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[PATCH 2/2 V2] xfsprogs: Add new sb_meta_uuid field, and userspace tools

To: Eric Sandeen <sandeen@xxxxxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>
Subject: [PATCH 2/2 V2] xfsprogs: Add new sb_meta_uuid field, and userspace tools to manipulate it
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Fri, 08 May 2015 16:49:25 -0500
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <554D23B2.4030103@xxxxxxxxxxx>
References: <554D1F56.7030209@xxxxxxxxxx> <554D23B2.4030103@xxxxxxxxxxx>
This adds a new superblock field, sb_meta_uuid.  This allows us to
change the use-visible UUID on crc-enabled filesytems from userspace
if desired, by copying the existing UUID to the new location for
metadata comparisons.  If this is done, an incompat flag must be
set to prevent older filesystems from mounting the filesystem, but
the original UUID can be restored, and the incompat flag removed,
with a new xfs_db / xfs_admin UUID command, "restore."

Much of this patch mirrors the kernel patch in simply renaming
the field used for metadata uuid comparison; other bits:

* Teach xfs_db to print the new meta_uuid field
* Allow xfs_db to generate a new UUID for CRC-enabled filesystems
* Allow xfs_db to revert to the original UUID and clear the flag
* Fix up xfs_copy to work with CRC-enabled filesystems
* Update the xfs_admin manpage to show the UUID "generate" command

Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
---

V2: initialize meta_uuid at mkfs time, libxfs expects this to be as
if read from disk w/o the META_UUID incompat flag, and copied to
the meta_uuid field.

Breaking it into libxfs & tools is actually more intricate than I thought,
so skipping it unless really desired.  ;)

Right now xfs_db "uuid restore" squawks if called on a filesystem that
doesn't need it; perhaps that should be removed...

I'm not totally sold on the "restore" command name either; open to
suggestions.

diff --git a/copy/xfs_copy.c b/copy/xfs_copy.c
index 279527c..a58eee5 100644
--- a/copy/xfs_copy.c
+++ b/copy/xfs_copy.c
@@ -466,6 +466,34 @@ write_wbuf(void)
        sighold(SIGCHLD);
 }
 
+void
+sb_update_uuid(
+       xfs_sb_t        *sb,
+       ag_header_t     *ag_hdr,
+       thread_args     *tcarg)
+{
+       /*
+        * If this filesystem has CRCs, the original UUID is stamped into
+        * all metadata.  We need to copy the original UUID into the meta_uuid
+        * slot and set the incompat flag if that hasn't already been done.
+        */
+       if (xfs_sb_version_hascrc(sb) && !xfs_sb_version_hasmetauuid(sb)) {
+               __be32 feat;
+
+               feat = be32_to_cpu(ag_hdr->xfs_sb->sb_features_incompat);
+               feat |= XFS_SB_FEAT_INCOMPAT_META_UUID;
+               ag_hdr->xfs_sb->sb_features_incompat = cpu_to_be32(feat);
+               platform_uuid_copy(&ag_hdr->xfs_sb->sb_meta_uuid,
+                                  &ag_hdr->xfs_sb->sb_uuid);
+       }
+
+       platform_uuid_copy(&ag_hdr->xfs_sb->sb_uuid, &tcarg->uuid);
+
+       /* We changed the UUID, so update the superblock CRC if needed */
+       if (xfs_sb_version_hascrc(sb))
+               xfs_update_cksum((char *)&ag_hdr->xfs_sb, sb->sb_sectsize,
+                                                        XFS_SB_CRC_OFF);
+}
 
 int
 main(int argc, char **argv)
@@ -659,16 +687,6 @@ main(int argc, char **argv)
        sb = &mbuf.m_sb;
        libxfs_sb_from_disk(sb, XFS_BUF_TO_SBP(sbp));
 
-       /*
-        * For now, V5 superblock filesystems are not supported without -d;
-        * we do not have the infrastructure yet to fix CRCs when a new UUID
-        * is generated.
-        */
-       if (xfs_sb_version_hascrc(sb) && !duplicate) {
-               do_log(_("%s: Cannot yet copy V5 fs without '-d'\n"), progname);
-               exit(1);
-       }
-
        mp = libxfs_mount(&mbuf, sb, xargs.ddev, xargs.logdev, xargs.rtdev, 0);
        if (mp == NULL) {
                do_log(_("%s: %s filesystem failed to initialize\n"
@@ -1127,8 +1145,7 @@ main(int argc, char **argv)
                        /* do each thread in turn, each has its own UUID */
 
                        for (j = 0, tcarg = targ; j < num_targets; j++)  {
-                               platform_uuid_copy(&ag_hdr.xfs_sb->sb_uuid,
-                                                       &tcarg->uuid);
+                               sb_update_uuid(sb, &ag_hdr, tcarg);
                                do_write(tcarg);
                                tcarg++;
                        }
diff --git a/db/sb.c b/db/sb.c
index 23ec87c..6b5bab0 100644
--- a/db/sb.c
+++ b/db/sb.c
@@ -29,6 +29,8 @@
 #include "output.h"
 #include "init.h"
 
+#define uuid_equal(s,d)                (platform_uuid_compare((s),(d)) == 0)
+
 static int     sb_f(int argc, char **argv);
 static void     sb_help(void);
 static int     uuid_f(int argc, char **argv);
@@ -121,6 +123,7 @@ const field_t       sb_flds[] = {
        { "crc", FLDT_CRC, OI(OFF(crc)), C1, 0, TYP_NONE },
        { "pquotino", FLDT_INO, OI(OFF(pquotino)), C1, 0, TYP_INODE },
        { "lsn", FLDT_UINT64X, OI(OFF(lsn)), C1, 0, TYP_NONE },
+       { "meta_uuid", FLDT_UUID, OI(OFF(meta_uuid)), C1, 0, TYP_NONE },
        { NULL }
 };
 
@@ -324,6 +327,7 @@ do_uuid(xfs_agnumber_t agno, uuid_t *uuid)
 {
        xfs_sb_t        tsb;
        static uuid_t   uu;
+       __int64_t       fields = XFS_SB_UUID;
 
