Re: [PATCH] fix hard-coded disk header chunk size for persistentsnapshot

[Tomohiro Kusumi]

(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@xxxxxxxxxxxxxx>
Signed-off-by: Alasdair G Kergon <agk@xxxxxxxxxx>
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
---

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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