[PATCH] xfsdocs: fix extent record format image

["Darrick J. Wong" <djwong@kernel.org>]

From: Xiaole He <hexiaole@kylinos.cn>

The image of 'design/XFS_Filesystem_Structure/images/31.png' depicts
extent record format as below:

+----+-------------------------+---------------------+------------+
|flag|bits 72 to 126(54)       |bits 21 to 72(52)    |bit 0-20(21)|
|    |logical file block offset|absolute block number|# blocks    |
+----+-------------------------+---------------------+------------+

There has a typo for 'logical file block offset' part, it writes 'bits
72 to 126', but it should be 'bits 73 to 126' because the 72st bit is
consumed by 'absolute block number' part, this patch fix this problem
and redrawing the image as below:

+---------+-------------------------+---------------------+----------+
|bits[127]|bits[73-126]             |bits[21-72]          |bits[0-20]|
+---------+-------------------------+---------------------+----------+
|flag     |logical file block offset|absolute block number|# blocks  |
+---------+-------------------------+---------------------+----------+

Signed-off-by: Xiaole He <hexiaole@kylinos.cn>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
[djwong: convert the raw table above into asciidoc and remove the png]
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
Originally this patch was against 31.png itself, but apparently vger has
been eating the entire thread because spam.  It's very annoying that
vger still lets through plenty of spam and phishing attempts while
blocking legitimate patch submissions.

Since there's nothing I can do about our crap infrastructure, I've taken
the original patch submitter's table from the commit description and
converted that directly into an asciidoc table format.  I'll remove the
PNG when I commit this patch, but I'm not including it here because you
can't spell terrible without IT.

--D
---
 .../XFS_Filesystem_Structure/data_extents.asciidoc |   14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/design/XFS_Filesystem_Structure/data_extents.asciidoc b/design/XFS_Filesystem_Structure/data_extents.asciidoc
index 4f1109b..29c78fe 100644
--- a/design/XFS_Filesystem_Structure/data_extents.asciidoc
+++ b/design/XFS_Filesystem_Structure/data_extents.asciidoc
@@ -17,7 +17,19 @@ vary depending on the extent allocator used in the XFS driver.
 An extent is 128 bits in size and uses the following packed layout:
 
 .Extent record format
-image::images/31.png[]
+
+[cols="1,1,1,1"]
+|===
+|bit[127]
+|bits[73-126]
+|bits[21-72]
+|bits[0-20]
+
+|flag
+|logical file block offset
+|absolute block number
+|# of blocks
+|===
 
 The extent is represented by the +xfs_bmbt_rec+ structure which uses a big
 endian format on-disk. In-core management of extents use the +xfs_bmbt_irec+