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SubjectRe: [PATCH v3 4/4] scatterlist: add sgl_memset()
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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>

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