Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761536AbXEJLm5 (ORCPT ); Thu, 10 May 2007 07:42:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757474AbXEJLlP (ORCPT ); Thu, 10 May 2007 07:41:15 -0400 Received: from brick.kernel.dk ([80.160.20.94]:4888 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758276AbXEJLlJ (ORCPT ); Thu, 10 May 2007 07:41:09 -0400 From: Jens Axboe To: linux-kernel@vger.kernel.org Cc: Jens Axboe Subject: [PATCH 7/12] i386 sg: add support for chaining scatterlists Date: Thu, 10 May 2007 13:40:32 +0200 Message-Id: <11787972373410-git-send-email-jens.axboe@oracle.com> X-Mailer: git-send-email 1.5.2.rc1 In-Reply-To: <11787972373654-git-send-email-jens.axboe@oracle.com> References: <11787972373654-git-send-email-jens.axboe@oracle.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3138 Lines: 100 The core of the patch - allow the last sg element in a scatterlist table to point to the start of a new table. We overload the LSB of the page pointer to indicate whether this is a valid sg entry, or merely a link to the next list. Signed-off-by: Jens Axboe --- include/asm-i386/scatterlist.h | 2 + include/linux/scatterlist.h | 52 ++++++++++++++++++++++++++++++++++++++- 2 files changed, 52 insertions(+), 2 deletions(-) diff --git a/include/asm-i386/scatterlist.h b/include/asm-i386/scatterlist.h index d7e45a8..bd5164a 100644 --- a/include/asm-i386/scatterlist.h +++ b/include/asm-i386/scatterlist.h @@ -10,6 +10,8 @@ struct scatterlist { unsigned int length; }; +#define ARCH_HAS_SG_CHAIN + /* These macros should be used after a pci_map_sg call has been done * to get bus addresses of each of the SG entries and their lengths. * You should only work with the number of sg entries pci_map_sg diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index bed5ab4..fa2dc1c 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -20,8 +20,23 @@ static inline void sg_init_one(struct scatterlist *sg, const void *buf, sg_set_buf(sg, buf, buflen); } -#define sg_next(sg) ((sg) + 1) -#define sg_last(sg, nents) (&(sg[(nents) - 1])) +#define sg_is_chain(sg) ((unsigned long) (sg)->page & 0x01) +#define sg_chain_ptr(sg) \ + ((struct scatterlist *) ((unsigned long) (sg)->page & ~0x01)) + +/* + * We overload the meaning of ->page for sg chaining. If the LSB is + * set, the page member contains a pointer to the next sgtable. + */ +static inline struct scatterlist *sg_next(struct scatterlist *sg) +{ + sg++; + + if (unlikely(sg_is_chain(sg))) + sg = sg_chain_ptr(sg); + + return sg; +} /* * Loop over each sg element, following the pointer to a new list if necessary @@ -29,4 +44,37 @@ static inline void sg_init_one(struct scatterlist *sg, const void *buf, #define for_each_sg(sglist, sg, nr, __i) \ for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg)) +/* + * We could improve this by passing in the maximum size of an sglist, so + * we could jump directly to the last table. That would eliminate this + * (potentially) lengthy scan. + */ +static inline struct scatterlist *sg_last(struct scatterlist *sgl, + unsigned int nents) +{ +#ifdef ARCH_HAS_SG_CHAIN + struct scatterlist *ret = &sgl[nents - 1]; +#else + struct scatterlist *sg, *ret = NULL; + int i; + + for_each_sg(sgl, sg, nents, i) + ret = sg; + +#endif + return ret; +} + +/* + * Chain previous sglist to this one + */ +static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents, + struct scatterlist *sgl) +{ +#ifndef ARCH_HAS_SG_CHAIN + BUG(); +#endif + prv[prv_nents - 1].page = (struct page *) ((unsigned long) sgl | 0x01); +} + #endif /* _LINUX_SCATTERLIST_H */ -- 1.5.2.rc1 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/