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Change table chaining layout

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Change the page member of the scatterlist structure to be an unsigned
long, and encode more stuff in the lower bits:

- Bits 0 and 1 zero: this is a normal sg entry. Next sg entry is located
  at sg + 1.
- Bit 0 set: this is a chain entry, the next real entry is at ->page_link
  with the two low bits masked off.
- Bit 1 set: this is the final entry in the sg entry. sg_next() will return
  NULL when passed such an entry.

It's thus important that sg table users use the proper accessors to get
and set the page member.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2007-10-22 19:57:20 +02:00
parent 58b053e4ce
commit 18dabf473e
25 changed files with 79 additions and 49 deletions
Download patch file Download diff file Expand all files Collapse all files

78
include/linux/scatterlist.h
View file

@ -2,9 +2,26 @@
#define _LINUX_SCATTERLIST_H
#include <asm/scatterlist.h>
#include <asm/io.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <asm/io.h>
/*
* Notes on SG table design.
*
* 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.
*
* 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 1 is set, then this sg entry is the last element in a list.
*
* See sg_next().
*
*/
/**
* sg_set_page - Set sg entry to point at given page
@ -20,11 +37,20 @@
**/
static inline void sg_set_page(struct scatterlist *sg, struct page *page)
{
sg->page = page;
unsigned long page_link = sg->page_link & 0x3;
sg->page_link = page_link | (unsigned long) page;
}
#define sg_page(sg) ((sg)->page)
#define sg_page(sg) ((struct page *) ((sg)->page_link & ~0x3))
/**
* sg_set_buf - Set sg entry to point at given data
* @sg: SG entry
* @buf: Data
* @buflen: Data length
*
**/
static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
unsigned int buflen)
{
@ -38,26 +64,27 @@ static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
* 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) ((unsigned long) (sg)->page & 0x01)
#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 *) ((unsigned long) (sg)->page & ~0x01))
((struct scatterlist *) ((sg)->page_link & ~0x03))
/**
* sg_next - return the next scatterlist entry in a list
* @sg: The current sg entry
*
* Usually the next entry will be @sg@ + 1, but if this sg element is part
* of a chained scatterlist, it could jump to the start of a new
* scatterlist array.
* Description:
* Usually the next entry will be @sg@ + 1, but if this sg element is part
* of a chained scatterlist, it could jump to the start of a new
* scatterlist array.
*
* Note that the caller must ensure that there are further entries after
* the current entry, this function will NOT return NULL for an end-of-list.
*
*/
**/
static inline struct scatterlist *sg_next(struct scatterlist *sg)
{
sg++;
if (sg_is_last(sg))
return NULL;
sg++;
if (unlikely(sg_is_chain(sg)))
sg = sg_chain_ptr(sg);
@ -75,14 +102,15 @@ static inline struct scatterlist *sg_next(struct scatterlist *sg)
* @sgl: First entry in the scatterlist
* @nents: Number of entries in the scatterlist
*
* Should only be used casually, it (currently) scan the entire list
* to get the last entry.
* Description:
* Should only be used casually, it (currently) scan the entire list
* to get the last entry.
*
* Note that the @sgl@ pointer passed in need not be the first one,
* the important bit is that @nents@ denotes the number of entries that
* exist from @sgl@.
* Note that the @sgl@ pointer passed in need not be the first one,
* the important bit is that @nents@ denotes the number of entries that
* exist from @sgl@.
*
*/
**/
static inline struct scatterlist *sg_last(struct scatterlist *sgl,
unsigned int nents)
{
@ -105,16 +133,17 @@ static inline struct scatterlist *sg_last(struct scatterlist *sgl,
* @prv_nents: Number of entries in prv
* @sgl: Second scatterlist
*
* Links @prv@ and @sgl@ together, to form a longer scatterlist.
* Description:
* Links @prv@ and @sgl@ together, to form a longer scatterlist.
*
*/
**/
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);
prv[prv_nents - 1].page_link = (unsigned long) sgl | 0x01;
}
/**
@ -128,13 +157,14 @@ 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;
}
static inline void __sg_mark_end(struct scatterlist *sg)
{
sg->page_link |= 0x02;
}
/**
* sg_init_one - Initialize a single entry sg list
* @sg: SG entry
@ -187,7 +217,7 @@ static inline unsigned long sg_phys(struct scatterlist *sg)
/**
* sg_virt - Return virtual address of an sg entry
* @sg: SG entry
* @sg: SG entry
*
* Description:
* This calls page_address() on the page in this sg entry, and adds the