Bug 1399487

Description of problem:

rear recover doesn't work when XFS is used for /boot from RHEL7.3.
grub2-install failed while 'rear recover' was executed in rescue.

  grub2-install: error: unknown filesystem.

grub2-probe --device <device file for /boot>
also shows the same error.

The error means that it could not detect the filesystem type of /boot partition.
/boot partition should be formatted with xfs to reproduce it.

From RHEL7.3, CRC feature was enabled for mkfs.xfs. It can be confirmed with the output of mkfs.xfs and xfs_info command.

# mkfs.xfs -f /dev/sdb1
meta-data=/dev/sdb1              isize=512    agcount=4, agsize=655296 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
... snip ...

# mount /dev/sdb1 /mnt
# xfs_info /mnt
meta-data=/dev/sdb1              isize=512    agcount=4, agsize=655296 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0 spinodes=0
... snip ...

In RHEL7.2, it outputs crc=0.

The manpage of mkfs.xfs was changed as below, so the change looks by intent.

  In RHEL7.2:
     By default, mkfs.xfs will not enable metadata CRCs.
  In RHEL7.3:
     By default, mkfs.xfs will enable metadata CRCs.

Also, the following statements are in the manpage of xfs_admin.

----------------------------------
       -U uuid
              Set  the UUID of the filesystem to uuid.  A sample UUID looks like this: "c1b9d5a2-f162-11cf-9ece-0020afc76f16".  The
              uuid may also be nil, which will set the filesystem UUID to the null UUID.  The uuid may also be generate, which will
              generate  a  new  UUID  for the filesystem.  Note that on CRC-enabled filesystems, this will set an incompatible flag
              such that older kernels will not be able to mount the filesystem.  To remove this  incompatible  flag,  use  restore,
              which will restore the original UUID and remove the incompatible feature flag as needed.
-----------------------------------

That says that an incompatible flag is set on CRC enabled.
And, the incompatible flag is checked in grub2-install with the following code, and it fails to detect XFS format.

In grub-core/fs/xfs.c:
static int grub_xfs_sb_valid(struct grub_xfs_data *data)
{
  grub_dprintf("xfs", "Validating superblock\n");
... snip ...
  if ((data->sblock.version & grub_cpu_to_be16_compile_time(XFS_SB_VERSION_NUMBITS)) ==
       grub_cpu_to_be16_compile_time(XFS_SB_VERSION_5))
    {
      grub_dprintf("xfs", "XFS v5 superblock detected\n");
      if (data->sblock.sb_features_incompat &
          grub_cpu_to_be32_compile_time(~XFS_SB_FEAT_INCOMPAT_SUPPORTED))
        {
          grub_error (GRUB_ERR_BAD_FS, "XFS filesystem has unsupported "
                      "incompatible features");
          return 0;
        }
      return 1;
    }

To sum up:
  - CRC feature of XFS was enabled by default from RHEL7.3
  - When CRC feature is enabled, xfs_admin -U command set an incompatible flag.
  - grub2-install fails to detect the filesystem as a valid and supporte XFS format.

In 'rear recover', the following commands are executed to format the /boot partition
  mkfs.xfs -f /dev/sda1
  xfs_admin -U <uuid> /dev/sda1

As a result, an incompatible flag is set in xfs_admin -U command.

If -m uuid=<uuid> option is used with mkfs.xfs, it seems that grub2-install doesn't fail.

XFS is the default filesystem from RHEL7. So, this is a serious regression.
This problem doesn't happen with RHEL7.2, since CRC feature is disabled by default.

Version-Release number of selected component (if applicable):
Red Hat Enterprise Linux 7.3

How reproducible:
Always


Steps to Reproduce:
1. Install RHEL7.3 (XFS for /boot)
2. configure local.conf, and run rear mkbackup
3. boot with rescue ISO (or ramdisk) and execute recovery.

Actual results:
The rear recover fails with grub2-install error.

Expected results:
The rear recover doesn't fail.

Addtional info:
I was not sure which component I should select for this bug, xfsprogs, grub2, and rear. The release note of 7.3 includes the following:
---------------------------
Metadata cyclic redundancy checks (CRCs) and directory entry file types are now enabled by default. To replicate the older mkfs on-disk format used in earlier versions of Red Hat Enterprise Linux 7, use the -m crc=0 -n ftype=0 options on the mkfs.xfs command line.
---------------------------
So, the CRC feature was enabled by intent, and I thought it's not a bug of xfsprogs, at least.