btrfs-progs: rescue: Introduce fix-device-size

Introduce new subcommand 'fix-device-size' to the rescue group, to fix
device size alignment-related problems.

Especially for people unable to mount their fs with super::total_bytes
mismatch, this tool will fix the problems and let the mount continue.

Reported-by: Asif Youssuff <yoasif@gmail.com>
Reported-by: Rich Rauenzahn <rrauenza@gmail.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>

Documentation/btrfs-rescue.asciidoc

@@ -73,6 +73,35 @@ the log and the filesystem may be mounted normally again. The keywords to look
 for are 'open_ctree' which says that it's during mount and function names
 that contain 'replay', 'recover' or 'log_tree'.
 
+*fix-device-size* <device>::
+fix device size and super block total bytes
++
+This command will fix the following problems, by re-aligning all devices' total
+bytes and re-calculating super block total bytes.
++
+1. Newer kernel refuse to mount btrfs caused by mismatch super block total bytes
++
+----
+BTRFS error (device sdb): super_total_bytes 92017859088384 mismatch with fs_devices total_rw_bytes 92017859094528
+----
++
+2. Noisy kernel warning for newer kernels
++
+----
+WARNING: CPU: 3 PID: 439 at fs/btrfs/ctree.h:1559 btrfs_update_device+0x1c5/0x1d0 [btrfs]
+----
++
+And the corresponding line is the `WARN_ON()` line below:
++
+----
+{
+	BUILD_BUG_ON(sizeof(u64) !=
+		     sizeof(((struct btrfs_dev_item *)0))->total_bytes);
+	WARN_ON(!IS_ALIGNED(val, eb->fs_info->sectorsize));
+	btrfs_set_64(eb, s, offsetof(struct btrfs_dev_item, total_bytes), val);
+}
+----
+
 EXIT STATUS
 -----------
 *btrfs rescue* returns a zero exit status if it succeeds. Non zero is

cmds-rescue.c

@@ -20,6 +20,7 @@
 
 #include <getopt.h>
 #include "ctree.h"
+#include "volumes.h"
 #include "transaction.h"
 #include "disk-io.h"
 #include "commands.h"
@@ -202,6 +203,51 @@ out:
 	return !!ret;
 }
 
+static const char * const cmd_rescue_fix_device_size_usage[] = {
+	"btrfs rescue fix-device-size <device>",
+	"Re-align device and super block sizes. Usable if newer kernel refuse to mount it due to mismatch super size",
+	"",
+	NULL
+};
+
+static int cmd_rescue_fix_device_size(int argc, char **argv)
+{
+	struct btrfs_fs_info *fs_info;
+	char *devname;
+	int ret;
+
+	clean_args_no_options(argc, argv, cmd_rescue_fix_device_size_usage);
+
+	if (check_argc_exact(argc, 2))
+		usage(cmd_rescue_fix_device_size_usage);
+
+	devname = argv[optind];
+	ret = check_mounted(devname);
+	if (ret < 0) {
+		error("could not check mount status: %s", strerror(-ret));
+		goto out;
+	} else if (ret) {
+		error("%s is currently mounted", devname);
+		ret = -EBUSY;
+		goto out;
+	}
+
+	fs_info = open_ctree_fs_info(devname, 0, 0, 0, OPEN_CTREE_WRITES |
+				     OPEN_CTREE_PARTIAL);
+	if (!fs_info) {
+		error("could not open btrfs");
+		ret = -EIO;
+		goto out;
+	}
+
+	ret = btrfs_fix_device_and_super_size(fs_info);
+	if (ret > 0)
+		ret = 0;
+	close_ctree(fs_info->tree_root);
+out:
+	return !!ret;
+}
+
 static const char rescue_cmd_group_info[] =
 "toolbox for specific rescue operations";
 
@@ -212,6 +258,8 @@ const struct cmd_group rescue_cmd_group = {
 		{ "super-recover", cmd_rescue_super_recover,
 			cmd_rescue_super_recover_usage, NULL, 0},
 		{ "zero-log", cmd_rescue_zero_log, cmd_rescue_zero_log_usage, NULL, 0},
+		{ "fix-device-size", cmd_rescue_fix_device_size,
+			cmd_rescue_fix_device_size_usage, NULL, 0},
 		NULL_CMD_STRUCT
 	}
 };

volumes.c

@@ -2477,3 +2477,60 @@ int btrfs_fix_super_size(struct btrfs_fs_info *fs_info)
 		old_bytes, total_bytes);
 	return 1;
 }
+
+/*
+ * Return 0 if all devices and super block sizes are good
+ * Return >0 if any device/super size problem was found, but fixed
+ * Return <0 if something wrong happened during fixing
+ */
+int btrfs_fix_device_and_super_size(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_device *device;
+	struct list_head *dev_list = &fs_info->fs_devices->devices;
+	bool have_bad_value = false;
+	int ret;
+
+	/* Seed device is not supported yet */
+	if (fs_info->fs_devices->seed) {
+		error("fixing device size with seed device is not supported yet");
+		return -EOPNOTSUPP;
+	}
+
+	/* All devices must be set up before repairing */
+	if (list_empty(dev_list)) {
+		error("no device found");
+		return -ENODEV;
+	}
+	list_for_each_entry(device, dev_list, dev_list) {
+		if (device->fd == -1 || !device->writeable) {
+			error("devid %llu is missing or not writeable",
+			      device->devid);
+			error(
+	"fixing device size needs all device(s) to be present and writeable");
+			return -ENODEV;
+		}
+	}
+
+	/* Repair total_bytes of each device */
+	list_for_each_entry(device, dev_list, dev_list) {
+		ret = btrfs_fix_device_size(fs_info, device);
+		if (ret < 0)
+			return ret;
+		if (ret > 0)
+			have_bad_value = true;
+	}
+
+	/* Repair super total_byte */
+	ret = btrfs_fix_super_size(fs_info);
+	if (ret > 0)
+		have_bad_value = true;
+	if (have_bad_value) {
+		printf(
+	"Fixed unaligned/mismatched total_bytes for super block and device items\n");
+		ret = 1;
+	} else {
+		printf("No device size related problem found\n");
+		ret = 0;
+	}
+	return ret;
+}

volumes.h

@@ -248,4 +248,5 @@ u64 btrfs_stripe_length(struct btrfs_fs_info *fs_info,
 int btrfs_fix_device_size(struct btrfs_fs_info *fs_info,
 			  struct btrfs_device *device);
 int btrfs_fix_super_size(struct btrfs_fs_info *fs_info);
+int btrfs_fix_device_and_super_size(struct btrfs_fs_info *fs_info);
 #endif