linux-kernel - Re: [PATCH v2 6/8] zram: change zcomp

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Date:	Thu, 27 Aug 2015 11:14:36 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Joonsoo Kim <js1304@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>,
	Nitin Gupta <ngupta@...are.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Stephan Mueller <smueller@...onox.de>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 6/8] zram: change zcomp_compress interface

On (08/20/15 15:35), Joonsoo Kim wrote:
> zram regards zstrm's buffer as compression destination buffer, but,
> it is not intuitive and there is no document about it. Providing
> destination buffer to zcomp_compress() directly seems more intuitive
> interface to me so this patch changes zcomp_compress interface.
> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> ---
>  drivers/block/zram/zcomp.c    | 5 ++---
>  drivers/block/zram/zcomp.h    | 2 +-
>  drivers/block/zram/zram_drv.c | 2 +-
>  3 files changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> index 965d1af..2ad504b 100644
> --- a/drivers/block/zram/zcomp.c
> +++ b/drivers/block/zram/zcomp.c
> @@ -307,10 +307,9 @@ void zcomp_strm_release(struct zcomp *comp, struct zcomp_strm *zstrm)
>  }
>  
>  int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
> -		const unsigned char *src, size_t *dst_len)
> +		const unsigned char *src, unsigned char *dst, size_t *dst_len)
>  {
> -	return comp->backend->compress(src, zstrm->buffer, dst_len,
> -			zstrm->private);
> +	return comp->backend->compress(src, dst, dst_len, zstrm->private);
>  }
>  
>  int zcomp_decompress(struct zcomp *comp, const unsigned char *src,
> diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
> index 46e2b9f..b2388e0 100644
> --- a/drivers/block/zram/zcomp.h
> +++ b/drivers/block/zram/zcomp.h
> @@ -60,7 +60,7 @@ struct zcomp_strm *zcomp_strm_find(struct zcomp *comp);
>  void zcomp_strm_release(struct zcomp *comp, struct zcomp_strm *zstrm);
>  
>  int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
> -		const unsigned char *src, size_t *dst_len);
> +		const unsigned char *src, unsigned char *dst, size_t *dst_len);
>  
>  int zcomp_decompress(struct zcomp *comp, const unsigned char *src,
>  		size_t src_len, unsigned char *dst);
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index b088ca9..4801e4d 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -701,7 +701,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>  		goto out;
>  	}
>  
> -	ret = zcomp_compress(zram->comp, zstrm, uncmem, &clen);
> +	ret = zcomp_compress(zram->comp, zstrm, uncmem, zstrm->buffer, &clen);

No, this change is unreasonable. zcomp might want to do with zstrm
anything it wants to, because zstrm belongs there. Besides, you change
zcomp_decompress() to require `struct zcomp_strm *zstrm', so let's
stick with this -- pass `struct zcomp_strm *zstrm' to both compress and
decompress functions. It's up to zcomp to ignore passed zstrm or do
something sane; not up to zram_drv.

	-ss
--
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