xfs: support a crc verification only log record pass

Log recovery torn write detection uses CRC verification over a range of
the active log to identify torn writes. Since the generic log recovery
pass code implements a superset of the functionality required for CRC
verification, it can be easily modified to support a CRC verification
only pass.

Create a new CRC pass type and update the log record processing helper
to skip everything beyond CRC verification when in this mode. This pass
will be invoked in subsequent patches to implement torn write detection.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

2 files changed, 20 insertions, 5 deletions

diff --git a/fs/xfs/libxfs/xfs_log_recover.h b/fs/xfs/libxfs/xfs_log_recover.h
index 1c55ccbb379d..8e385f91d660 100644
--- a/fs/xfs/libxfs/xfs_log_recover.h
+++ b/fs/xfs/libxfs/xfs_log_recover.h
@@ -60,6 +60,7 @@ typedef struct xlog_recover {
  */
 #define XLOG_BC_TABLE_SIZE      64
 
+#define XLOG_RECOVER_CRCPASS    0
 #define XLOG_RECOVER_PASS1      1
 #define XLOG_RECOVER_PASS2      2
 
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index e0318e8a0771..1be259044096 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -4159,13 +4159,27 @@ xlog_recover_process(
         int                     error;
         __le32                  crc;
 
+        crc = xlog_cksum(log, rhead, dp, be32_to_cpu(rhead->h_len));
+
         /*
-         * Check the CRC and issue a warning if and only if the CRC in the
-         * header is non-zero. This is an advisory warning and the zero CRC
-         * check prevents warnings from being emitted when upgrading the kernel
-         * from one that does not add CRCs by default.
+         * Nothing else to do if this is a CRC verification pass. Just return
+         * if this a record with a non-zero crc. Unfortunately, mkfs always
+         * sets h_crc to 0 so we must consider this valid even on v5 supers.
+         * Otherwise, return EFSBADCRC on failure so the callers up the stack
+         * know precisely what failed.
+         */
+        if (pass == XLOG_RECOVER_CRCPASS) {
+                if (rhead->h_crc && crc != le32_to_cpu(rhead->h_crc))
+                        return -EFSBADCRC;
+                return 0;
+        }
+
+        /*
+         * We're in the normal recovery path. Issue a warning if and only if the
+         * CRC in the header is non-zero. This is an advisory warning and the
+         * zero CRC check prevents warnings from being emitted when upgrading
+         * the kernel from one that does not add CRCs by default.
          */
-        crc = xlog_cksum(log, rhead, dp, be32_to_cpu(rhead->h_len));
         if (crc != le32_to_cpu(rhead->h_crc)) {
                 if (rhead->h_crc || xfs_sb_version_hascrc(&log->l_mp->m_sb)) {
                         xfs_alert(log->l_mp,