linux-kernel - Re: [PATCH v4 06/13] dm snapshot: merge target should not allocate new exceptions

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Date:	Fri, 20 Nov 2009 15:54:16 -0500
From:	Mike Snitzer <snitzer@...hat.com>
To:	dm-devel@...hat.com
Cc:	Mikulas Patocka <mpatocka@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 06/13] dm snapshot: merge target should not allocate
 new exceptions

On Fri, Nov 20 2009 at  3:27pm -0500,
Mike Snitzer <snitzer@...hat.com> wrote:

> If a write request to a merging snapshot device is to be dispatched
> directly to the origin (because the chunk is not remapped or was already
> merged), snapshot_merge_map() must make exceptions in other snapshots.
...
> +static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
> +			      union map_info *map_context)
> +{
> +	struct dm_exception *e;
> +	struct dm_snapshot *s = ti->private;
> +	int r = DM_MAPIO_REMAPPED;
> +	chunk_t chunk;
> +
> +	chunk = sector_to_chunk(s->store, bio->bi_sector);
> +
> +	down_read(&s->lock);
> +
> +	/* Full snapshots are not usable */
> +	if (!s->valid) {
> +		r = -EIO;
> +		goto out_unlock;
> +	}
> +
> +	/* If the block is already remapped - use that */
> +	e = dm_lookup_exception(&s->complete, chunk);
> +	if (e) {
> +		remap_exception(s, e, bio, chunk);
> +		goto out_unlock;
> +	}
> +
> +	bio->bi_bdev = s->origin->bdev;
> +
> +	if (bio_rw(bio) == WRITE) {
> +		up_write(&s->lock);
> +		return do_origin(s->origin, bio);
> +	}

OK, I caught this in review but clearly didn't refresh the patch; the
above up_write() should be up_read().

Mike
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