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Old 05-12-2010, 04:58 AM
Mikulas Patocka
 
Default fix hard-coded disk header chunk size for persistent snapshot

On Wed, 12 May 2010, Alasdair G Kergon wrote:

> On Wed, May 12, 2010 at 10:29:22AM +0900, Tomohiro Kusumi wrote:
> > This patch fixes hard-coded value for the size of a chunk that includes
> > disk header for persistent snapshot. It should be changed to existing
> > macro NUM_SNAPSHOT_HDR_CHUNKS instead of using hard-coded value 1.
>
> Any more places too? (E.g. persistent_commit_merge)
>
> Alasdair

I think the expression in persistent_commit_merge should be changed to:
ps->next_free = area_location(ps, ps->current_area) +
ps->current_committed + 1;

It is numerically the same, but will avoid trouble if
NUM_SNAPSHOT_HDR_CHUNKS is increased.

Mikulas

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Old 05-12-2010, 05:57 AM
Tomohiro Kusumi
 
Default fix hard-coded disk header chunk size for persistent snapshot

(2010/05/12 13:58), Mikulas Patocka wrote:



On Wed, 12 May 2010, Alasdair G Kergon wrote:


On Wed, May 12, 2010 at 10:29:22AM +0900, Tomohiro Kusumi wrote:

This patch fixes hard-coded value for the size of a chunk that includes
disk header for persistent snapshot. It should be changed to existing
macro NUM_SNAPSHOT_HDR_CHUNKS instead of using hard-coded value 1.


Any more places too? (E.g. persistent_commit_merge)

Alasdair


I think the expression in persistent_commit_merge should be changed to:
ps->next_free = area_location(ps, ps->current_area) +
ps->current_committed + 1;

It is numerically the same, but will avoid trouble if
NUM_SNAPSHOT_HDR_CHUNKS is increased.

Mikulas




agree,

a single chunk is large enough to contain 16byte disk header
which does not seem necessary to increase NUM_SNAPSHOT_HDR_CHUNKS in the future
(unless whole structure get totally changed),
but it should also get fixed to avoid trouble.

I merged it to the patch with your names signed off.

Thanks,
Tomohiro Kusumi


Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@jp.fujitsu.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
---

diff -aNur linux-2.6.34-rc7.org/drivers/md/dm-snap-persistent.c linux-2.6.34-rc7/drivers/md/dm-snap-persistent.c
--- linux-2.6.34-rc7.org/drivers/md/dm-snap-persistent.c 2010-05-10 10:36:28.000000000 +0900
+++ linux-2.6.34-rc7/drivers/md/dm-snap-persistent.c 2010-05-12 14:49:13.000000000 +0900
@@ -266,7 +266,7 @@
*/
static chunk_t area_location(struct pstore *ps, chunk_t area)
{
- return 1 + ((ps->exceptions_per_area + 1) * area);
+ return NUM_SNAPSHOT_HDR_CHUNKS + ((ps->exceptions_per_area + 1) * area);
}

/*

@@ -780,8 +780,8 @@
* ps->current_area does not get reduced by prepare_merge() until
* after commit_merge() has removed the nr_merged previous exceptions.
*/
- ps->next_free = (area_location(ps, ps->current_area) - 1) +
- (ps->current_committed + 1) + NUM_SNAPSHOT_HDR_CHUNKS;
+ ps->next_free = area_location(ps, ps->current_area) +
+ ps->current_committed + 1;

return 0;

}

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