mkfs: validate CoW 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_cowextsize_hint needs to check the hint value on a
simulated realtime file to make sure that it's correct.  This hasn't
been necessary in the past since one cannot have a CoW hint without a
reflink filesystem, and we previously didn't allow rt reflink
filesystems.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>

diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
index 64dad7070e8d6fed1a0ab6d92efd1b15f0049c7d..7b398e0440bb4049c80626d979aea65879686637 100644 (file)
--- a/mkfs/xfs_mkfs.c
+++ b/mkfs/xfs_mkfs.c
@@ -2882,6 +2882,26 @@ _("illegal CoW extent size hint %lld, must be less than %u.\n"),
                                min(XFS_MAX_BMBT_EXTLEN, mp->m_sb.sb_agblocks / 2));
                usage();
        }
+
+       /*
+        * 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 (!(cli->fsx.fsx_xflags & FS_XFLAG_RTINHERIT))
+               return;
+
+       fa = libxfs_inode_validate_cowextsize(mp, cli->fsx.fsx_cowextsize,
+                       S_IFREG, XFS_DIFLAG_REALTIME, flags2);
+
+       if (fa) {
+               fprintf(stderr,
+_("illegal CoW extent size hint %lld, must be less than %u and a multiple of %u. %p\n"),
+                               (long long)cli->fsx.fsx_cowextsize,
+                               min(XFS_MAX_BMBT_EXTLEN, mp->m_sb.sb_agblocks / 2),
+                               mp->m_sb.sb_rextsize, fa);
+               usage();
+       }
 }
 
 /* Complain if this filesystem is not a supported configuration. */