Final call for review of sb_bad_features2 in userspace

["Barry Naujok" <bnaujok@xxxxxxx>]

I think the attached patch maybe the least offensive for past
kernels, and XFSQA!

xfs_check and xfs_repair will ignore sb_bad_features2 if it is
zero, and if not, makes sure it's the same as sb_features2.

mkfs.xfs will set sb_bad_features2 to be the same. Maybe if
we change the behaviour of the kernel mount code with
respects of sb_bad_features2, this can be revisited.

(An intermediate solution I has was if "xfs_repair -n" is
run AND sb_bad_features is zero, then ignore it to let
xfs_repair continue, otherwise duplicate it, but doing
that requires a golden output change to QA 030 and 033
unless the kernel mount code is changed... ARGH!)

--

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

--- a/xfsprogs/db/check.c       2008-03-06 16:59:31.000000000 +1100
+++ b/xfsprogs/db/check.c       2008-03-06 12:32:54.664882390 +1100
@@ -869,6 +869,15 @@ blockget_f(
                                mp->m_sb.sb_frextents, frextents);
                error++;
        }
+       if (mp->m_sb.sb_bad_features2 != 0 &&
+                       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	2008-03-06 16:59:31.000000000 +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 2008-03-06 16:59:31.000000000 +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       2008-03-06 16:59:31.000000000 +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  2008-03-06 16:59:31.000000000 +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  2008-03-06 16:59:31.000000000 +1100
+++ b/xfsprogs/repair/phase1.c  2008-03-06 16:57:40.021125442 +1100
@@ -91,6 +91,20 @@ 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 != 0 &&
+                       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"));