        if (!get_sb(agno, &tsb))
                return NULL;
@@ -333,9 +337,38 @@ do_uuid(xfs_agnumber_t agno, uuid_t *uuid)
                pop_cur();
                return &uu;
        }
+
        /* set uuid */
+       if (!xfs_sb_version_hascrc(&tsb))
+               goto write;
+       /*
+        * If we have CRCs, and this UUID differs from that stamped in the
+        * metadata, set the incompat flag and copy the old one to the
+        * metadata-specific location.
+        *
+        * If we are setting the user-visible UUID back to match the metadata
+        * UUID, clear the metadata-specific location and the incompat flag.
+        */
+       if (!xfs_sb_version_hasmetauuid(&tsb) &&
+           !uuid_equal(uuid, &mp->m_sb.sb_meta_uuid)) {
+               mp->m_sb.sb_features_incompat |= XFS_SB_FEAT_INCOMPAT_META_UUID;
+               tsb.sb_features_incompat |= XFS_SB_FEAT_INCOMPAT_META_UUID;
+               memcpy(&tsb.sb_meta_uuid, &tsb.sb_uuid, sizeof(uuid_t));
+               fields |= XFS_SB_META_UUID | XFS_SB_FEATURES_INCOMPAT;
+       } else if (xfs_sb_version_hasmetauuid(&tsb) &&
+                  uuid_equal(uuid, &mp->m_sb.sb_meta_uuid)) {
+               memset(&tsb.sb_meta_uuid, 0, sizeof(uuid_t));
+               /* Write those zeros now; it's ignored once we clear the flag */
+               libxfs_sb_to_disk(iocur_top->data, &tsb, XFS_SB_META_UUID);
+               mp->m_sb.sb_features_incompat &=
+                                               ~XFS_SB_FEAT_INCOMPAT_META_UUID;
+               tsb.sb_features_incompat &= ~XFS_SB_FEAT_INCOMPAT_META_UUID;
+               fields |= XFS_SB_FEATURES_INCOMPAT;
+       }
+
+write:
        memcpy(&tsb.sb_uuid, uuid, sizeof(uuid_t));
-       libxfs_sb_to_disk(iocur_top->data, &tsb, XFS_SB_UUID);
+       libxfs_sb_to_disk(iocur_top->data, &tsb, fields);
        write_cur();
        return uuid;
 }
@@ -363,18 +396,6 @@ uuid_f(
                        return 0;
                }
 
-               /*
-                * For now, changing the UUID of V5 superblock filesystems is
-                * not supported; we do not have the infrastructure to fix all
-                * other metadata when a new superblock UUID is generated.
-                */
-               if (xfs_sb_version_hascrc(&mp->m_sb) &&
-                   strcasecmp(argv[1], "rewrite")) {
-                       dbprintf(_("%s: only 'rewrite' supported on V5 fs\n"),
-                               progname);
-                       return 0;
-               }
-
                if (!strcasecmp(argv[1], "generate")) {
                        platform_uuid_generate(&uu);
                } else if (!strcasecmp(argv[1], "nil")) {
@@ -388,6 +409,16 @@ uuid_f(
                        memcpy(&uu, uup, sizeof(uuid_t));
                        platform_uuid_unparse(&uu, bp);
                        dbprintf(_("old UUID = %s\n"), bp);
+               } else if (!strcasecmp(argv[1], "restore")) {
+                       xfs_sb_t        tsb;
+
+                       if (!get_sb(0, &tsb))
+                               return 0;
+                       if (!xfs_sb_version_hasmetauuid(&tsb)) {
+                               dbprintf(_("META_UUID not set"));
+                               return 0;
+                       }
+                       memcpy(&uu, mp->m_sb.sb_meta_uuid, sizeof(uuid_t));
                } else {
                        if (platform_uuid_parse(argv[1], &uu)) {
                                dbprintf(_("invalid UUID\n"));
@@ -658,6 +689,8 @@ version_string(
                strcat(s, ",CRC");
        if (xfs_sb_version_hasftype(sbp))
                strcat(s, ",FTYPE");
+       if (xfs_sb_version_hasmetauuid(sbp))
+               strcat(s, ",META_UUID");
        return s;
 }
 
diff --git a/libxfs/xfs_sb.c b/libxfs/xfs_sb.c
index c9ef019..ea30857 100644
--- a/libxfs/xfs_sb.c
+++ b/libxfs/xfs_sb.c
@@ -503,7 +503,7 @@ xfs_sb_to_disk(
         * in memory; don't write it out.
         */
        if (!xfs_sb_version_hasmetauuid(from))
-               fields &= ~XFS_SB_UUID;
+               fields &= ~XFS_SB_META_UUID;
 
        xfs_sb_quota_to_disk(to, from, &fields);
        while (fields) {
diff --git a/libxlog/util.c b/libxlog/util.c
index 949b79d..652d391 100644
--- a/libxlog/util.c
+++ b/libxlog/util.c
@@ -28,8 +28,10 @@ header_check_uuid(xfs_mount_t *mp, xlog_rec_header_t *head)
 {
     char uu_log[64], uu_sb[64];
 
-    if (print_skip_uuid) return 0;
-    if (!platform_uuid_compare(&mp->m_sb.sb_uuid, &head->h_fs_uuid)) return 0;
+    if (print_skip_uuid)
+               return 0;
+    if (!platform_uuid_compare(&mp->m_sb.sb_uuid, &head->h_fs_uuid))
+               return 0;
 
     platform_uuid_unparse(&mp->m_sb.sb_uuid, uu_sb);
     platform_uuid_unparse(&head->h_fs_uuid, uu_log);
diff --git a/man/man8/xfs_admin.8 b/man/man8/xfs_admin.8
index b393d74..0600540 100644
--- a/man/man8/xfs_admin.8
+++ b/man/man8/xfs_admin.8
@@ -98,7 +98,12 @@ The
 .I uuid
 may also be
 .BR generate ,
-which will generate a new UUID for the filesystem.
+which will generate a new UUID for the filesystem.  Note that on CRC-enabled
+filesystems, this will set an incompatible flag such that older kernels will
+not be able to mount the filesystem.  To remove this incompatible flag, use
+.BR restore ,
+which will match the UUID to the metadata UUID and remove the incompatible
+feature flag.
 .TP
 .B \-V
 Prints the version number and exits.
diff --git a/man/man8/xfs_db.8 b/man/man8/xfs_db.8
index d527230..7c471aa 100644
--- a/man/man8/xfs_db.8
+++ b/man/man8/xfs_db.8
@@ -664,7 +664,7 @@ The possible data types are:
 .BR sb ", " symlink " and " text .
 See the TYPES section below for more information on these data types.
 .TP
-.BI "uuid [" uuid " | " generate " | " rewrite ]
+.BI "uuid [" uuid " | " generate " | " rewrite " | " restore ]
 Set the filesystem universally unique identifier (UUID).
 The filesystem UUID can be used by
 .BR mount (8)
@@ -675,7 +675,12 @@ can be set directly to the desired UUID, or it can
 be automatically generated using the
 .B generate
 option. These options will both write the UUID into every copy of the
-superblock in the filesystem.
+superblock in the filesystem.  On a CRC-enabled filesystem, this will
+set an incompatible superblock flag, and the filesystem will not be
+mountable with older kernels.  This can be reverted with the
+.B restore
+option, which will copy the original UUID back into place, and clear
+the incompatible flag.
 .B rewrite
 copies the current UUID from the primary superblock
 to all secondary copies of the superblock.
diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
index 5084d75..eb8b74d 100644
--- a/mkfs/xfs_mkfs.c
+++ b/mkfs/xfs_mkfs.c
@@ -2598,6 +2598,8 @@ _("size %s specified for log subvolume is too large, 
maximum is %lld blocks\n"),
        sbp->sb_rextents = rtextents;
        platform_uuid_generate(&uuid);
        platform_uuid_copy(&sbp->sb_uuid, &uuid);
+       /* Only in memory; libxfs expects this */
+       platform_uuid_copy(&sbp->sb_meta_uuid, &uuid);
        sbp->sb_logstart = logstart;
        sbp->sb_rootino = sbp->sb_rbmino = sbp->sb_rsumino = NULLFSINO;
        sbp->sb_rextsize = rtextblocks;
diff --git a/repair/agheader.c b/repair/agheader.c
index 5dbf992..5200ff0 100644
--- a/repair/agheader.c
+++ b/repair/agheader.c
@@ -112,7 +112,7 @@ verify_set_agf(xfs_mount_t *mp, xfs_agf_t *agf, 
xfs_agnumber_t i)
        if (!xfs_sb_version_hascrc(&mp->m_sb))
                return retval;
 
