mkfs: validate rt extent size hint when rtinherit is set

Extent size hints exist to nudge the behavior of the file data block
allocator towards trying to make aligned allocations.  Therefore, it
doesn't make sense to allow a hint that isn't a multiple of the
fundamental allocation unit for a given file.

This means that if the sysadmin is formatting with rtinherit set on the
root dir, validate_extsize_hint needs to check the hint value on a
simulated realtime file to make sure that it's correct.  Unfortunately,
the gate check here was for a nonzero rt extent size, which is wrong
since we never format with rtextsize==0.  This leads to absurd failures
such as:

# mkfs.xfs -f /dev/sdf -r extsize=7b -d rtinherit=0,extszinherit=13
illegal extent size hint 13, must be less than 649088 and a multiple of 7.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>

diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
index f84a42f9830c3a354439a797a8f56021d113cc04..9c14c04eae280b0a0988930f0081439ea93dfd88 100644 (file)
--- a/mkfs/xfs_mkfs.c
+++ b/mkfs/xfs_mkfs.c
@@ -2384,10 +2384,11 @@ _("illegal extent size hint %lld, must be less than %u.\n"),
        }
 
        /*
-        * Now we do it again with a realtime file so that we know the hint and
-        * flag that get passed on to realtime files will be correct.
+        * If the value is to be passed on to realtime files, revalidate with
+        * a realtime file so that we know the hint and flag that get passed on
+        * to realtime files will be correct.
         */
-       if (mp->m_sb.sb_rextsize == 0)
+       if (!(cli->fsx.fsx_xflags & FS_XFLAG_RTINHERIT))
                return;
 
        flags = XFS_DIFLAG_REALTIME;