[PATCH 24/45] xfs: move log iovec alignment to preparation function

[Dave Chinner <david@fromorbit.com>]

From: Dave Chinner <dchinner@redhat.com>

To include log op headers directly into the log iovec regions that
the ophdrs wrap, we need to move the buffer alignment code from
xlog_finish_iovec() to xlog_prepare_iovec(). This is because the
xlog_op_header is only 12 bytes long, and we need the buffer that
the caller formats their data into to be 8 byte aligned.

Hence once we start prepending the ophdr in xlog_prepare_iovec(), we
are going to need to manage the padding directly to ensure that the
buffer pointer returned is correctly aligned.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/xfs_log.h | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/fs/xfs/xfs_log.h b/fs/xfs/xfs_log.h
index c0c3141944ea..1ca4f2edbdaf 100644
--- a/fs/xfs/xfs_log.h
+++ b/fs/xfs/xfs_log.h
@@ -21,6 +21,16 @@ struct xfs_log_vec {
 
 #define XFS_LOG_VEC_ORDERED	(-1)
 
+/*
+ * We need to make sure the buffer pointer returned is naturally aligned for the
+ * biggest basic data type we put into it. We have already accounted for this
+ * padding when sizing the buffer.
+ *
+ * However, this padding does not get written into the log, and hence we have to
+ * track the space used by the log vectors separately to prevent log space hangs
+ * due to inaccurate accounting (i.e. a leak) of the used log space through the
+ * CIL context ticket.
+ */
 static inline void *
 xlog_prepare_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec **vecp,
 		uint type)
@@ -34,6 +44,9 @@ xlog_prepare_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec **vecp,
 		vec = &lv->lv_iovecp[0];
 	}
 
+	if (!IS_ALIGNED(lv->lv_buf_len, sizeof(uint64_t)))
+		lv->lv_buf_len = round_up(lv->lv_buf_len, sizeof(uint64_t));
+
 	vec->i_type = type;
 	vec->i_addr = lv->lv_buf + lv->lv_buf_len;
 
@@ -43,20 +56,10 @@ xlog_prepare_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec **vecp,
 	return vec->i_addr;
 }
 
-/*
- * We need to make sure the next buffer is naturally aligned for the biggest
- * basic data type we put into it.  We already accounted for this padding when
- * sizing the buffer.
- *
- * However, this padding does not get written into the log, and hence we have to
- * track the space used by the log vectors separately to prevent log space hangs
- * due to inaccurate accounting (i.e. a leak) of the used log space through the
- * CIL context ticket.
- */
 static inline void
 xlog_finish_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec *vec, int len)
 {
-	lv->lv_buf_len += round_up(len, sizeof(uint64_t));
+	lv->lv_buf_len += len;
 	lv->lv_bytes += len;
 	vec->i_len = len;
 }
-- 
2.28.0