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[PATCH] md: new sysfs interface for setting bits in the write-intent-bitmap

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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 <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Paul Clements 2006-10-03 01:15:49 -07:00 • committed by Linus Torvalds
commit 9b1d1dac18
4 changed files with 56 additions and 0 deletions
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9
Documentation/md.txt
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@ -410,6 +410,15 @@ also have
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