[PATCH 3/3] xfs: sanitise sb_bad_features2 handling

Dave Chinner
2015-01-07T21:51:12Z

From: Dave Chinner <dchinner@redhat.com>

We currently have to ensure that every time we update sb_features2
that we update sb_bad_features2. Now that we log and format the
superblock in it's entirety we actually don't have to care because
we can simply update the sb_bad_features2 when we format it into the
buffer. This removes the need for anything but the mount and
superblock formatting code to care about sb_bad_features2, and
hence removes the possibility that we forget to update bad_features2
when necessary in the future.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
fs/xfs/libxfs/xfs_format.h | 14 +++++++-------
fs/xfs/libxfs/xfs_sb.c | 8 +++++++-
fs/xfs/xfs_mount.c | 23 +++++++++++------------
3 files changed, 25 insertions(+), 20 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
index 4762732..8eb7189 100644
--- a/fs/xfs/libxfs/xfs_format.h
+++ b/fs/xfs/libxfs/xfs_format.h
@@ -151,10 +151,13 @@ typedef struct xfs_sb {
__uint32_t sb_features2; /* additional feature bits */

/*
- * bad features2 field as a result of failing to pad the sb
- * structure to 64 bits. Some machines will be using this field
- * for features2 bits. Easiest just to mark it bad and not use
- * it for anything else.
+ * bad features2 field as a result of failing to pad the sb structure to
+ * 64 bits. Some machines will be using this field for features2 bits.
+ * Easiest just to mark it bad and not use it for anything else.
+ *
+ * This is not kept up to date in memory; it is always overwritten by
+ * the value in sb_features2 when formatting the incore superblock to
+ * the disk buffer.
*/
__uint32_t sb_bad_features2;

@@ -453,13 +456,11 @@ static inline void xfs_sb_version_addattr2(struct xfs_sb *sbp)
{
sbp->sb_versionnum |= XFS_SB_VERSION_MOREBITSBIT;
sbp->sb_features2 |= XFS_SB_VERSION2_ATTR2BIT;
- sbp->sb_bad_features2 |= XFS_SB_VERSION2_ATTR2BIT;
}

static inline void xfs_sb_version_removeattr2(struct xfs_sb *sbp)
{
sbp->sb_features2 &= ~XFS_SB_VERSION2_ATTR2BIT;
- sbp->sb_bad_features2 &= ~XFS_SB_VERSION2_ATTR2BIT;
if (!sbp->sb_features2)
sbp->sb_versionnum &= ~XFS_SB_VERSION_MOREBITSBIT;
}
@@ -475,7 +476,6 @@ static inline void xfs_sb_version_addprojid32bit(struct xfs_sb *sbp)
{
sbp->sb_versionnum |= XFS_SB_VERSION_MOREBITSBIT;
sbp->sb_features2 |= XFS_SB_VERSION2_PROJID32BIT;
- sbp->sb_bad_features2 |= XFS_SB_VERSION2_PROJID32BIT;
}

/*
diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
index 6ee3af6..b440839 100644
--- a/fs/xfs/libxfs/xfs_sb.c
+++ b/fs/xfs/libxfs/xfs_sb.c
@@ -488,7 +488,6 @@ xfs_sb_to_disk(
to->sb_fdblocks = cpu_to_be64(from->sb_fdblocks);
to->sb_frextents = cpu_to_be64(from->sb_frextents);

-
to->sb_flags = from->sb_flags;
to->sb_shared_vn = from->sb_shared_vn;
to->sb_inoalignmt = cpu_to_be32(from->sb_inoalignmt);
@@ -498,6 +497,13 @@ xfs_sb_to_disk(
to->sb_logsectlog = from->sb_logsectlog;
to->sb_logsectsize = cpu_to_be16(from->sb_logsectsize);
to->sb_logsunit = cpu_to_be32(from->sb_logsunit);
+
+ /*
+ * We need to ensure that bad_features2 always matches features2.
+ * Hence we enforce that here rather than having to remember to do it
+ * everywhere else that updates features2.
+ */
+ from->sb_bad_features2 = from->sb_features2;
to->sb_features2 = cpu_to_be32(from->sb_features2);
to->sb_bad_features2 = cpu_to_be32(from->sb_bad_features2);

diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 5ef9aa2..4fa80e6 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -640,25 +640,24 @@ xfs_mountfs(
xfs_sb_mount_common(mp, sbp);

/*
- * Check for a mismatched features2 values. Older kernels
- * read & wrote into the wrong sb offset for sb_features2
- * on some platforms due to xfs_sb_t not being 64bit size aligned
- * when sb_features2 was added, which made older superblock
- * reading/writing routines swap it as a 64-bit value.
+ * Check for a mismatched features2 values. Older kernels read & wrote
+ * into the wrong sb offset for sb_features2 on some platforms due to
+ * xfs_sb_t not being 64bit size aligned when sb_features2 was added,
+ * which made older superblock reading/writing routines swap it as a
+ * 64-bit value.
*
* For backwards compatibility, we make both slots equal.
*
- * If we detect a mismatched field, we OR the set bits into the
- * existing features2 field in case it has already been modified; we
- * don't want to lose any features. We then update the bad location
- * with the ORed value so that older kernels will see any features2
- * flags, and mark the two fields as needing updates once the
- * transaction subsystem is online.
+ * If we detect a mismatched field, we OR the set bits into the existing
+ * features2 field in case it has already been modified; we don't want
+ * to lose any features. We then update the bad location with the ORed
+ * value so that older kernels will see any features2 flags. The
+ * superblock writeback code ensures the new sb_features2 is copied to
+ * sb_bad_features2 before it is logged or written to disk.
*/
if (xfs_sb_has_mismatched_features2(sbp)) {
xfs_warn(mp, "correcting sb_features alignment problem");
sbp->sb_features2 |= sbp->sb_bad_features2;
- sbp->sb_bad_features2 = sbp->sb_features2;
mp->m_update_sb = true;

/*
--
2.0.0