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Date: Fri, 7 Mar 2014 12:20:45 +0300
From: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To: Minchan Kim <minchan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, Nitin Gupta <ngupta@...are.org>,
Jerome Marchand <jmarchan@...hat.com>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH] zram: propagate error to user
On (03/07/14 10:56), Minchan Kim wrote:
> When we initialized zcomp with single, we couldn't change
> max_comp_streams without zram reset but current interface doesn't
> show any error to user and even it changes max_comp_streams's value
> without any effect so it would make user very confusing.
>
> This patch prevents max_comp_streams's change when zcomp was
> initialized as single zcomp and emit the error to user(ex, echo).
>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
> Documentation/blockdev/zram.txt | 9 +++++----
> drivers/block/zram/zcomp.c | 10 +++++-----
> drivers/block/zram/zcomp.h | 4 ++--
> drivers/block/zram/zram_drv.c | 15 +++++++++++----
> 4 files changed, 23 insertions(+), 15 deletions(-)
>
> diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
> index 2604ffed51db..0595c3f56ccf 100644
> --- a/Documentation/blockdev/zram.txt
> +++ b/Documentation/blockdev/zram.txt
> @@ -37,10 +37,11 @@ Note:
> In order to enable compression backend's multi stream support max_comp_streams
> must be initially set to desired concurrency level before ZRAM device
> initialisation. Once the device initialised as a single stream compression
> -backend (max_comp_streams equals to 0) changing the value of max_comp_streams
> -will not take any effect, because single stream compression backend implemented
> -as a special case and does not support dynamic max_comp_streams. Only multi
> -stream backend supports dynamic max_comp_streams adjustment.
> +backend (max_comp_streams equals to 1), you will see error if you try to change
> +the value of max_comp_streams because single stream compression backend
> +implemented as a special case by lock overhead issue and does not support
> +dynamic max_comp_streams. Only multi stream backend supports dynamic
> +max_comp_streams adjustment.
>
> 3) Select compression algorithm
> Using comp_algorithm device attribute one can see available and
> diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> index 92a83df40a27..15fe6a27781b 100644
> --- a/drivers/block/zram/zcomp.c
> +++ b/drivers/block/zram/zcomp.c
> @@ -152,7 +152,7 @@ static void zcomp_strm_multi_release(struct zcomp *comp, struct zcomp_strm *zstr
> }
>
> /* change max_strm limit */
> -static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
> +static bool zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
> {
> struct zcomp_strm_multi *zs = comp->stream;
> struct zcomp_strm *zstrm;
> @@ -171,7 +171,7 @@ static int zcomp_strm_multi_set_max_streams(struct zcomp *comp, int num_strm)
> zs->avail_strm--;
> }
> spin_unlock(&zs->strm_lock);
> - return 0;
> + return true;
> }
>
> static void zcomp_strm_multi_destroy(struct zcomp *comp)
> @@ -231,10 +231,10 @@ static void zcomp_strm_single_release(struct zcomp *comp,
> mutex_unlock(&zs->strm_lock);
> }
>
> -static int zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
> +static bool zcomp_strm_single_set_max_streams(struct zcomp *comp, int num_strm)
> {
> /* zcomp_strm_single support only max_comp_streams == 1 */
> - return -ENOTSUPP;
> + return 0;
> }
IMHO, -ENOTSUPP for unsupported operation fits better than `false'.
yes, currently there are only two possible returns:
0 -- success
-ENOTSUPP - not supported operation
though, we can extend functions later and return additional codes, other
than `false' and `true'.
for example, -E2BIG if user requested extremly large number of streams,
like 5000 streams.
>
> static void zcomp_strm_single_destroy(struct zcomp *comp)
> @@ -283,7 +283,7 @@ ssize_t zcomp_available_show(const char *comp, char *buf)
> return sz;
> }
>
> -int zcomp_set_max_streams(struct zcomp *comp, int num_strm)
> +bool zcomp_set_max_streams(struct zcomp *comp, int num_strm)
> {
> return comp->set_max_streams(comp, num_strm);
> }
> diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
> index 8b8997f8613b..c59d1fca72c0 100644
> --- a/drivers/block/zram/zcomp.h
> +++ b/drivers/block/zram/zcomp.h
> @@ -46,7 +46,7 @@ struct zcomp {
>
> struct zcomp_strm *(*strm_find)(struct zcomp *comp);
> void (*strm_release)(struct zcomp *comp, struct zcomp_strm *zstrm);
> - int (*set_max_streams)(struct zcomp *comp, int num_strm);
> + bool (*set_max_streams)(struct zcomp *comp, int num_strm);
> void (*destroy)(struct zcomp *comp);
> };
>
> @@ -64,5 +64,5 @@ int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
> int zcomp_decompress(struct zcomp *comp, const unsigned char *src,
> size_t src_len, unsigned char *dst);
>
> -int zcomp_set_max_streams(struct zcomp *comp, int num_strm);
> +bool zcomp_set_max_streams(struct zcomp *comp, int num_strm);
> #endif /* _ZCOMP_H_ */
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 7631ef0cbc41..eead9db9b100 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -128,17 +128,24 @@ static ssize_t max_comp_streams_store(struct device *dev,
> struct zram *zram = dev_to_zram(dev);
>
> if (kstrtoint(buf, 0, &num))
> - return -EINVAL;
> + goto out;
> if (num < 1)
> - return -EINVAL;
> + goto out;
> +
> down_write(&zram->init_lock);
> if (init_done(zram)) {
> - if (zcomp_set_max_streams(zram->comp, num))
> + if (!zcomp_set_max_streams(zram->comp, num)) {
> pr_info("Cannot change max compression streams\n");
> + goto out_unlock;
> + }
> }
> +
> zram->max_comp_streams = num;
agree, better to avoid this for a single stream.
> - up_write(&zram->init_lock);
> return len;
> +out_unlock:
> + up_write(&zram->init_lock);
> +out:
> + return -EINVAL;
> }
>
> static ssize_t comp_algorithm_show(struct device *dev,
> --
> 1.9.0
>
--
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