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