Re: [PATCH 2/2] btrfs-progs: canonicalize dm device name before update kernel

[Anand Jain <Anand.Jain@oracle.com>]

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 <anand.jain@oracle.com>
Date:   Thu Jul 3 18:22:05 2014 +0800

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


Thanks, Anand


On 14/08/2014 19:40, Eryu Guan wrote:
> 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 <guaneryu@gmail.com>
> ---
>
> 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);
>   		}
>   	}
>