linux-kernel - Re: [PATCH v5 4/4] scatterlist: add sgl

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Date:   Thu, 7 Jan 2021 13:46:29 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Douglas Gilbert <dgilbert@...erlog.com>
Cc:     linux-scsi@...r.kernel.org, linux-block@...r.kernel.org,
        target-devel@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org, martin.petersen@...cle.com,
        jejb@...ux.vnet.ibm.com, bostroesser@...il.com, bvanassche@....org,
        ddiss@...e.de
Subject: Re: [PATCH v5 4/4] scatterlist: add sgl_memset()

On Mon, Dec 28, 2020 at 06:49:55PM -0500, Douglas Gilbert wrote:
> 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.
> 
> Reviewed-by: Bodo Stroesser <bostroesser@...il.com>
> Signed-off-by: Douglas Gilbert <dgilbert@...erlog.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 71be65f9ebb5..70d3f1f73df1 100644
> +++ b/include/linux/scatterlist.h
> @@ -333,6 +333,9 @@ bool sgl_compare_sgl_idx(struct scatterlist *x_sgl, unsigned int x_nents, off_t
>  			 struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip,
>  			 size_t n_bytes, size_t *miscompare_idx);
>  
> +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 9332365e7eb6..f06614a880c8 100644
> +++ b/lib/scatterlist.c
> @@ -1038,26 +1038,7 @@ 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);

May as well make this one liner a static inline in the header. Just
rename this function to sgl_memset so the diff is clearer

Jason