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>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
index da83fb36a2438d91361fa64ab8db226fc87f0f7f..9dc71fb8c4c82af4fe844a75ecbadd09e3d4144e 100644 (file)
--- a/mkfs/xfs_mkfs.c
+++ b/mkfs/xfs_mkfs.c
@@ -2985,6 +2985,26 @@ _("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. */