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Subject: Re: [PATCH v3 4/4] scatterlist: add sgl_memset()
To:     Douglas Gilbert <dgilbert@interlog.com>,
        linux-scsi@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     martin.petersen@oracle.com, axboe@kernel.dk, bvanassche@acm.org
References: <20201019191928.77845-1-dgilbert@interlog.com>
 <20201019191928.77845-5-dgilbert@interlog.com>
From:   Bodo Stroesser <bostroesser@gmail.com>
Message-ID: <9a8ab6d9-72cf-1dd2-a9e8-114e7f9f198c@gmail.com>
Date:   Tue, 3 Nov 2020 14:28:48 +0100
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Am 19.10.20 um 21:19 schrieb Douglas Gilbert:
> The existing sg_zero_buffer() function is a bit restrictive.
> For example protection information (PI) blocks are usually
> initialized to 0xff bytes. As its name suggests sgl_memset()
> is modelled on memset(). One difference is the type of the
> val argument which is u8 rather than int. Plus it returns
> the number of bytes (over)written.
> 
> Change implementation of sg_zero_buffer() to call this new
> function.
> 
> Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
> ---
>   include/linux/scatterlist.h |  3 ++
>   lib/scatterlist.c           | 65 +++++++++++++++++++++++++------------
>   2 files changed, 48 insertions(+), 20 deletions(-)
> 
> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
> index ae260dc5fedb..a40012c8a4e6 100644
> --- a/include/linux/scatterlist.h
> +++ b/include/linux/scatterlist.h
> @@ -329,6 +329,9 @@ bool sgl_compare_sgl(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_sk
>   		     struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip,
>   		     size_t n_bytes);
>   
> +size_t sgl_memset(struct scatterlist *sgl, unsigned int nents, off_t skip,
> +		  u8 val, size_t n_bytes);
> +
>   /*
>    * Maximum number of entries that will be allocated in one piece, if
>    * a list larger than this is required then chaining will be utilized.
> diff --git a/lib/scatterlist.c b/lib/scatterlist.c
> index 49185536acba..6b430f7293e0 100644
> --- a/lib/scatterlist.c
> +++ b/lib/scatterlist.c
> @@ -952,26 +952,7 @@ EXPORT_SYMBOL(sg_pcopy_to_buffer);
>   size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents,
>   		       size_t buflen, off_t skip)
>   {
> -	unsigned int offset = 0;
> -	struct sg_mapping_iter miter;
> -	unsigned int sg_flags = SG_MITER_ATOMIC | SG_MITER_TO_SG;
> -
> -	sg_miter_start(&miter, sgl, nents, sg_flags);
> -
> -	if (!sg_miter_skip(&miter, skip))
> -		return false;
> -
> -	while (offset < buflen && sg_miter_next(&miter)) {
> -		unsigned int len;
> -
> -		len = min(miter.length, buflen - offset);
> -		memset(miter.addr, 0, len);
> -
> -		offset += len;
> -	}
> -
> -	sg_miter_stop(&miter);
> -	return offset;
> +	return sgl_memset(sgl, nents, skip, 0, buflen);
>   }
>   EXPORT_SYMBOL(sg_zero_buffer);
>   
> @@ -1110,3 +1091,47 @@ bool sgl_compare_sgl(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_sk
>   	return equ;
>   }
>   EXPORT_SYMBOL(sgl_compare_sgl);
> +
> +/**
> + * sgl_memset - set byte 'val' up to n_bytes times on SG list
> + * @sgl:		 The SG list
> + * @nents:		 Number of SG entries in sgl
> + * @skip:		 Number of bytes to skip before starting
> + * @val:		 byte value to write to sgl
> + * @n_bytes:		 The (maximum) number of bytes to modify
> + *
> + * Returns:
> + *   The number of bytes written.
> + *
> + * Notes:
> + *   Stops writing if either sgl or n_bytes is exhausted. If n_bytes is
> + *   set SIZE_MAX then val will be written to each byte until the end
> + *   of sgl.
> + *
> + *   The notes in sgl_copy_sgl() about large sgl_s _applies here as well.
> + *
> + **/
> +size_t sgl_memset(struct scatterlist *sgl, unsigned int nents, off_t skip,
> +		  u8 val, size_t n_bytes)
> +{
> +	size_t offset = 0;
> +	size_t len;
> +	struct sg_mapping_iter miter;
> +
> +	if (n_bytes == 0)
> +		return 0;
> +	sg_miter_start(&miter, sgl, nents, SG_MITER_ATOMIC | SG_MITER_TO_SG);
> +	if (!sg_miter_skip(&miter, skip))
> +		goto fini;
> +
> +	while ((offset < n_bytes) && sg_miter_next(&miter)) {
> +		len = min(miter.length, n_bytes - offset);
> +		memset(miter.addr, val, len);
> +		offset += len;
> +	}
> +fini:
> +	sg_miter_stop(&miter);
> +	return offset;
> +}
> +EXPORT_SYMBOL(sgl_memset);
> +
> 

Reviewed-by: Bodo Stroesser <bostroesser@gmail.com>