On 15/08/2014 12:30, Eryu Guan wrote:

On Fri, Aug 15, 2014 at 09:50:34AM +0800, Anand Jain wrote:

quoted

Eryu,

  btrfs dev scan -d option is there for legacy reasons. The new method
  is using libblkid to find btrfs devs.

    David/Zach, is it time to remove -d option ? or mention deprecated.


  But your test case show problem using btrfsck as well. thats nice!
  The fix for this is in the kernel, which would return busy
  if the device path is being updated when the device is mounted.
  Can you try with Chris integration branch ? mainly the patch..

-------------
commit 4e5c146442b23437d23a2bd81b95f13dfeaffe88
Author: Anand Jain [off-list ref]
Date:   Thu Jul 3 18:22:05 2014 +0800

     Btrfs: device_list_add() should not update list when mounted
-------------

Thanks Anand, this patch fixed the issue, btrfsck reports "Device or
resource busy" now.

  Thanks for testing.

[root@hp-dl388g8-01 ~]# btrfsck /dev/mapper/rhel_hp--dl388g8--01-btrfs--2
ERROR: device scan failed '/dev/dm-3' - Device or resource busy
Checking filesystem on /dev/mapper/rhel_hp--dl388g8--01-btrfs--2
UUID: 1104d6d6-2653-496b-8d67-184d522dd632
checking extents
checking free space cache
cache and super generation don't match, space cache will be invalidated
checking fs roots
checking csums
checking root refs
found 114688 bytes used err is 0
total csum bytes: 0
total tree bytes: 114688
total fs tree bytes: 32768
total extent tree bytes: 16384
btree space waste bytes: 108436
file data blocks allocated: 0
  referenced 0
Btrfs v3.12

But btrfsck is still scanning unrelated devices when checking a btrfs
with multiple devices. In my case, I was checking btrfs on lv btrfs-2,
but btrfs-1(dm-3) was scanned too.

  That's expected, as of now the only way to find a partner device is
  by scanning the available devices.

Anand

Hope my first patch could fix this issue in an expected way.

Thanks,
Eryu

quoted

Thanks, Anand


On 14/08/2014 19:40, Eryu Guan wrote:

quoted

A btrfsck or btrfs device scan -d operation could change the device
name of other mounted btrfs in kernel, if the other btrfs is on lvm
device.

Assume that we have two btrfs filesystems, kernel is 3.16.0-rc4+

[root@hp-dl388eg8-01 btrfs-progs]# btrfs fi show
Label: none  uuid: 1aba7da5-ce2b-4af0-a716-db732abc60b2
         Total devices 1 FS bytes used 384.00KiB
         devid    1 size 15.00GiB used 2.04GiB path /dev/mapper/rhel_hp--dl388eg8--01-testlv1

Label: none  uuid: 26ff4f12-f6d9-4cbc-aae2-57febeefde37
         Total devices 2 FS bytes used 112.00KiB
         devid    1 size 15.00GiB used 2.03GiB path /dev/mapper/rhel_hp--dl388eg8--01-testlv2
         devid    2 size 15.00GiB used 2.01GiB path /dev/mapper/rhel_hp--dl388eg8--01-testlv3

Btrfs v3.14.2

And testlv1 was mounted at /mnt/btrfs

[root@hp-dl388eg8-01 btrfs-progs]# df -TP /mnt/btrfs
Filesystem                                Type  1024-blocks  Used Available Capacity Mounted on
/dev/mapper/rhel_hp--dl388eg8--01-testlv1 btrfs    15728640   512  13602560       1% /mnt/btrfs

Now run btrfsck on testlv2 or btrfs device scan -d, which will scan
all btrfs devices and somehow change the device name.

[root@hp-dl388eg8-01 btrfs-progs]# btrfsck /dev/mapper/rhel_hp--dl388eg8--01-testlv2 >/dev/null 2>&1

[root@hp-dl388eg8-01 btrfs-progs]# df -TP /mnt/btrfs
Filesystem     Type  1024-blocks  Used Available Capacity Mounted on
/dev/dm-3      btrfs    15728640   512  13602560       1% /mnt/btrfs
[root@hp-dl388eg8-01 btrfs-progs]# btrfs fi show
Label: none  uuid: 1aba7da5-ce2b-4af0-a716-db732abc60b2
         Total devices 1 FS bytes used 384.00KiB
         devid    1 size 15.00GiB used 2.04GiB path /dev/dm-3

Label: none  uuid: 26ff4f12-f6d9-4cbc-aae2-57febeefde37
         Total devices 2 FS bytes used 112.00KiB
         devid    1 size 15.00GiB used 2.03GiB path /dev/mapper/rhel_hp--dl388eg8--01-testlv2
         devid    2 size 15.00GiB used 2.01GiB path /dev/mapper/rhel_hp--dl388eg8--01-testlv3

Btrfs v3.14.2

Now calling btrfs_register_one_device with canonicalized dm device name.

