Btrfs-progs: add a btrfs-select-super command to overwrite the super

Btrfs stores multiple copies of the superblock, and for common power-failure
crashes where barriers were not in use, one of the super copies is often
valid while the first copy is not.

This adds a btrfs-select-super -s N /dev/xxx command, which can
overwrite all the super blocks with a copy that you have already
determined is valid with btrfsck -s

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

Makefile

@@ -62,6 +62,9 @@ btrfs-debug-tree: $(objects) debug-tree.o
 btrfs-zero-log: $(objects) btrfs-zero-log.o
 	gcc $(CFLAGS) -o btrfs-zero-log $(objects) btrfs-zero-log.o $(LDFLAGS) $(LIBS)
 
+btrfs-select-super: $(objects) btrfs-select-super.o
+	gcc $(CFLAGS) -o btrfs-select-super $(objects) btrfs-select-super.o $(LDFLAGS) $(LIBS)
+
 btrfstune: $(objects) btrfstune.o
 	gcc $(CFLAGS) -o btrfstune $(objects) btrfstune.o $(LDFLAGS) $(LIBS)
 

btrfs-select-super.c

@@ -0,0 +1,99 @@
+/*
+ * Copyright (C) 2007 Oracle.  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 _XOPEN_SOURCE 500
+#define _GNU_SOURCE 1
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include "kerncompat.h"
+#include "ctree.h"
+#include "disk-io.h"
+#include "print-tree.h"
+#include "transaction.h"
+#include "list.h"
+#include "version.h"
+#include "utils.h"
+
+static void print_usage(void)
+{
+	fprintf(stderr, "usage: btrfs-select-super -s number dev\n");
+	fprintf(stderr, "%s\n", BTRFS_BUILD_VERSION);
+	exit(1);
+}
+
+int main(int ac, char **av)
+{
+	struct btrfs_root *root;
+	int ret;
+	int num;
+	u64 bytenr = 0;
+
+	while(1) {
+		int c;
+		c = getopt(ac, av, "s:");
+		if (c < 0)
+			break;
+		switch(c) {
+			case 's':
+				num = atol(optarg);
+				bytenr = btrfs_sb_offset(num);
+				printf("using SB copy %d, bytenr %llu\n", num,
+				       (unsigned long long)bytenr);
+				break;
+			default:
+				print_usage();
+		}
+	}
+	ac = ac - optind;
+
+	if (ac != 1)
+		print_usage();
+
+	if (bytenr == 0) {
+		fprintf(stderr, "Please select the super copy with -s\n");
+		print_usage();
+	}
+
+	radix_tree_init();
+
+	if((ret = check_mounted(av[optind])) < 0) {
+		fprintf(stderr, "Could not check mount status: %s\n", strerror(ret));
+		return ret;
+	} else if(ret) {
+		fprintf(stderr, "%s is currently mounted. Aborting.\n", av[optind]);
+		return -EBUSY;
+	}
+
+	root = open_ctree(av[optind], bytenr, 1);
+
+	if (root == NULL)
+		return 1;
+
+	/* make the super writing code think we've read the first super */
+	root->fs_info->super_bytenr = BTRFS_SUPER_INFO_OFFSET;
+	ret = write_all_supers(root);
+
+	/* we don't close the ctree or anything, because we don't want a real
+	 * transaction commit.  We just want the super copy we pulled off the
+	 * disk to overwrite all the other copies
+	 */ 
+	return ret;
+}

disk-io.c

@@ -829,7 +829,7 @@ int write_dev_supers(struct btrfs_root *root, struct btrfs_super_block *sb,
 
 	if (root->fs_info->super_bytenr != BTRFS_SUPER_INFO_OFFSET) {
 		btrfs_set_super_bytenr(sb, root->fs_info->super_bytenr);
-
+printk("speiiiiiiiiiiiiiiiiiiiiiiiiiiiii\n");
 		crc = ~(u32)0;
 		crc = btrfs_csum_data(NULL, (char *)sb + BTRFS_CSUM_SIZE, crc,
 				      BTRFS_SUPER_INFO_SIZE - BTRFS_CSUM_SIZE);

disk-io.h

@@ -47,6 +47,7 @@ struct btrfs_root *open_ctree(const char *filename, u64 sb_bytenr, int writes);
 struct btrfs_root *open_ctree_fd(int fp, const char *path, u64 sb_bytenr,
 				 int writes);
 int close_ctree(struct btrfs_root *root);
+int write_all_supers(struct btrfs_root *root);
 int write_ctree_super(struct btrfs_trans_handle *trans,
 		      struct btrfs_root *root);
 int btrfs_read_dev_super(int fd, struct btrfs_super_block *sb, u64 sb_bytenr);