design: fix computation of buffer log item bitmap size
Wengang Wang was trying to work through a buffer log item by consulting
the ondisk format documentation, and was confused by the formula given
in section 14.3.14 regarding the size of blf_data_map, aka the dirty
bitmap for buffer log items. We noticed that the documentation doesn't
match what the kernel actually does, so let's fix this.
Reported-by: Wengang Wang <wen.gang.wang@oracle.com>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Chandan Babu R <chandan.babu@oracle.com>
diff --git a/design/XFS_Filesystem_Structure/journaling_log.asciidoc b/design/XFS_Filesystem_Structure/journaling_log.asciidoc
index 8421a53..ddcb87f 100644
--- a/design/XFS_Filesystem_Structure/journaling_log.asciidoc
+++ b/design/XFS_Filesystem_Structure/journaling_log.asciidoc
@@ -867,7 +867,7 @@
This variable-sized array acts as a dirty bitmap for the logged buffer. Each
1 bit represents a dirty region in the buffer, and each run of 1 bits
corresponds to a subsequent log item containing the new contents of the buffer
-area. Each bit represents +(blf_len * 512) / (blf_map_size * NBBY)+ bytes.
+area. Each bit represents +XFS_BLF_CHUNK+ (i.e. 128) bytes.
[[Buffer_Data_Log_Item]]
=== Buffer Data Log Item