-       if (platform_uuid_compare(&agf->agf_uuid, &mp->m_sb.sb_uuid)) {
+       if (platform_uuid_compare(&agf->agf_uuid, &mp->m_sb.sb_meta_uuid)) {
                char uu[64];
 
                retval = XR_AG_AGF;
@@ -120,7 +120,8 @@ verify_set_agf(xfs_mount_t *mp, xfs_agf_t *agf, 
xfs_agnumber_t i)
                do_warn(_("bad uuid %s for agf %d\n"), uu, i);
 
                if (!no_modify)
-                       platform_uuid_copy(&agf->agf_uuid, &mp->m_sb.sb_uuid);
+                       platform_uuid_copy(&agf->agf_uuid,
+                                          &mp->m_sb.sb_meta_uuid);
        }
        return retval;
 }
@@ -190,7 +191,7 @@ verify_set_agi(xfs_mount_t *mp, xfs_agi_t *agi, 
xfs_agnumber_t agno)
        if (!xfs_sb_version_hascrc(&mp->m_sb))
                return retval;
 
-       if (platform_uuid_compare(&agi->agi_uuid, &mp->m_sb.sb_uuid)) {
+       if (platform_uuid_compare(&agi->agi_uuid, &mp->m_sb.sb_meta_uuid)) {
                char uu[64];
 
                retval = XR_AG_AGI;
@@ -198,7 +199,8 @@ verify_set_agi(xfs_mount_t *mp, xfs_agi_t *agi, 
xfs_agnumber_t agno)
                do_warn(_("bad uuid %s for agi %d\n"), uu, agno);
 
                if (!no_modify)
-                       platform_uuid_copy(&agi->agi_uuid, &mp->m_sb.sb_uuid);
+                       platform_uuid_copy(&agi->agi_uuid,
+                                          &mp->m_sb.sb_meta_uuid);
        }
 
        return retval;
@@ -245,7 +247,7 @@ compare_sb(xfs_mount_t *mp, xfs_sb_t *sb)
  * superblocks, not just the secondary superblocks.
  */
 static int
-secondary_sb_wack(
+secondary_sb_whack(
        struct xfs_mount *mp,
        struct xfs_buf  *sbuf,
        struct xfs_sb   *sb,
@@ -267,7 +269,10 @@ secondary_sb_wack(
         *
         * size is the size of data which is valid for this sb.
         */
-       if (xfs_sb_version_hascrc(sb))
+       if (xfs_sb_version_hasmetauuid(sb))
+               size = offsetof(xfs_sb_t, sb_meta_uuid)
+                       + sizeof(sb->sb_meta_uuid);
+       else if (xfs_sb_version_hascrc(sb))
                size = offsetof(xfs_sb_t, sb_lsn)
                        + sizeof(sb->sb_lsn);
        else if (xfs_sb_version_hasmorebits(sb))
@@ -526,7 +531,7 @@ verify_set_agheader(xfs_mount_t *mp, xfs_buf_t *sbuf, 
xfs_sb_t *sb,
                rval |= XR_AG_SB;
        }
 
-       rval |= secondary_sb_wack(mp, sbuf, sb, i);
+       rval |= secondary_sb_whack(mp, sbuf, sb, i);
 
        rval |= verify_set_agf(mp, agf, i);
        rval |= verify_set_agi(mp, agi, i);
diff --git a/repair/agheader.h b/repair/agheader.h
index b5c10ec..fa6fc26 100644
--- a/repair/agheader.h
+++ b/repair/agheader.h
@@ -24,7 +24,6 @@ typedef struct fs_geometry  {
        xfs_drfsbno_t   sb_dblocks;     /* # data blocks */
        xfs_drfsbno_t   sb_rblocks;     /* # realtime blocks */
        xfs_drtbno_t    sb_rextents;    /* # realtime extents */
-       uuid_t          sb_uuid;        /* fs uuid */
        xfs_dfsbno_t    sb_logstart;    /* starting log block # */
        xfs_agblock_t   sb_rextsize;    /* realtime extent size (blocks )*/
        xfs_agblock_t   sb_agblocks;    /* # of blocks per ag */
diff --git a/repair/dinode.c b/repair/dinode.c
index 035212c..5d22652 100644
--- a/repair/dinode.c
+++ b/repair/dinode.c
@@ -208,9 +208,9 @@ clear_dinode_core(struct xfs_mount *mp, xfs_dinode_t 
*dinoc, xfs_ino_t ino_num)
                dinoc->di_ino = cpu_to_be64(ino_num);
        }
 
-       if (platform_uuid_compare(&dinoc->di_uuid, &mp->m_sb.sb_uuid)) {
+       if (platform_uuid_compare(&dinoc->di_uuid, &mp->m_sb.sb_meta_uuid)) {
                __dirty_no_modify_ret(dirty);
-               platform_uuid_copy(&dinoc->di_uuid, &mp->m_sb.sb_uuid);
+               platform_uuid_copy(&dinoc->di_uuid, &mp->m_sb.sb_meta_uuid);
        }
 
        for (i = 0; i < sizeof(dinoc->di_pad2)/sizeof(dinoc->di_pad2[0]); i++) {
@@ -2366,7 +2366,8 @@ _("inode identifier %llu mismatch on inode %" PRIu64 
"\n"),
                                return 1;
                        goto clear_bad_out;
                }
-               if (platform_uuid_compare(&dino->di_uuid, &mp->m_sb.sb_uuid)) {
+               if (platform_uuid_compare(&dino->di_uuid,
+                                         &mp->m_sb.sb_meta_uuid)) {
                        if (!uncertain)
                                do_warn(
                        _("UUID mismatch on inode %" PRIu64 "\n"), lino);
diff --git a/repair/phase5.c b/repair/phase5.c
index 3a2cdbb..d6f2ead 100644
--- a/repair/phase5.c
+++ b/repair/phase5.c
@@ -1119,7 +1119,7 @@ build_agi(xfs_mount_t *mp, xfs_agnumber_t agno, 
bt_status_t *btree_curs,
                agi->agi_unlinked[i] = cpu_to_be32(NULLAGINO);
 
        if (xfs_sb_version_hascrc(&mp->m_sb))
-               platform_uuid_copy(&agi->agi_uuid, &mp->m_sb.sb_uuid);
+               platform_uuid_copy(&agi->agi_uuid, &mp->m_sb.sb_meta_uuid);
 
        if (xfs_sb_version_hasfinobt(&mp->m_sb)) {
                agi->agi_free_root = cpu_to_be32(finobt_curs->root);
@@ -1360,7 +1360,7 @@ build_agf_agfl(xfs_mount_t        *mp,
 #endif
 
        if (xfs_sb_version_hascrc(&mp->m_sb))
-               platform_uuid_copy(&agf->agf_uuid, &mp->m_sb.sb_uuid);
+               platform_uuid_copy(&agf->agf_uuid, &mp->m_sb.sb_meta_uuid);
 
