[PATCH] md: new sysfs interface for setting bits in the write-intent-bitmap
Add a new sysfs interface that allows the bitmap of an array to be dirtied.
The interface is write-only, and is used as follows:
echo "1000" > /sys/block/md2/md/bitmap
(dirty the bit for chunk 1000 [offset 0] in the in-memory and on-disk
bitmaps of array md2)
echo "1000-2000" > /sys/block/md1/md/bitmap
(dirty the bits for chunks 1000-2000 in md1's bitmap)
This is useful, for example, in cluster environments where you may need to
combine two disjoint bitmaps into one (following a server failure, after a
secondary server has taken over the array). By combining the bitmaps on
the two servers, a full resync can be avoided (This was discussed on the
list back on March 18, 2005, "[PATCH 1/2] md bitmap bug fixes" thread).
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/Documentation/md.txt b/Documentation/md.txt
index 0668f9d..084ecf4e 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -410,6 +410,15 @@
than sectors, this my be larger than the number of actual errors
by a factor of the number of sectors in a page.
+ bitmap_set_bits
+ If the array has a write-intent bitmap, then writing to this
+ attribute can set bits in the bitmap, indicating that a resync
+ would need to check the corresponding blocks. Either individual
+ numbers or start-end pairs can be written. Multiple numbers
+ can be separated by a space.
+ Note that the numbers are 'bit' numbers, not 'block' numbers.
+ They should be scaled by the bitmap_chunksize.
+
Each active md device may also have attributes specific to the
personality module that manages it.
These are specific to the implementation of the module and could