xfs: return start block of first bad log record during recovery

Each log recovery pass walks from the tail block to the head block and
processes records appropriately based on the associated log pass type.
There are various failure conditions that can occur through this
sequence, such as I/O errors, CRC errors, etc. Log torn write detection
will perform CRC verification near the head of the log to detect torn
writes and trim torn records from the log appropriately.

As it is, xlog_do_recovery_pass() only returns an error code in the
event of CRC failure, which isn't enough information to trim the head of
the log. Update xlog_do_recovery_pass() to optionally return the start
block of the associated record when an error occurs. This patch contains
no functional changes.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_log_recover.c

@@ -4239,10 +4239,12 @@ xlog_do_recovery_pass(
 	struct xlog		*log,
 	xfs_daddr_t		head_blk,
 	xfs_daddr_t		tail_blk,
-	int			pass)
+	int			pass,
+	xfs_daddr_t		*first_bad)	/* out: first bad log rec */
 {
 	xlog_rec_header_t	*rhead;
 	xfs_daddr_t		blk_no;
+	xfs_daddr_t		rhead_blk;
 	char			*offset;
 	xfs_buf_t		*hbp, *dbp;
 	int			error = 0, h_size, h_len;
@@ -4251,6 +4253,7 @@ xlog_do_recovery_pass(
 	struct hlist_head	rhash[XLOG_RHASH_SIZE];
 
 	ASSERT(head_blk != tail_blk);
+	rhead_blk = 0;
 
 	/*
 	 * Read the header of the tail block and get the iclog buffer size from
@@ -4325,7 +4328,7 @@ xlog_do_recovery_pass(
 	}
 
 	memset(rhash, 0, sizeof(rhash));
-	blk_no = tail_blk;
+	blk_no = rhead_blk = tail_blk;
 	if (tail_blk > head_blk) {
 		/*
 		 * Perform recovery around the end of the physical log.
@@ -4436,11 +4439,14 @@ xlog_do_recovery_pass(
 						     pass);
 			if (error)
 				goto bread_err2;
+
 			blk_no += bblks;
+			rhead_blk = blk_no;
 		}
 
 		ASSERT(blk_no >= log->l_logBBsize);
 		blk_no -= log->l_logBBsize;
+		rhead_blk = blk_no;
 	}
 
 	/* read first part of physical log */
@@ -4464,13 +4470,19 @@ xlog_do_recovery_pass(
 		error = xlog_recover_process(log, rhash, rhead, offset, pass);
 		if (error)
 			goto bread_err2;
+
 		blk_no += bblks + hblks;
+		rhead_blk = blk_no;
 	}
 
  bread_err2:
 	xlog_put_bp(dbp);
  bread_err1:
 	xlog_put_bp(hbp);
+
+	if (error && first_bad)
+		*first_bad = rhead_blk;
+
 	return error;
 }
 
@@ -4508,7 +4520,7 @@ xlog_do_log_recovery(
 		INIT_LIST_HEAD(&log->l_buf_cancel_table[i]);
 
 	error = xlog_do_recovery_pass(log, head_blk, tail_blk,
-				      XLOG_RECOVER_PASS1);
+				      XLOG_RECOVER_PASS1, NULL);
 	if (error != 0) {
 		kmem_free(log->l_buf_cancel_table);
 		log->l_buf_cancel_table = NULL;
@@ -4519,7 +4531,7 @@ xlog_do_log_recovery(
 	 * When it is complete free the table of buf cancel items.
 	 */
 	error = xlog_do_recovery_pass(log, head_blk, tail_blk,
-				      XLOG_RECOVER_PASS2);
+				      XLOG_RECOVER_PASS2, NULL);
 #ifdef DEBUG
 	if (!error) {
 		int	i;