        /* initialise the AGFL, then fill it if there are blocks left over. */
        agfl_buf = libxfs_getbuf(mp->m_dev,
@@ -1374,7 +1374,7 @@ build_agf_agfl(xfs_mount_t        *mp,
        if (xfs_sb_version_hascrc(&mp->m_sb)) {
                agfl->agfl_magicnum = cpu_to_be32(XFS_AGFL_MAGIC);
                agfl->agfl_seqno = cpu_to_be32(agno);
-               platform_uuid_copy(&agfl->agfl_uuid, &mp->m_sb.sb_uuid);
+               platform_uuid_copy(&agfl->agfl_uuid, &mp->m_sb.sb_meta_uuid);
                for (i = 0; i < XFS_AGFL_SIZE(mp); i++)
                        agfl->agfl_bno[i] = cpu_to_be32(NULLAGBLOCK);
        }
diff --git a/repair/phase6.c b/repair/phase6.c
index c09b394..96204b9 100644
--- a/repair/phase6.c
+++ b/repair/phase6.c
@@ -526,7 +526,7 @@ mk_rbmino(xfs_mount_t *mp)
                ip->i_d.di_flags2 = 0;
                ip->i_d.di_ino = mp->m_sb.sb_rbmino;
                memset(&(ip->i_d.di_pad2[0]), 0, sizeof(ip->i_d.di_pad2));
-               platform_uuid_copy(&ip->i_d.di_uuid, &mp->m_sb.sb_uuid);
+               platform_uuid_copy(&ip->i_d.di_uuid, &mp->m_sb.sb_meta_uuid);
                times |= XFS_ICHGTIME_CREATE;
        }
        libxfs_trans_ichgtime(tp, ip, times);
@@ -782,7 +782,7 @@ mk_rsumino(xfs_mount_t *mp)
                ip->i_d.di_flags2 = 0;
                ip->i_d.di_ino = mp->m_sb.sb_rsumino;
                memset(&(ip->i_d.di_pad2[0]), 0, sizeof(ip->i_d.di_pad2));
-               platform_uuid_copy(&ip->i_d.di_uuid, &mp->m_sb.sb_uuid);
+               platform_uuid_copy(&ip->i_d.di_uuid, &mp->m_sb.sb_meta_uuid);
                times |= XFS_ICHGTIME_CREATE;
        }
        libxfs_trans_ichgtime(tp, ip, times);
@@ -898,7 +898,7 @@ mk_root_dir(xfs_mount_t *mp)
                ip->i_d.di_flags2 = 0;
                ip->i_d.di_ino = mp->m_sb.sb_rootino;
                memset(&(ip->i_d.di_pad2[0]), 0, sizeof(ip->i_d.di_pad2));
-               platform_uuid_copy(&ip->i_d.di_uuid, &mp->m_sb.sb_uuid);
+               platform_uuid_copy(&ip->i_d.di_uuid, &mp->m_sb.sb_meta_uuid);
                times |= XFS_ICHGTIME_CREATE;
        }
        libxfs_trans_ichgtime(tp, ip, times);


diff --git a/include/xfs_sb.h b/include/xfs_sb.h
index 950d1ea..c27c294 100644
--- a/include/xfs_sb.h
+++ b/include/xfs_sb.h
@@ -107,7 +107,7 @@ typedef struct xfs_sb {
        xfs_drfsbno_t   sb_dblocks;     /* number of data blocks */
        xfs_drfsbno_t   sb_rblocks;     /* number of realtime blocks */
        xfs_drtbno_t    sb_rextents;    /* number of realtime extents */
-       uuid_t          sb_uuid;        /* file system unique id */
+       uuid_t          sb_uuid;        /* user-visible file system unique id */
        xfs_dfsbno_t    sb_logstart;    /* starting block of log if internal */
        xfs_ino_t       sb_rootino;     /* root inode number */
        xfs_ino_t       sb_rbmino;      /* bitmap inode for realtime extents */
@@ -178,6 +178,7 @@ typedef struct xfs_sb {
 
        xfs_ino_t       sb_pquotino;    /* project quota inode */
        xfs_lsn_t       sb_lsn;         /* last write sequence */
+       uuid_t          sb_meta_uuid;   /* metadata file system unique id */
 
        /* must be padded to 64 bit alignment */
 } xfs_sb_t;
@@ -194,7 +195,7 @@ typedef struct xfs_dsb {
        __be64          sb_dblocks;     /* number of data blocks */
        __be64          sb_rblocks;     /* number of realtime blocks */
        __be64          sb_rextents;    /* number of realtime extents */
-       uuid_t          sb_uuid;        /* file system unique id */
+       uuid_t          sb_uuid;        /* user-visible file system unique id */
        __be64          sb_logstart;    /* starting block of log if internal */
        __be64          sb_rootino;     /* root inode number */
        __be64          sb_rbmino;      /* bitmap inode for realtime extents */
@@ -264,6 +265,7 @@ typedef struct xfs_dsb {
 
        __be64          sb_pquotino;    /* project quota inode */
        __be64          sb_lsn;         /* last write sequence */
+       uuid_t          sb_meta_uuid;   /* metadata file system unique id */
 
        /* must be padded to 64 bit alignment */
 } xfs_dsb_t;
@@ -287,7 +289,7 @@ typedef enum {
        XFS_SBS_FEATURES2, XFS_SBS_BAD_FEATURES2, XFS_SBS_FEATURES_COMPAT,
        XFS_SBS_FEATURES_RO_COMPAT, XFS_SBS_FEATURES_INCOMPAT,
        XFS_SBS_FEATURES_LOG_INCOMPAT, XFS_SBS_CRC, XFS_SBS_PAD,
-       XFS_SBS_PQUOTINO, XFS_SBS_LSN,
+       XFS_SBS_PQUOTINO, XFS_SBS_LSN, XFS_SBS_META_UUID,
        XFS_SBS_FIELDCOUNT
 } xfs_sb_field_t;
 