Signed-off-by: Eryu Guan <redacted>
---

With patch 1 applied, btrfsck won't change the device name,
but btrfs device scan -d still does.

  utils.c | 44 +++++++++++++++++++++++++++++++++++++++++---
  1 file changed, 41 insertions(+), 3 deletions(-)

diff --git a/utils.c b/utils.c
index f54e749..3567094 100644
--- a/utils.c
+++ b/utils.c

@@ -985,6 +985,32 @@ static int blk_file_in_dev_list(struct btrfs_fs_devices* fs_devices,
  }

  /*
+ * Convert dm-N device name to /dev/mapper/name
+ */
+static void canonicalize_dm_name(char *devnode, char *path, int len)
+{
+	char *buf = NULL;
+	FILE *sysfsp = NULL;
+
+	buf = malloc(PATH_MAX);
+	if (!buf)
+		return;
+
+	snprintf(buf, PATH_MAX, "/sys/block/%s/dm/name", devnode);
+	sysfsp = fopen(buf, "r");
+	if (!sysfsp)
+		goto out;
+
+	if (fgets(buf, PATH_MAX, sysfsp)) {
+		buf[strlen(buf) - 1] = '\0';
+		snprintf(path, len - 1, "/dev/mapper/%s", buf);
+	}
+	fclose(sysfsp);
+out:
+	free(buf);
+}
+
+/*
   * returns 1 if the device was mounted, < 0 on error or 0 if everything
   * is safe to continue.
   */

@@ -1189,6 +1215,9 @@ again:
  		if (fsid && memcmp(fsid, tmp_devices->fsid, BTRFS_FSID_SIZE))
  			continue;
  		if (run_ioctl > 0) {
+			if (!strncmp(fullpath, "/dev/dm-", strlen("/dev/dm-")))
+				canonicalize_dm_name(dirent->d_name,
+						     fullpath, PATH_MAX);
  			btrfs_register_one_device(fullpath);
  		}
  		close(fd);

@@ -1475,8 +1504,11 @@ int btrfs_scan_block_devices(u8 *fsid, int run_ioctl)
  	int i;
  	char buf[1024];
  	char fullpath[110];
+	char devnode[64];
+	char *dirname = "/dev/";
  	int scans = 0;
  	int special;
+	int is_dm;

  scan_again:
  	proc_partitions = fopen("/proc/partitions","r");

@@ -1493,9 +1525,11 @@ scan_again:
  			return -ENOENT;
  		}

-	strcpy(fullpath,"/dev/");
-	while(fgets(buf, 1023, proc_partitions)) {
-		i = sscanf(buf," %*d %*d %*d %99s", fullpath+5);
+	strcpy(fullpath, dirname);
+	while (fgets(buf, sizeof(buf) - 1, proc_partitions)) {
+		i = sscanf(buf, " %*d %*d %*d %99s", devnode);
+		strncpy(fullpath + strlen(dirname), devnode,
+			sizeof(fullpath) - strlen(dirname));

  		/*
  		 * multipath and MD devices may register as a btrfs filesystem

@@ -1504,6 +1538,7 @@ scan_again:
  		 * This scans the special entries last
  		 */
  		special = strncmp(fullpath, "/dev/dm-", strlen("/dev/dm-")) == 0;
+		is_dm = special;
  		if (!special)
  			special = strncmp(fullpath, "/dev/md", strlen("/dev/md")) == 0;

@@ -1538,6 +1573,9 @@ scan_again:
  		if (fsid && memcmp(fsid, tmp_devices->fsid, BTRFS_FSID_SIZE))
  			continue;
  		if (run_ioctl > 0) {
+			if (is_dm)
+				canonicalize_dm_name(devnode, fullpath,
+						     sizeof(fullpath));
  			btrfs_register_one_device(fullpath);
  		}
  	}

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