there are the following limitations:
+.IP
+- the filesystem has to be unmounted
+.IP
+- the filesystem should not have more than one device.
+.TP
+
 \fBfilesystem show\fR [<uuid>|<label>]\fR
 Show the btrfs filesystem with some additional info. If no UUID or label is
 passed, \fBbtrfs\fR show info of all the btrfs filesystem.

utils.c

@@ -812,6 +812,39 @@ out_mntloop_err:
 	return ret;
 }
 
+/* Gets the mount point of btrfs filesystem that is using the specified device.
+ * Returns 0 is everything is good, <0 if we have an error.
+ * TODO: Fix this fucntion and check_mounted to work with multiple drive BTRFS
+ * setups.
+ */
+int get_mountpt(char *dev, char *mntpt, size_t size)
+{
+       struct mntent *mnt;
+       FILE *f;
+       int ret = 0;
+
+       f = setmntent("/proc/mounts", "r");
+       if (f == NULL)
+               return -errno;
+
+       while ((mnt = getmntent(f)) != NULL )
+       {
+               if (strcmp(dev, mnt->mnt_fsname) == 0)
+               {
+                       strncpy(mntpt, mnt->mnt_dir, size);
+                       break;
+               }
+       }
+
+       if (mnt == NULL)
+       {
+               /* We didn't find an entry so lets report an error */
+               ret = -1;
+       }
+
+       return ret;
+}
+
 struct pending_dir {
 	struct list_head list;
 	char name[256];
@@ -1002,3 +1035,27 @@ char *pretty_sizes(u64 size)
 	return pretty;
 }
 
+/*
+ * Checks to make sure that the label matches our requirements.
+ * Returns:
+       0    if everything is safe and usable
+      -1    if the label is too long
+      -2    if the label contains an invalid character
+ */
+int check_label(char *input)
+{
+       int i;
+       int len = strlen(input);
+
+       if (len > BTRFS_LABEL_SIZE) {
+               return -1;
+       }
+
+       for (i = 0; i < len; i++) {
+               if (input[i] == '/' || input[i] == '\\') {
+                       return -2;
+               }
+       }
+
+       return 0;
+}

utils.h

@@ -40,4 +40,6 @@ int check_mounted(const char *devicename);
 int btrfs_device_already_in_root(struct btrfs_root *root, int fd,
 				 int super_offset);
 char *pretty_sizes(u64 size);
+int check_label(char *input);
+int get_mountpt(char *dev, char *mntpt, size_t size);
 #endif