@@ -319,6 +321,7 @@ typedef enum {
 #define XFS_SB_FEATURES_LOG_INCOMPAT XFS_SB_MVAL(FEATURES_LOG_INCOMPAT)
 #define XFS_SB_CRC             XFS_SB_MVAL(CRC)
 #define XFS_SB_PQUOTINO                XFS_SB_MVAL(PQUOTINO)
+#define        XFS_SB_META_UUID        XFS_SB_MVAL(META_UUID)
 #define        XFS_SB_NUM_BITS         ((int)XFS_SBS_FIELDCOUNT)
 #define        XFS_SB_ALL_BITS         ((1LL << XFS_SB_NUM_BITS) - 1)
 #define        XFS_SB_MOD_BITS         \
@@ -328,7 +331,7 @@ typedef enum {
         XFS_SB_ICOUNT | XFS_SB_IFREE | XFS_SB_FDBLOCKS | XFS_SB_FEATURES2 | \
         XFS_SB_BAD_FEATURES2 | XFS_SB_FEATURES_COMPAT | \
         XFS_SB_FEATURES_RO_COMPAT | XFS_SB_FEATURES_INCOMPAT | \
-        XFS_SB_FEATURES_LOG_INCOMPAT | XFS_SB_PQUOTINO)
+        XFS_SB_FEATURES_LOG_INCOMPAT | XFS_SB_PQUOTINO | XFS_SB_META_UUID)
 
 
 /*
@@ -600,8 +603,10 @@ xfs_sb_has_ro_compat_feature(
 }
 
 #define XFS_SB_FEAT_INCOMPAT_FTYPE     (1 << 0)        /* filetype in dirent */
+#define XFS_SB_FEAT_INCOMPAT_META_UUID (1 << 1)                /* metadata 
UUID */
 #define XFS_SB_FEAT_INCOMPAT_ALL \
-               (XFS_SB_FEAT_INCOMPAT_FTYPE)
+               (XFS_SB_FEAT_INCOMPAT_FTYPE | \
+                XFS_SB_FEAT_INCOMPAT_META_UUID)
 
 #define XFS_SB_FEAT_INCOMPAT_UNKNOWN   ~XFS_SB_FEAT_INCOMPAT_ALL
 static inline bool
@@ -650,6 +655,18 @@ static inline int xfs_sb_version_hasfinobt(xfs_sb_t *sbp)
 }
 
 /*
+ * XFS_SB_FEAT_INCOMPAT_META_UUID indicates that the metadata UUID
+ * is stored separately from the user-visible UUID; this allows the
+ * user-visible UUID to be changed on V5 filesystems which have a
+ * filesystem UUID stamped into every piece of metadata.
+ */
+static inline int xfs_sb_version_hasmetauuid(xfs_sb_t *sbp)
+{
+       return (XFS_SB_VERSION_NUM(sbp) == XFS_SB_VERSION_5) &&
+               (sbp->sb_features_incompat & XFS_SB_FEAT_INCOMPAT_META_UUID);
+}
+
+/*
  * end of superblock version macros
  */
 
diff --git a/libxfs/util.c b/libxfs/util.c
index 49eb76d..ea698c4 100644
--- a/libxfs/util.c
+++ b/libxfs/util.c
@@ -250,7 +250,7 @@ libxfs_ialloc(
 
        if (ip->i_d.di_version == 3) {
                ASSERT(ip->i_d.di_ino == ino);
-               ASSERT(uuid_equal(&ip->i_d.di_uuid, &mp->m_sb.sb_uuid));
+               ASSERT(uuid_equal(&ip->i_d.di_uuid, &mp->m_sb.sb_meta_uuid));
                ip->i_d.di_crc = 0;
                ip->i_d.di_changecount = 1;
                ip->i_d.di_lsn = 0;
diff --git a/libxfs/xfs_alloc.c b/libxfs/xfs_alloc.c
index 6c82be0..06757c3 100644
--- a/libxfs/xfs_alloc.c
+++ b/libxfs/xfs_alloc.c
@@ -426,7 +426,7 @@ xfs_agfl_verify(
        struct xfs_agfl *agfl = XFS_BUF_TO_AGFL(bp);
        int             i;
 
-       if (!uuid_equal(&agfl->agfl_uuid, &mp->m_sb.sb_uuid))
+       if (!uuid_equal(&agfl->agfl_uuid, &mp->m_sb.sb_meta_uuid))
                return false;
        if (be32_to_cpu(agfl->agfl_magicnum) != XFS_AGFL_MAGIC)
                return false;
@@ -2181,7 +2181,7 @@ xfs_agf_verify(
        struct xfs_agf  *agf = XFS_BUF_TO_AGF(bp);
 
        if (xfs_sb_version_hascrc(&mp->m_sb) &&
-           !uuid_equal(&agf->agf_uuid, &mp->m_sb.sb_uuid))
+           !uuid_equal(&agf->agf_uuid, &mp->m_sb.sb_meta_uuid))
                        return false;
 
        if (!(agf->agf_magicnum == cpu_to_be32(XFS_AGF_MAGIC) &&
diff --git a/libxfs/xfs_alloc_btree.c b/libxfs/xfs_alloc_btree.c
index 215be7e..cefa18b 100644
--- a/libxfs/xfs_alloc_btree.c
+++ b/libxfs/xfs_alloc_btree.c
@@ -279,7 +279,7 @@ xfs_allocbt_verify(
        case cpu_to_be32(XFS_ABTB_CRC_MAGIC):
                if (!xfs_sb_version_hascrc(&mp->m_sb))
                        return false;
-               if (!uuid_equal(&block->bb_u.s.bb_uuid, &mp->m_sb.sb_uuid))
+               if (!uuid_equal(&block->bb_u.s.bb_uuid, &mp->m_sb.sb_meta_uuid))
                        return false;
                if (block->bb_u.s.bb_blkno != cpu_to_be64(bp->b_bn))
                        return false;
@@ -297,7 +297,7 @@ xfs_allocbt_verify(
        case cpu_to_be32(XFS_ABTC_CRC_MAGIC):
                if (!xfs_sb_version_hascrc(&mp->m_sb))
                        return false;
-               if (!uuid_equal(&block->bb_u.s.bb_uuid, &mp->m_sb.sb_uuid))
+               if (!uuid_equal(&block->bb_u.s.bb_uuid, &mp->m_sb.sb_meta_uuid))
                        return false;
                if (block->bb_u.s.bb_blkno != cpu_to_be64(bp->b_bn))
                        return false;
diff --git a/libxfs/xfs_attr_leaf.c b/libxfs/xfs_attr_leaf.c
index f7f02ae..e9f96ec 100644
--- a/libxfs/xfs_attr_leaf.c
+++ b/libxfs/xfs_attr_leaf.c
@@ -161,7 +161,7 @@ xfs_attr3_leaf_verify(
                if (ichdr.magic != XFS_ATTR3_LEAF_MAGIC)
                        return false;
 
