xfsdocs: clarify log item header structure

Commit Message

Darrick J. Wong Nov. 29, 2017, 1:48 a.m. UTC

From: Darrick J. Wong <[e-mail]>

Make it more explicit that each log item has to start with a type code
and size, except for transaction headers.

Signed-off-by: Darrick J. Wong <[e-mail]>
---
 .../journaling_log.asciidoc                        |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--
To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
the body of a message to [e-mail]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Patch

diff --git a/design/XFS_Filesystem_Structure/journaling_log.asciidoc b/design/XFS_Filesystem_Structure/journaling_log.asciidoc
index 0aec036..6109458 100644
--- a/design/XFS_Filesystem_Structure/journaling_log.asciidoc
+++ b/design/XFS_Filesystem_Structure/journaling_log.asciidoc
@@ -217,6 +217,18 @@  magic number to distinguish themselves.  Buffer data items only appear after
 | +XFS_LI_BUD+			| 0x1245        | xref:BUD_Log_Item[File Block Mapping Update Done]
 |=====
 
+Note that all log items (except for transaction headers) MUST start with
+the following header structure.  The type and size fields are baked into
+each log item header, but there is not a separately defined header.
+
+[source, c]
+----
+struct xfs_log_item {
+     __uint16_t                magic;
+     __uint16_t                size;
+};
+----
+
 [[Log_Transaction_Headers]]
 === Transaction Headers