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Date: Thu, 06 Jun 2013 16:12:30 +0300
From: Imre Deak <imre.deak@...el.com>
To: Akinobu Mita <akinobu.mita@...il.com>
Cc: linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
Tejun Heo <tj@...nel.org>,
Herbert Xu <herbert@...dor.apana.org.au>,
"David S. Miller" <davem@...emloft.net>,
linux-crypto@...r.kernel.org,
"James E.J. Bottomley" <JBottomley@...allels.com>,
Douglas Gilbert <dgilbert@...erlog.com>,
linux-scsi@...r.kernel.org
Subject: Re: [PATCH 1/3] lib/scatterlist: introduce sg_pcopy_from_buffer()
and sg_pcopy_to_buffer()
On Thu, 2013-06-06 at 21:52 +0900, Akinobu Mita wrote:
> The only difference between sg_pcopy_{from,to}_buffer() and
> sg_copy_{from,to}_buffer() is an additional argument that specifies
> the number of bytes to skip the SG list before copying.
>
> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Imre Deak <imre.deak@...el.com>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: linux-crypto@...r.kernel.org
> Cc: "James E.J. Bottomley" <JBottomley@...allels.com>
> Cc: Douglas Gilbert <dgilbert@...erlog.com>
> Cc: linux-scsi@...r.kernel.org
> ---
> include/linux/scatterlist.h | 5 ++
> lib/scatterlist.c | 109 ++++++++++++++++++++++++++++++++++++--------
> 2 files changed, 94 insertions(+), 20 deletions(-)
>
> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
> index 5951e3f..f5dee42 100644
> --- a/include/linux/scatterlist.h
> +++ b/include/linux/scatterlist.h
> @@ -241,6 +241,11 @@ size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
> size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
> void *buf, size_t buflen);
>
> +size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
> + void *buf, size_t buflen, off_t skip);
> +size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
> + void *buf, size_t buflen, off_t skip);
> +
> /*
> * 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 a1cf8ca..3b40b72 100644
> --- a/lib/scatterlist.c
> +++ b/lib/scatterlist.c
> @@ -453,6 +453,47 @@ void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
> }
> EXPORT_SYMBOL(sg_miter_start);
>
> +static bool sg_miter_get_next_page(struct sg_mapping_iter *miter)
> +{
> + if (!miter->__remaining) {
> + struct scatterlist *sg;
> + unsigned long pgoffset;
> +
> + if (!__sg_page_iter_next(&miter->piter))
> + return false;
> +
> + sg = miter->piter.sg;
> + pgoffset = miter->piter.sg_pgoffset;
> +
> + miter->__offset = pgoffset ? 0 : sg->offset;
> + miter->__remaining = sg->offset + sg->length -
> + (pgoffset << PAGE_SHIFT) - miter->__offset;
> + miter->__remaining = min_t(unsigned long, miter->__remaining,
> + PAGE_SIZE - miter->__offset);
> + }
> +
> + return true;
> +}
> +
> +static bool sg_miter_seek(struct sg_mapping_iter *miter, off_t offset)
> +{
> + WARN_ON(miter->addr);
> +
> + while (offset) {
> + off_t consumed;
> +
> + if (!sg_miter_get_next_page(miter))
> + return false;
> +
> + consumed = min_t(off_t, offset, miter->__remaining);
> + miter->__offset += consumed;
> + miter->__remaining -= consumed;
> + offset -= consumed;
> + }
> +
> + return true;
> +}
> +
> /**
> * sg_miter_next - proceed mapping iterator to the next mapping
> * @miter: sg mapping iter to proceed
> @@ -478,22 +519,9 @@ bool sg_miter_next(struct sg_mapping_iter *miter)
> * Get to the next page if necessary.