-               if (!uuid_equal(&hdr3->info.uuid, &mp->m_sb.sb_uuid))
+               if (!uuid_equal(&hdr3->info.uuid, &mp->m_sb.sb_meta_uuid))
                        return false;
                if (be64_to_cpu(hdr3->info.blkno) != bp->b_bn)
                        return false;
@@ -952,7 +952,7 @@ xfs_attr3_leaf_create(
 
                hdr3->blkno = cpu_to_be64(bp->b_bn);
                hdr3->owner = cpu_to_be64(dp->i_ino);
-               uuid_copy(&hdr3->uuid, &mp->m_sb.sb_uuid);
+               uuid_copy(&hdr3->uuid, &mp->m_sb.sb_meta_uuid);
 
                ichdr.freemap[0].base = sizeof(struct xfs_attr3_leaf_hdr);
        } else {
diff --git a/libxfs/xfs_attr_remote.c b/libxfs/xfs_attr_remote.c
index 08b983b..62abaec 100644
--- a/libxfs/xfs_attr_remote.c
+++ b/libxfs/xfs_attr_remote.c
@@ -78,7 +78,7 @@ xfs_attr3_rmt_verify(
                return false;
        if (rmt->rm_magic != cpu_to_be32(XFS_ATTR3_RMT_MAGIC))
                return false;
-       if (!uuid_equal(&rmt->rm_uuid, &mp->m_sb.sb_uuid))
+       if (!uuid_equal(&rmt->rm_uuid, &mp->m_sb.sb_meta_uuid))
                return false;
        if (be64_to_cpu(rmt->rm_blkno) != bno)
                return false;
@@ -194,7 +194,7 @@ xfs_attr3_rmt_hdr_set(
        rmt->rm_magic = cpu_to_be32(XFS_ATTR3_RMT_MAGIC);
        rmt->rm_offset = cpu_to_be32(offset);
        rmt->rm_bytes = cpu_to_be32(size);
-       uuid_copy(&rmt->rm_uuid, &mp->m_sb.sb_uuid);
+       uuid_copy(&rmt->rm_uuid, &mp->m_sb.sb_meta_uuid);
        rmt->rm_owner = cpu_to_be64(ino);
        rmt->rm_blkno = cpu_to_be64(bno);
 
diff --git a/libxfs/xfs_bmap_btree.c b/libxfs/xfs_bmap_btree.c
index a4bd69d..9913958 100644
--- a/libxfs/xfs_bmap_btree.c
+++ b/libxfs/xfs_bmap_btree.c
@@ -412,7 +412,8 @@ xfs_bmbt_to_bmdr(
 
        if (xfs_sb_version_hascrc(&mp->m_sb)) {
                ASSERT(rblock->bb_magic == cpu_to_be32(XFS_BMAP_CRC_MAGIC));
-               ASSERT(uuid_equal(&rblock->bb_u.l.bb_uuid, &mp->m_sb.sb_uuid));
+               ASSERT(uuid_equal(&rblock->bb_u.l.bb_uuid,
+                                 &mp->m_sb.sb_meta_uuid));
                ASSERT(rblock->bb_u.l.bb_blkno ==
                       cpu_to_be64(XFS_BUF_DADDR_NULL));
        } else
@@ -712,7 +713,7 @@ xfs_bmbt_verify(
        case cpu_to_be32(XFS_BMAP_CRC_MAGIC):
                if (!xfs_sb_version_hascrc(&mp->m_sb))
                        return false;
-               if (!uuid_equal(&block->bb_u.l.bb_uuid, &mp->m_sb.sb_uuid))
+               if (!uuid_equal(&block->bb_u.l.bb_uuid, &mp->m_sb.sb_meta_uuid))
                        return false;
                if (be64_to_cpu(block->bb_u.l.bb_blkno) != bp->b_bn)
                        return false;
diff --git a/libxfs/xfs_btree.c b/libxfs/xfs_btree.c
index cc823f5..a8436f5 100644
--- a/libxfs/xfs_btree.c
+++ b/libxfs/xfs_btree.c
@@ -50,7 +50,8 @@ xfs_btree_check_lblock(
 
        if (xfs_sb_version_hascrc(&mp->m_sb)) {
                lblock_ok = lblock_ok &&
-                       uuid_equal(&block->bb_u.l.bb_uuid, &mp->m_sb.sb_uuid) &&
+                       uuid_equal(&block->bb_u.l.bb_uuid,
+                                  &mp->m_sb.sb_meta_uuid) &&
                        block->bb_u.l.bb_blkno == cpu_to_be64(
                                bp ? bp->b_bn : XFS_BUF_DADDR_NULL);
        }
@@ -100,7 +101,8 @@ xfs_btree_check_sblock(
 
        if (xfs_sb_version_hascrc(&mp->m_sb)) {
                sblock_ok = sblock_ok &&
-                       uuid_equal(&block->bb_u.s.bb_uuid, &mp->m_sb.sb_uuid) &&
+                       uuid_equal(&block->bb_u.s.bb_uuid,
+                                  &mp->m_sb.sb_meta_uuid) &&
                        block->bb_u.s.bb_blkno == cpu_to_be64(
                                bp ? bp->b_bn : XFS_BUF_DADDR_NULL);
        }
@@ -992,7 +994,7 @@ xfs_btree_init_block_int(
                if (flags & XFS_BTREE_CRC_BLOCKS) {
                        buf->bb_u.l.bb_blkno = cpu_to_be64(blkno);
                        buf->bb_u.l.bb_owner = cpu_to_be64(owner);
-                       uuid_copy(&buf->bb_u.l.bb_uuid, &mp->m_sb.sb_uuid);
+                       uuid_copy(&buf->bb_u.l.bb_uuid, &mp->m_sb.sb_meta_uuid);
                        buf->bb_u.l.bb_pad = 0;
                        buf->bb_u.l.bb_lsn = 0;
                }
@@ -1005,7 +1007,7 @@ xfs_btree_init_block_int(
                if (flags & XFS_BTREE_CRC_BLOCKS) {
                        buf->bb_u.s.bb_blkno = cpu_to_be64(blkno);
                        buf->bb_u.s.bb_owner = cpu_to_be32(__owner);
-                       uuid_copy(&buf->bb_u.s.bb_uuid, &mp->m_sb.sb_uuid);
+                       uuid_copy(&buf->bb_u.s.bb_uuid, &mp->m_sb.sb_meta_uuid);
                        buf->bb_u.s.bb_lsn = 0;
                }
        }
diff --git a/libxfs/xfs_da_btree.c b/libxfs/xfs_da_btree.c
index b731b54..0323dc7 100644
--- a/libxfs/xfs_da_btree.c
+++ b/libxfs/xfs_da_btree.c
@@ -172,7 +172,7 @@ xfs_da3_node_verify(
                if (ichdr.magic != XFS_DA3_NODE_MAGIC)
                        return false;
 
