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[PATCH v3 3/5] xfs: fix segment in xfs_buf_item_format_segment

To: xfs@xxxxxxxxxxx
Subject: [PATCH v3 3/5] xfs: fix segment in xfs_buf_item_format_segment
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Tue, 04 Dec 2012 17:18:04 -0600
References: <20121204231801.982422341@xxxxxxx>
User-agent: quilt/0.51-1
Not every segment in a multi-segment buffer is dirty in a
transaction and they will not be outputted. The assert in
xfs_buf_item_format_segment() that checks for the at least
one chunk of data in the segment to be used is not necessary
true for multi-segmented buffers.

Signed-off-by: Mark Tinguely <tinguely@xxxxxxx>
---
 fs/xfs/xfs_buf_item.c |   20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

Index: b/fs/xfs/xfs_buf_item.c
===================================================================
--- a/fs/xfs/xfs_buf_item.c
+++ b/fs/xfs/xfs_buf_item.c
@@ -287,6 +287,17 @@ xfs_buf_item_format_segment(
         */
        base_size = offsetof(struct xfs_buf_log_format, blf_data_map) +
                        (blfp->blf_map_size * sizeof(blfp->blf_data_map[0]));
+
+       nvecs = 0;
+       first_bit = xfs_next_bit(blfp->blf_data_map, blfp->blf_map_size, 0);
+       if (!(bip->bli_flags & XFS_BLI_STALE) && first_bit == -1) {
+               /*
+                * If the map is not be dirty in the transaction, mark
+                * the size as zero and do not advance the vector pointer.
+                */
+               goto out;
+       }
+
        vecp->i_addr = blfp;
        vecp->i_len = base_size;
        vecp->i_type = XLOG_REG_TYPE_BFORMAT;
@@ -301,15 +312,13 @@ xfs_buf_item_format_segment(
                 */
                trace_xfs_buf_item_format_stale(bip);
                ASSERT(blfp->blf_flags & XFS_BLF_CANCEL);
-               blfp->blf_size = nvecs;
-               return vecp;
+               goto out;
        }
 
        /*
         * Fill in an iovec for each set of contiguous chunks.
         */
-       first_bit = xfs_next_bit(blfp->blf_data_map, blfp->blf_map_size, 0);
-       ASSERT(first_bit != -1);
+
        last_bit = first_bit;
        nbits = 1;
        for (;;) {
@@ -371,7 +380,8 @@ xfs_buf_item_format_segment(
                        nbits++;
                }
        }
-       bip->__bli_format.blf_size = nvecs;
+out:
+       blfp->blf_size = nvecs;
        return vecp;
 }
 


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