SG: Move functions to lib/scatterlist.c and add sg chaining allocator…

… helpers

Manually doing chained sg lists is not trivial, so add some helpers
to make sure that drivers get it right.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

include/linux/scatterlist.h

@@ -7,6 +7,12 @@
 #include <linux/string.h>
 #include <asm/io.h>
 
+struct sg_table {
+	struct scatterlist *sgl;	/* the list */
+	unsigned int nents;		/* number of mapped entries */
+	unsigned int orig_nents;	/* original size of list */
+};
+
 /*
  * Notes on SG table design.
  *
@@ -106,71 +112,12 @@ 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));
 }
 
-/**
- * sg_next - return the next scatterlist entry in a list
- * @sg:		The current sg entry
- *
- * 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.
- *
- **/
-static inline struct scatterlist *sg_next(struct scatterlist *sg)
-{
-#ifdef CONFIG_DEBUG_SG
-	BUG_ON(sg->sg_magic != SG_MAGIC);
-#endif
-	if (sg_is_last(sg))
-		return NULL;
-
-	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
  */
 #define for_each_sg(sglist, sg, nr, __i)	\
 	for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
 
-/**
- * sg_last - return the last scatterlist entry in a list
- * @sgl:	First entry in the scatterlist
- * @nents:	Number of entries in the scatterlist
- *
- * 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@.
- *
- **/
-static inline struct scatterlist *sg_last(struct scatterlist *sgl,
-					  unsigned int nents)
-{
-#ifndef ARCH_HAS_SG_CHAIN
-	struct scatterlist *ret = &sgl[nents - 1];
-#else
-	struct scatterlist *sg, *ret = NULL;
-	unsigned int i;
-
-	for_each_sg(sgl, sg, nents, i)
-		ret = sg;
-
-#endif
-#ifdef CONFIG_DEBUG_SG
-	BUG_ON(sgl[0].sg_magic != SG_MAGIC);
-	BUG_ON(!sg_is_last(ret));
-#endif
-	return ret;
-}
-
 /**
  * sg_chain - Chain two sglists together
  * @prv:	First scatterlist
@@ -222,47 +169,6 @@ static inline void sg_mark_end(struct scatterlist *sg)
 	sg->page_link &= ~0x01;
 }
 
-/**
- * sg_init_table - Initialize SG table
- * @sgl:	   The SG table
- * @nents:	   Number of entries in table
- *
- * Notes:
- *   If this is part of a chained sg table, sg_mark_end() should be
- *   used only on the last table part.
- *
- **/
-static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
-{
-	memset(sgl, 0, sizeof(*sgl) * nents);
-#ifdef CONFIG_DEBUG_SG
-	{
-		unsigned int i;
-		for (i = 0; i < nents; i++)
-			sgl[i].sg_magic = SG_MAGIC;
-	}
-#endif
-	sg_mark_end(&sgl[nents - 1]);
-}
-
-/**
- * sg_init_one - Initialize a single entry sg list
- * @sg:		 SG entry
- * @buf:	 Virtual address for IO
- * @buflen:	 IO length
- *
- * Notes:
- *   This should not be used on a single entry that is part of a larger
- *   table. Use sg_init_table() for that.
- *
- **/
-static inline void sg_init_one(struct scatterlist *sg, const void *buf,
-			       unsigned int buflen)
-{
-	sg_init_table(sg, 1);
-	sg_set_buf(sg, buf, buflen);
-}
-
 /**
  * sg_phys - Return physical address of an sg entry
  * @sg:	     SG entry
@@ -293,4 +199,23 @@ static inline void *sg_virt(struct scatterlist *sg)
 	return page_address(sg_page(sg)) + sg->offset;
 }
 
+struct scatterlist *sg_next(struct scatterlist *);
+struct scatterlist *sg_last(struct scatterlist *s, unsigned int);
+void sg_init_table(struct scatterlist *, unsigned int);
+void sg_init_one(struct scatterlist *, const void *, unsigned int);
+
+typedef struct scatterlist *(sg_alloc_fn)(unsigned int, gfp_t);
+typedef void (sg_free_fn)(struct scatterlist *, unsigned int);
+
+void __sg_free_table(struct sg_table *, sg_free_fn *);
+void sg_free_table(struct sg_table *);
+int __sg_alloc_table(struct sg_table *, unsigned int, gfp_t, sg_alloc_fn *);
+int sg_alloc_table(struct sg_table *, unsigned int, gfp_t);
+
+/*
+ * Maximum number of entries that will be allocated in one piece, if
+ * a list larger than this is required then chaining will be utilized.
+ */
+#define SG_MAX_SINGLE_ALLOC		(PAGE_SIZE / sizeof(struct scatterlist))
+
 #endif /* _LINUX_SCATTERLIST_H */

lib/Makefile

@@ -6,7 +6,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
 	 rbtree.o radix-tree.o dump_stack.o \
 	 idr.o int_sqrt.o extable.o prio_tree.o \
 	 sha1.o irq_regs.o reciprocal_div.o argv_split.o \
-	 proportions.o prio_heap.o
+	 proportions.o prio_heap.o scatterlist.o
 
 lib-$(CONFIG_MMU) += ioremap.o
 lib-$(CONFIG_SMP) += cpumask.o