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[PATCH] dm snapshot: tidy snapshot_map

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This patch rearranges the snapshot_map code so that the functional changes in
subsequent patches are clearer.

The only functional change is to replace the existing read lock with a write
lock which the next patch needs.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Alasdair G Kergon 2006-10-03 01:15:28 -07:00 committed by Linus Torvalds
parent 927ffe7c9a
commit ba40a2aa6e
1 changed files with 26 additions and 46 deletions
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72
drivers/md/dm-snap.c
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@ -851,7 +851,6 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
{
struct exception *e;
struct dm_snapshot *s = (struct dm_snapshot *) ti->private;
int copy_needed = 0;
int r = 1;
chunk_t chunk;
struct pending_exception *pe = NULL;
@ -866,29 +865,28 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
if (unlikely(bio_barrier(bio)))
return -EOPNOTSUPP;
/* FIXME: should only take write lock if we need
* to copy an exception */
down_write(&s->lock);
if (!s->valid) {
r = -EIO;
goto out_unlock;
}
/* If the block is already remapped - use that, else remap it */
e = lookup_exception(&s->complete, chunk);
if (e) {
remap_exception(s, e, bio);
goto out_unlock;
}
/*
* Write to snapshot - higher level takes care of RW/RO
* flags so we should only get this if we are
* writeable.
*/
if (bio_rw(bio) == WRITE) {
/* FIXME: should only take write lock if we need
* to copy an exception */
down_write(&s->lock);
if (!s->valid) {
r = -EIO;
goto out_unlock;
}
/* If the block is already remapped - use that, else remap it */
e = lookup_exception(&s->complete, chunk);
if (e) {
remap_exception(s, e, bio);
goto out_unlock;
}
pe = __find_pending_exception(s, bio);
if (!pe) {
__invalidate_snapshot(s, pe, -ENOMEM);
@ -899,45 +897,27 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
remap_exception(s, &pe->e, bio);
bio_list_add(&pe->snapshot_bios, bio);
r = 0;
if (!pe->started) {
/* this is protected by snap->lock */
pe->started = 1;
copy_needed = 1;
}
r = 0;
out_unlock:
up_write(&s->lock);
if (copy_needed)
up_write(&s->lock);
start_copy(pe);
} else {
goto out;
}
} else
/*
* FIXME: this read path scares me because we
* always use the origin when we have a pending
* exception. However I can't think of a
* situation where this is wrong - ejt.
*/
bio->bi_bdev = s->origin->bdev;
/* Do reads */
down_read(&s->lock);
if (!s->valid) {
up_read(&s->lock);
return -EIO;
}
/* See if it it has been remapped */
e = lookup_exception(&s->complete, chunk);
if (e)
remap_exception(s, e, bio);
else
bio->bi_bdev = s->origin->bdev;
up_read(&s->lock);
}
out_unlock:
up_write(&s->lock);
out:
return r;
}