-               if (!uuid_equal(&hdr3->info.uuid, &mp->m_sb.sb_uuid))
+               if (!uuid_equal(&hdr3->info.uuid, &mp->m_sb.sb_meta_uuid))
                        return false;
                if (be64_to_cpu(hdr3->info.blkno) != bp->b_bn)
                        return false;
@@ -349,7 +349,7 @@ xfs_da3_node_create(
                ichdr.magic = XFS_DA3_NODE_MAGIC;
                hdr3->info.blkno = cpu_to_be64(bp->b_bn);
                hdr3->info.owner = cpu_to_be64(args->dp->i_ino);
-               uuid_copy(&hdr3->info.uuid, &mp->m_sb.sb_uuid);
+               uuid_copy(&hdr3->info.uuid, &mp->m_sb.sb_meta_uuid);
        } else {
                ichdr.magic = XFS_DA_NODE_MAGIC;
        }
diff --git a/libxfs/xfs_dir2_block.c b/libxfs/xfs_dir2_block.c
index cede01f..2a25059 100644
--- a/libxfs/xfs_dir2_block.c
+++ b/libxfs/xfs_dir2_block.c
@@ -51,7 +51,7 @@ xfs_dir3_block_verify(
        if (xfs_sb_version_hascrc(&mp->m_sb)) {
                if (hdr3->magic != cpu_to_be32(XFS_DIR3_BLOCK_MAGIC))
                        return false;
-               if (!uuid_equal(&hdr3->uuid, &mp->m_sb.sb_uuid))
+               if (!uuid_equal(&hdr3->uuid, &mp->m_sb.sb_meta_uuid))
                        return false;
                if (be64_to_cpu(hdr3->blkno) != bp->b_bn)
                        return false;
@@ -141,7 +141,7 @@ xfs_dir3_block_init(
                hdr3->magic = cpu_to_be32(XFS_DIR3_BLOCK_MAGIC);
                hdr3->blkno = cpu_to_be64(bp->b_bn);
                hdr3->owner = cpu_to_be64(dp->i_ino);
-               uuid_copy(&hdr3->uuid, &mp->m_sb.sb_uuid);
+               uuid_copy(&hdr3->uuid, &mp->m_sb.sb_meta_uuid);
                return;
 
        }
diff --git a/libxfs/xfs_dir2_data.c b/libxfs/xfs_dir2_data.c
index dc9df4d..4c79d7c 100644
--- a/libxfs/xfs_dir2_data.c
+++ b/libxfs/xfs_dir2_data.c
@@ -186,7 +186,7 @@ xfs_dir3_data_verify(
        if (xfs_sb_version_hascrc(&mp->m_sb)) {
                if (hdr3->magic != cpu_to_be32(XFS_DIR3_DATA_MAGIC))
                        return false;
-               if (!uuid_equal(&hdr3->uuid, &mp->m_sb.sb_uuid))
+               if (!uuid_equal(&hdr3->uuid, &mp->m_sb.sb_meta_uuid))
                        return false;
                if (be64_to_cpu(hdr3->blkno) != bp->b_bn)
                        return false;
@@ -573,7 +573,7 @@ xfs_dir3_data_init(
                hdr3->magic = cpu_to_be32(XFS_DIR3_DATA_MAGIC);
                hdr3->blkno = cpu_to_be64(bp->b_bn);
                hdr3->owner = cpu_to_be64(dp->i_ino);
-               uuid_copy(&hdr3->uuid, &mp->m_sb.sb_uuid);
+               uuid_copy(&hdr3->uuid, &mp->m_sb.sb_meta_uuid);
 
        } else
                hdr->magic = cpu_to_be32(XFS_DIR2_DATA_MAGIC);
diff --git a/libxfs/xfs_dir2_leaf.c b/libxfs/xfs_dir2_leaf.c
index 8e0cbc9..a918e15 100644
--- a/libxfs/xfs_dir2_leaf.c
+++ b/libxfs/xfs_dir2_leaf.c
@@ -186,7 +186,7 @@ xfs_dir3_leaf_verify(
 
                if (leaf3->info.hdr.magic != cpu_to_be16(magic3))
                        return false;
-               if (!uuid_equal(&leaf3->info.uuid, &mp->m_sb.sb_uuid))
+               if (!uuid_equal(&leaf3->info.uuid, &mp->m_sb.sb_meta_uuid))
                        return false;
                if (be64_to_cpu(leaf3->info.blkno) != bp->b_bn)
                        return false;
@@ -337,7 +337,7 @@ xfs_dir3_leaf_init(
                                         : cpu_to_be16(XFS_DIR3_LEAFN_MAGIC);
                leaf3->info.blkno = cpu_to_be64(bp->b_bn);
                leaf3->info.owner = cpu_to_be64(owner);
-               uuid_copy(&leaf3->info.uuid, &mp->m_sb.sb_uuid);
+               uuid_copy(&leaf3->info.uuid, &mp->m_sb.sb_meta_uuid);
        } else {
                memset(leaf, 0, sizeof(*leaf));
                leaf->hdr.info.magic = cpu_to_be16(type);
diff --git a/libxfs/xfs_dir2_node.c b/libxfs/xfs_dir2_node.c
index 3737e4e..309e7ce 100644
--- a/libxfs/xfs_dir2_node.c
+++ b/libxfs/xfs_dir2_node.c
@@ -78,7 +78,7 @@ xfs_dir3_free_verify(
 
                if (hdr3->magic != cpu_to_be32(XFS_DIR3_FREE_MAGIC))
                        return false;
-               if (!uuid_equal(&hdr3->uuid, &mp->m_sb.sb_uuid))
+               if (!uuid_equal(&hdr3->uuid, &mp->m_sb.sb_meta_uuid))
                        return false;
                if (be64_to_cpu(hdr3->blkno) != bp->b_bn)
                        return false;
@@ -257,7 +257,7 @@ xfs_dir3_free_get_buf(
 
                hdr3->hdr.blkno = cpu_to_be64(bp->b_bn);
                hdr3->hdr.owner = cpu_to_be64(dp->i_ino);
-               uuid_copy(&hdr3->hdr.uuid, &mp->m_sb.sb_uuid);
+               uuid_copy(&hdr3->hdr.uuid, &mp->m_sb.sb_meta_uuid);
        } else
                hdr.magic = XFS_DIR2_FREE_MAGIC;
        xfs_dir3_free_hdr_to_disk(bp->b_addr, &hdr);
diff --git a/libxfs/xfs_dquot_buf.c b/libxfs/xfs_dquot_buf.c
index e089ec8..f75bfe3 100644
--- a/libxfs/xfs_dquot_buf.c
+++ b/libxfs/xfs_dquot_buf.c
@@ -146,7 +146,7 @@ xfs_dqcheck(
        d->dd_diskdq.d_id = cpu_to_be32(id);
 