> * __remaining, __offset is adjusted by sg_miter_stop
> */
> - if (!miter->__remaining) {
> - struct scatterlist *sg;
> - unsigned long pgoffset;
> -
> - if (!__sg_page_iter_next(&miter->piter))
> - return false;
> -
> - sg = miter->piter.sg;
> - pgoffset = miter->piter.sg_pgoffset;
> + if (!sg_miter_get_next_page(miter))
> + return false;
>
> - miter->__offset = pgoffset ? 0 : sg->offset;
> - miter->__remaining = sg->offset + sg->length -
> - (pgoffset << PAGE_SHIFT) - miter->__offset;
> - miter->__remaining = min_t(unsigned long, miter->__remaining,
> - PAGE_SIZE - miter->__offset);
> - }
> miter->page = sg_page_iter_page(&miter->piter);
> miter->consumed = miter->length = miter->__remaining;
>
> @@ -552,14 +580,16 @@ EXPORT_SYMBOL(sg_miter_stop);
> * @nents: Number of SG entries
> * @buf: Where to copy from
> * @buflen: The number of bytes to copy
> - * @to_buffer: transfer direction (non zero == from an sg list to a
> - * buffer, 0 == from a buffer to an sg list
> + * @skip: Number of bytes to skip before copying
> + * @to_buffer: transfer direction (true == from an sg list to a
> + * buffer, false == from a buffer to an sg list
> *
> * Returns the number of copied bytes.
> *
> **/
> static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
> - void *buf, size_t buflen, int to_buffer)
> + void *buf, size_t buflen, off_t skip,
> + bool to_buffer)
> {
> unsigned int offset = 0;
> struct sg_mapping_iter miter;
> @@ -573,6 +603,9 @@ static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
>
> sg_miter_start(&miter, sgl, nents, sg_flags);
>
> + if (!sg_miter_seek(&miter, skip))
> + return false;
Looks ok to me, perhaps adding the seek functionality to the mapping
iterator would make things more generic and the mapping iterator more
resemble the page iterator. So we'd have a new sg_miter_start_offset and
call it here something like:
sg_miter_start_offset(&miter, sgl, nents, sg_flags, skip);
Just my 2 cents,
Imre
> +
> local_irq_save(flags);
>
> while (sg_miter_next(&miter) && offset < buflen) {
> @@ -607,7 +640,7 @@ static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
> size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
> void *buf, size_t buflen)
> {
> - return sg_copy_buffer(sgl, nents, buf, buflen, 0);
> + return sg_copy_buffer(sgl, nents, buf, buflen, 0, false);
> }
> EXPORT_SYMBOL(sg_copy_from_buffer);
>
> @@ -624,6 +657,42 @@ EXPORT_SYMBOL(sg_copy_from_buffer);
> size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
> void *buf, size_t buflen)
> {
> - return sg_copy_buffer(sgl, nents, buf, buflen, 1);
> + return sg_copy_buffer(sgl, nents, buf, buflen, 0, true);
> }
> EXPORT_SYMBOL(sg_copy_to_buffer);
> +
> +/**
> + * sg_pcopy_from_buffer - Copy from a linear buffer to an SG list
> + * @sgl: The SG list
> + * @nents: Number of SG entries
> + * @buf: Where to copy from
> + * @skip: Number of bytes to skip before copying
> + * @buflen: The number of bytes to copy
> + *
> + * Returns the number of copied bytes.
> + *
> + **/
> +size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
> + void *buf, size_t buflen, off_t skip)
> +{
> + return sg_copy_buffer(sgl, nents, buf, buflen, skip, false);
> +}
> +EXPORT_SYMBOL(sg_pcopy_from_buffer);
> +
> +/**
> + * sg_pcopy_to_buffer - Copy from an SG list to a linear buffer
> + * @sgl: The SG list
> + * @nents: Number of SG entries
> + * @buf: Where to copy to
> + * @skip: Number of bytes to skip before copying
> + * @buflen: The number of bytes to copy
> + *
> + * Returns the number of copied bytes.
> + *
> + **/
> +size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
> + void *buf, size_t buflen, off_t skip)
> +{
> + return sg_copy_buffer(sgl, nents, buf, buflen, skip, true);
> +}
> +EXPORT_SYMBOL(sg_pcopy_to_buffer);
--
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