===========================================================================
xfsprogs/db/check.c
===========================================================================

--- a/xfsprogs/db/check.c	2008-03-05 15:30:54.000000000 +1100
+++ b/xfsprogs/db/check.c	2008-03-05 15:28:58.638097511 +1100
@@ -869,6 +869,14 @@ blockget_f(
 				mp->m_sb.sb_frextents, frextents);
 		error++;
 	}
+	if (mp->m_sb.sb_bad_features2 != mp->m_sb.sb_features2) {
+		if (!sflag)
+			dbprintf("sb_features2 (0x%x) not same as "
+				"sb_bad_features2 (0x%x)\n",
+				mp->m_sb.sb_features2,
+				mp->m_sb.sb_bad_features2);
+		error++;
+	}
 	if ((sbversion & XFS_SB_VERSION_ATTRBIT) &&
 	    !XFS_SB_VERSION_HASATTR(&mp->m_sb)) {
 		if (!sflag)

===========================================================================
xfsprogs/db/sb.c
===========================================================================

--- a/xfsprogs/db/sb.c	2008-03-05 15:30:54.000000000 +1100
+++ b/xfsprogs/db/sb.c	2008-02-29 17:16:33.770423296 +1100
@@ -108,6 +108,7 @@ const field_t	sb_flds[] = {
 	{ "logsectsize", FLDT_UINT16D, OI(OFF(logsectsize)), C1, 0, TYP_NONE },
 	{ "logsunit", FLDT_UINT32D, OI(OFF(logsunit)), C1, 0, TYP_NONE },
 	{ "features2", FLDT_UINT32X, OI(OFF(features2)), C1, 0, TYP_NONE },
+	{ "bad_features2", FLDT_UINT32X, OI(OFF(bad_features2)), C1, 0, TYP_NONE },
 	{ NULL }
 };
 

===========================================================================
xfsprogs/include/xfs_sb.h
===========================================================================

--- a/xfsprogs/include/xfs_sb.h	2008-03-05 15:30:54.000000000 +1100
+++ b/xfsprogs/include/xfs_sb.h	2008-02-29 17:16:33.814417687 +1100
@@ -151,6 +151,7 @@ typedef struct xfs_sb
 	__uint16_t	sb_logsectsize;	/* sector size for the log, bytes */
 	__uint32_t	sb_logsunit;	/* stripe unit size for the log */
 	__uint32_t	sb_features2;	/* additional feature bits */
+	__uint32_t	sb_bad_features2; /* unusable space */
 } xfs_sb_t;
 
 /*
@@ -169,7 +170,7 @@ typedef enum {
 	XFS_SBS_GQUOTINO, XFS_SBS_QFLAGS, XFS_SBS_FLAGS, XFS_SBS_SHARED_VN,
 	XFS_SBS_INOALIGNMT, XFS_SBS_UNIT, XFS_SBS_WIDTH, XFS_SBS_DIRBLKLOG,
 	XFS_SBS_LOGSECTLOG, XFS_SBS_LOGSECTSIZE, XFS_SBS_LOGSUNIT,
-	XFS_SBS_FEATURES2,
+	XFS_SBS_FEATURES2, XFS_SBS_BAD_FEATURES2,
 	XFS_SBS_FIELDCOUNT
 } xfs_sb_field_t;
 

===========================================================================
xfsprogs/libxfs/xfs_mount.c
===========================================================================

--- a/xfsprogs/libxfs/xfs_mount.c	2008-03-05 15:30:54.000000000 +1100
+++ b/xfsprogs/libxfs/xfs_mount.c	2008-02-29 17:16:33.834415138 +1100
@@ -140,6 +140,7 @@ static struct {
     { offsetof(xfs_sb_t, sb_logsectsize),0 },
     { offsetof(xfs_sb_t, sb_logsunit),	 0 },
     { offsetof(xfs_sb_t, sb_features2),	 0 },
+    { offsetof(xfs_sb_t, sb_bad_features2), 0 },
     { sizeof(xfs_sb_t),			 0 }
 };
 

===========================================================================
xfsprogs/mkfs/xfs_mkfs.c
===========================================================================

--- a/xfsprogs/mkfs/xfs_mkfs.c	2008-03-05 15:30:54.000000000 +1100
+++ b/xfsprogs/mkfs/xfs_mkfs.c	2008-03-05 15:27:37.568461787 +1100
@@ -2103,6 +2103,13 @@ an AG size that is one stripe unit small
 			dirversion == 2, logversion == 2, attrversion == 1,
 			(sectorsize != BBSIZE || lsectorsize != BBSIZE),
 			sbp->sb_features2 != 0);
+	/*
+	 * Due to a structure alignment issue, sb_features2 ended up in one
+	 * of two locations, the second "incorrect" location represented by
+	 * the sb_bad_features2 field. To avoid older kernels mounting
+	 * filesystems they shouldn't, set both field to the same value.
+	 */
+	sbp->sb_bad_features2 = sbp->sb_features2;
 
 	if (force_overwrite)
 		zero_old_xfs_structures(&xi, sbp);

===========================================================================
xfsprogs/repair/phase1.c
===========================================================================

--- a/xfsprogs/repair/phase1.c	2008-03-05 15:30:54.000000000 +1100
+++ b/xfsprogs/repair/phase1.c	2008-03-05 15:19:09.513415413 +1100
@@ -91,6 +91,19 @@ phase1(xfs_mount_t *mp)
 		primary_sb_modified = 1;
 	}
 
+	/*
+	 * Check bad_features2 and make sure features2 the same as
+	 * bad_features (ORing the two together). Leave bad_features2
+	 * set so older kernels can still use it and not mount unsupported
+	 * filesystems when it reads bad_features2.
+	 */
+	if (sb->sb_bad_features2 != sb->sb_features2) {
+		sb->sb_features2 |= sb->sb_bad_features2;
+		sb->sb_bad_features2 = sb->sb_features2;
+		primary_sb_modified = 1;
+		do_warn(_("superblock has a features2 mismatch, correcting\n"));
+	}
+
 	if (primary_sb_modified)  {
 		if (!no_modify)  {
 			do_warn(_("writing modified primary superblock\n"));