xfs: only CIL pushes require a start record

So move the one-off start record writing in xlog_write() out into
the static header that the CIL push builds to write into the log
initially. This simplifes the xlog_write() logic a lot.

pahole on x86-64 confirms that the xlog_cil_trans_hdr is correctly
32 bit aligned and packed for copying the log op and transaction
headers directly into the log as a single log region copy.

struct xlog_cil_trans_hdr {
        struct xlog_op_header      oph[2];               /*     0    24 */
        struct xfs_trans_header    thdr;                 /*    24    16 */
        struct xfs_log_iovec       lhdr[2];              /*    40    32 */

        /* size: 72, cachelines: 2, members: 3 */
        /* last cacheline: 8 bytes */
};

A wart is needed to handle the fact that length of the region the
opheader points to doesn't include the opheader length. hence if
we embed the opheader, we have to substract the opheader length from
the length written into the opheader by the generic copying code.
This will eventually go away when everything is converted to
embedded opheaders.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chandan Babu R <chandan.babu@oracle.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 45 insertions, 45 deletions

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 499e15b24215..f6fa5426278b 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -2221,9 +2221,9 @@ xlog_print_trans(
 }
 
 /*
- * Calculate the potential space needed by the log vector.  We may need a start
- * record, and each region gets its own struct xlog_op_header and may need to be
- * double word aligned.
+ * Calculate the potential space needed by the log vector. If this is a start
+ * transaction, the caller has already accounted for both opheaders in the start
+ * transaction, so we don't need to account for them here.
  */
 static int
 xlog_write_calc_vec_length(
@@ -2236,9 +2236,6 @@ xlog_write_calc_vec_length(
 	int			len = 0;
 	int			i;
 
-	if (optype & XLOG_START_TRANS)
-		headers++;
-
 	for (lv = log_vector; lv; lv = lv->lv_next) {
 		/* we don't write ordered log vectors */
 		if (lv->lv_buf_len == XFS_LOG_VEC_ORDERED)
@@ -2254,24 +2251,20 @@ xlog_write_calc_vec_length(
 		}
 	}
 
+	/* Don't account for regions with embedded ophdrs */
+	if (optype && headers > 0) {
+		if (optype & XLOG_START_TRANS) {
+			ASSERT(headers >= 2);
+			headers -= 2;
+		}
+	}
+
 	ticket->t_res_num_ophdrs += headers;
 	len += headers * sizeof(struct xlog_op_header);
 
 	return len;
 }
 
-static void
-xlog_write_start_rec(
-	struct xlog_op_header	*ophdr,
-	struct xlog_ticket	*ticket)
-{
-	ophdr->oh_tid	= cpu_to_be32(ticket->t_tid);
-	ophdr->oh_clientid = ticket->t_clientid;
-	ophdr->oh_len = 0;
-	ophdr->oh_flags = XLOG_START_TRANS;
-	ophdr->oh_res2 = 0;
-}
-
 static xlog_op_header_t *
 xlog_write_setup_ophdr(
 	struct xlog		*log,
@@ -2467,9 +2460,11 @@ xlog_write(
 	 * If this is a commit or unmount transaction, we don't need a start
 	 * record to be written.  We do, however, have to account for the
 	 * commit or unmount header that gets written. Hence we always have
-	 * to account for an extra xlog_op_header here.
+	 * to account for an extra xlog_op_header here for commit and unmount
+	 * records.
 	 */
-	ticket->t_curr_res -= sizeof(struct xlog_op_header);
+	if (optype & (XLOG_COMMIT_TRANS | XLOG_UNMOUNT_TRANS))
+		ticket->t_curr_res -= sizeof(struct xlog_op_header);
 	if (ticket->t_curr_res < 0) {
 		xfs_alert_tag(log->l_mp, XFS_PTAG_LOGRES,
 		     "ctx ticket reservation ran out. Need to up reservation");
@@ -2510,7 +2505,7 @@ xlog_write(
 			int			copy_len;
 			int			copy_off;
 			bool			ordered = false;
-			bool			wrote_start_rec = false;
+			bool			added_ophdr = false;
 
 			/* ordered log vectors have no regions to write */
 			if (lv->lv_buf_len == XFS_LOG_VEC_ORDERED) {
@@ -2524,25 +2519,24 @@ xlog_write(
 			ASSERT((unsigned long)ptr % sizeof(int32_t) == 0);
 
 			/*
-			 * Before we start formatting log vectors, we need to
-			 * write a start record. Only do this for the first
-			 * iclog we write to.
+			 * The XLOG_START_TRANS has embedded ophdrs for the
+			 * start record and transaction header. They will always
+			 * be the first two regions in the lv chain.
 			 */
 			if (optype & XLOG_START_TRANS) {
-				xlog_write_start_rec(ptr, ticket);
-				xlog_write_adv_cnt(&ptr, &len, &log_offset,
-						sizeof(struct xlog_op_header));
-				optype &= ~XLOG_START_TRANS;
-				wrote_start_rec = true;
-			}
-
-			ophdr = xlog_write_setup_ophdr(log, ptr, ticket, optype);
-			if (!ophdr)
-				return -EIO;
+				ophdr = reg->i_addr;
+				if (index)
+					optype &= ~XLOG_START_TRANS;
+			} else {
+				ophdr = xlog_write_setup_ophdr(log, ptr,
+							ticket, optype);
+				if (!ophdr)
+					return -EIO;
 
-			xlog_write_adv_cnt(&ptr, &len, &log_offset,
+				xlog_write_adv_cnt(&ptr, &len, &log_offset,
 					   sizeof(struct xlog_op_header));
-
+				added_ophdr = true;
+			}
 			len += xlog_write_setup_copy(ticket, ophdr,
 						     iclog->ic_size-log_offset,
 						     reg->i_len,
@@ -2551,13 +2545,22 @@ xlog_write(
 						     &partial_copy_len);
 			xlog_verify_dest_ptr(log, ptr);
 
+
+			/*
+			 * Wart: need to update length in embedded ophdr not
+			 * to include it's own length.
+			 */
+			if (!added_ophdr) {
+				ophdr->oh_len = cpu_to_be32(copy_len -
+						sizeof(struct xlog_op_header));
+			}
 			/*
 			 * Copy region.
 			 *
-			 * Unmount records just log an opheader, so can have
-			 * empty payloads with no data region to copy. Hence we
-			 * only copy the payload if the vector says it has data
-			 * to copy.
+			 * Commit and unmount records just log an opheader, so
+			 * we can have empty payloads with no data region to
+			 * copy.  Hence we only copy the payload if the vector
+			 * says it has data to copy.
 			 */
 			ASSERT(copy_len >= 0);
 			if (copy_len > 0) {
@@ -2565,12 +2568,9 @@ xlog_write(
 				xlog_write_adv_cnt(&ptr, &len, &log_offset,
 						   copy_len);
 			}
-			copy_len += sizeof(struct xlog_op_header);
-			record_cnt++;
-			if (wrote_start_rec) {
+			if (added_ophdr)
 				copy_len += sizeof(struct xlog_op_header);
-				record_cnt++;
-			}
+			record_cnt++;
 			data_cnt += contwr ? copy_len : 0;
 
 			error = xlog_write_copy_finish(log, iclog, optype,