        if (xfs_sb_version_hascrc(&mp->m_sb)) {
-               uuid_copy(&d->dd_uuid, &mp->m_sb.sb_uuid);
+               uuid_copy(&d->dd_uuid, &mp->m_sb.sb_meta_uuid);
                xfs_update_cksum((char *)d, sizeof(struct xfs_dqblk),
                                 XFS_DQUOT_CRC_OFF);
        }
@@ -181,7 +181,7 @@ xfs_dquot_buf_verify_crc(
                if (!xfs_verify_cksum((char *)d, sizeof(struct xfs_dqblk),
                                 XFS_DQUOT_CRC_OFF))
                        return false;
-               if (!uuid_equal(&d->dd_uuid, &mp->m_sb.sb_uuid))
+               if (!uuid_equal(&d->dd_uuid, &mp->m_sb.sb_meta_uuid))
                        return false;
        }
        return true;
diff --git a/libxfs/xfs_ialloc.c b/libxfs/xfs_ialloc.c
index b20a9ec..ae0804c 100644
--- a/libxfs/xfs_ialloc.c
+++ b/libxfs/xfs_ialloc.c
@@ -295,7 +295,8 @@ xfs_ialloc_inode_init(
                        if (version == 3) {
                                free->di_ino = cpu_to_be64(ino);
                                ino++;
-                               uuid_copy(&free->di_uuid, &mp->m_sb.sb_uuid);
+                               uuid_copy(&free->di_uuid,
+                                         &mp->m_sb.sb_meta_uuid);
                                xfs_dinode_calc_crc(mp, free);
                        } else if (tp) {
                                /* just log the inode core */
@@ -1947,7 +1948,7 @@ xfs_agi_verify(
        struct xfs_agi  *agi = XFS_BUF_TO_AGI(bp);
 
        if (xfs_sb_version_hascrc(&mp->m_sb) &&
-           !uuid_equal(&agi->agi_uuid, &mp->m_sb.sb_uuid))
+           !uuid_equal(&agi->agi_uuid, &mp->m_sb.sb_meta_uuid))
                        return false;
        /*
         * Validate the magic number of the agi block.
diff --git a/libxfs/xfs_ialloc_btree.c b/libxfs/xfs_ialloc_btree.c
index c337389..320984f 100644
--- a/libxfs/xfs_ialloc_btree.c
+++ b/libxfs/xfs_ialloc_btree.c
@@ -214,7 +214,7 @@ xfs_inobt_verify(
        case cpu_to_be32(XFS_FIBT_CRC_MAGIC):
                if (!xfs_sb_version_hascrc(&mp->m_sb))
                        return false;
-               if (!uuid_equal(&block->bb_u.s.bb_uuid, &mp->m_sb.sb_uuid))
+               if (!uuid_equal(&block->bb_u.s.bb_uuid, &mp->m_sb.sb_meta_uuid))
                        return false;
                if (block->bb_u.s.bb_blkno != cpu_to_be64(bp->b_bn))
                        return false;
diff --git a/libxfs/xfs_inode_buf.c b/libxfs/xfs_inode_buf.c
index de16ed9..1c0047d 100644
--- a/libxfs/xfs_inode_buf.c
+++ b/libxfs/xfs_inode_buf.c
@@ -295,7 +295,7 @@ xfs_dinode_verify(
                return false;
        if (be64_to_cpu(dip->di_ino) != ino)
                return false;
-       if (!uuid_equal(&dip->di_uuid, &mp->m_sb.sb_uuid))
+       if (!uuid_equal(&dip->di_uuid, &mp->m_sb.sb_meta_uuid))
                return false;
        return true;
 }
diff --git a/libxfs/xfs_sb.c b/libxfs/xfs_sb.c
index ea89367..c9ef019 100644
--- a/libxfs/xfs_sb.c
+++ b/libxfs/xfs_sb.c
@@ -81,6 +81,7 @@ static const struct {
        { offsetof(xfs_sb_t, sb_pad),           0 },
        { offsetof(xfs_sb_t, sb_pquotino),      0 },
        { offsetof(xfs_sb_t, sb_lsn),           0 },
+       { offsetof(xfs_sb_t, sb_meta_uuid),             1 },
        { sizeof(xfs_sb_t),                     0 }
 };
 
@@ -413,6 +414,13 @@ xfs_sb_from_disk(
        to->sb_pad = 0;
        to->sb_pquotino = be64_to_cpu(from->sb_pquotino);
        to->sb_lsn = be64_to_cpu(from->sb_lsn);
+       if (xfs_sb_version_hasmetauuid(to)) {
+               memcpy(&to->sb_meta_uuid, &from->sb_meta_uuid,
+                                       sizeof(to->sb_meta_uuid));
+       } else {
+               memcpy(&to->sb_meta_uuid, &from->sb_uuid,
+                                       sizeof(to->sb_meta_uuid));
+       }
 }
 
 static inline void
@@ -490,6 +498,13 @@ xfs_sb_to_disk(
        /* We should never write the crc here, it's updated in the IO path */
        fields &= ~XFS_SB_CRC;
 
+       /*
+        * If the metadata-specific UUID feature isn't set, it's only set
+        * in memory; don't write it out.
+        */
+       if (!xfs_sb_version_hasmetauuid(from))
+               fields &= ~XFS_SB_UUID;
+
        xfs_sb_quota_to_disk(to, from, &fields);
        while (fields) {
                f = (xfs_sb_field_t)xfs_lowbit64((__uint64_t)fields);
diff --git a/libxfs/xfs_symlink_remote.c b/libxfs/xfs_symlink_remote.c
index ebf60ac..3f8374e 100644
--- a/libxfs/xfs_symlink_remote.c
+++ b/libxfs/xfs_symlink_remote.c
@@ -48,7 +48,7 @@ xfs_symlink_hdr_set(
        dsl->sl_magic = cpu_to_be32(XFS_SYMLINK_MAGIC);
        dsl->sl_offset = cpu_to_be32(offset);
        dsl->sl_bytes = cpu_to_be32(size);
-       uuid_copy(&dsl->sl_uuid, &mp->m_sb.sb_uuid);
+       uuid_copy(&dsl->sl_uuid, &mp->m_sb.sb_meta_uuid);
        dsl->sl_owner = cpu_to_be64(ino);
        dsl->sl_blkno = cpu_to_be64(bp->b_bn);
        bp->b_ops = &xfs_symlink_buf_ops;
@@ -93,7 +93,7 @@ xfs_symlink_verify(
                return false;
        if (dsl->sl_magic != cpu_to_be32(XFS_SYMLINK_MAGIC))
                return false;
-       if (!uuid_equal(&dsl->sl_uuid, &mp->m_sb.sb_uuid))
+       if (!uuid_equal(&dsl->sl_uuid, &mp->m_sb.sb_meta_uuid))
                return false;
        if (bp->b_bn != be64_to_cpu(dsl->sl_blkno))
                return false;


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