Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758939AbXJ2RHs (ORCPT ); Mon, 29 Oct 2007 13:07:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755045AbXJ2RHj (ORCPT ); Mon, 29 Oct 2007 13:07:39 -0400 Received: from astoria.ccjclearline.com ([64.235.106.9]:41912 "EHLO astoria.ccjclearline.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754736AbXJ2RHi (ORCPT ); Mon, 29 Oct 2007 13:07:38 -0400 Date: Mon, 29 Oct 2007 13:04:02 -0400 (EDT) From: "Robert P. J. Day" X-X-Sender: rpjday@localhost.localdomain To: Linux Kernel Mailing List cc: Jens Axboe , gorcunov@gmail.com Subject: [PATCH] Clean up scatterlist.h and introduce macros for readability. Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - astoria.ccjclearline.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - crashcourse.ca X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5003 Lines: 158 Add some macros to to make the bit manipulation more readable, and expand on some of the documentation. This patch incorporates content from Cyrill Gorcunov as well. Signed-off-by: Robert P. J. Day --- compile-tested with "make defconfig" under i386. (what kernel subsection would this fall under?) diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index 4571231..ae296c0 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -1,10 +1,11 @@ #ifndef _LINUX_SCATTERLIST_H #define _LINUX_SCATTERLIST_H -#include -#include #include #include + +#include +#include #include /* @@ -12,19 +13,36 @@ * * Architectures must provide an unsigned long page_link field in the * scatterlist struct. We use that to place the page pointer AND encode - * information about the sg table as well. The two lower bits are reserved - * for this information. + * information about the sg table as well. The two lower bits (which we + * will call the "mask bits" for future reference) are reserved for this + * information. * - * If bit 0 is set, then the page_link contains a pointer to the next sg - * table list. Otherwise the next entry is at sg + 1. + * If bit 0 is *not* set, then the next sg entry is simply the next one + * consecutively in memory. If, however, bit 0 *is* set, we must still + * go to the next consecutive sg entry in memory, but then we must + * additionally (and immediately) follow that pointer to the next + * sg entry in the list. * * If bit 1 is set, then this sg entry is the last element in a list. * * See sg_next(). - * */ + +/* + * Define macros for the mask bits and associated operations. + */ + +#define SG_CHAIN 0x1 +#define SG_LAST 0x2 +#define SG_MASK 0x3 + +#define sg_is_chain(sg) ((sg)->page_link & SG_CHAIN) +#define sg_is_last(sg) ((sg)->page_link & SG_LAST) +#define sg_chain_ptr(sg) \ + ((struct scatterlist *) ((sg)->page_link & ~SG_MASK)) +#define sg_page(sg) ((struct page *) ((sg)->page_link & ~SG_MASK)) -#define SG_MAGIC 0x87654321 +#define SG_MAGIC 0x87654321 /* only for CONFIG_DEBUG_SG */ /** * sg_assign_page - Assign a given page to an SG entry @@ -38,17 +56,17 @@ **/ static inline void sg_assign_page(struct scatterlist *sg, struct page *page) { - unsigned long page_link = sg->page_link & 0x3; + unsigned long saved_mask_bits = sg->page_link & SG_MASK; /* * In order for the low bit stealing approach to work, pages * must be aligned at a 32-bit boundary as a minimum. */ - BUG_ON((unsigned long) page & 0x03); + BUG_ON((unsigned long) page & SG_MASK); #ifdef CONFIG_DEBUG_SG BUG_ON(sg->sg_magic != SG_MAGIC); #endif - sg->page_link = page_link | (unsigned long) page; + sg->page_link = saved_mask_bits | (unsigned long) page; } /** @@ -73,7 +91,6 @@ static inline void sg_set_page(struct scatterlist *sg, struct page *page, sg->length = len; } -#define sg_page(sg) ((struct page *) ((sg)->page_link & ~0x3)) /** * sg_set_buf - Set sg entry to point at given data @@ -88,15 +105,6 @@ static inline void sg_set_buf(struct scatterlist *sg, const void *buf, sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf)); } -/* - * We overload the LSB of the page pointer to indicate whether it's - * a valid sg entry, or whether it points to the start of a new scatterlist. - * Those low bits are there for everyone! (thanks mason :-) - */ -#define sg_is_chain(sg) ((sg)->page_link & 0x01) -#define sg_is_last(sg) ((sg)->page_link & 0x02) -#define sg_chain_ptr(sg) \ - ((struct scatterlist *) ((sg)->page_link & ~0x03)) /** * sg_next - return the next scatterlist entry in a list @@ -179,7 +187,7 @@ static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents, #ifndef ARCH_HAS_SG_CHAIN BUG(); #endif - prv[prv_nents - 1].page_link = (unsigned long) sgl | 0x01; + prv[prv_nents - 1].page_link = (unsigned long) sgl | SG_CHAIN; } /** @@ -193,12 +201,12 @@ static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents, **/ static inline void sg_mark_end(struct scatterlist *sgl, unsigned int nents) { - sgl[nents - 1].page_link = 0x02; + sgl[nents - 1].page_link = SG_LAST; } static inline void __sg_mark_end(struct scatterlist *sg) { - sg->page_link |= 0x02; + sg->page_link |= SG_LAST; } /** -- ======================================================================== Robert P. J. Day Linux Consulting, Training and Annoying Kernel Pedantry Waterloo, Ontario, CANADA http://crashcourse.ca ======================================================================== - 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/