[PATCH 1/3] SG: Move functions to lib/scatterlist.c and add sg chaining allocator helpers

Boaz Harrosh
2007-12-20T14:01:05Z

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 | 125 ++++---------------
lib/Makefile | 2 +-
lib/scatterlist.c | 281 +++++++++++++++++++++++++++++++++++++++++++
3 files changed, 307 insertions(+), 101 deletions(-)
create mode 100644 lib/scatterlist.c

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 416e000..c3ca848 100644
--- a/include/linux/scatterlist.h
+++ b/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.
*
@@ -106,31 +112,6 @@ 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));
}

-/**
- * 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
*/
@@ -138,40 +119,6 @@ static inline struct scatterlist *sg_next(struct scatterlist *sg)
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
* @prv_nents: Number of entries in prv
@@ -223,47 +170,6 @@ static inline void sg_mark_end(struct scatterlist *sg)
}

/**
- * 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 */
diff --git a/lib/Makefile b/lib/Makefile
index b6793ed..89841dc 100644
--- a/lib/Makefile
+++ b/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
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
new file mode 100644
index 0000000..02aaa27
--- /dev/null
+++ b/lib/scatterlist.c
@@ -0,0 +1,281 @@
+/*
+ * Copyright (C) 2007 Jens Axboe <jens.axboe@oracle.com>
+ *
+ * Scatterlist handling helpers.
+ *
+ * This source code is licensed under the GNU General Public License,
+ * Version 2. See the file COPYING for more details.
+ */
+#include <linux/module.h>
+#include <linux/scatterlist.h>
+
+/**
+ * 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.
+ *
+ **/
+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;
+}
+EXPORT_SYMBOL(sg_next);
+
+/**
+ * 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) scans 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@.
+ *
+ **/
+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;
+}
+EXPORT_SYMBOL(sg_last);
+
+/**
+ * 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.
+ *
+ **/
+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]);
+}
+EXPORT_SYMBOL(sg_init_table);
+
+/**
+ * sg_init_one - Initialize a single entry sg list
+ * @sg: SG entry
+ * @buf: Virtual address for IO
+ * @buflen: IO length
+ *
+ **/
+void sg_init_one(struct scatterlist *sg, const void *buf, unsigned int buflen)
+{
+ sg_init_table(sg, 1);
+ sg_set_buf(sg, buf, buflen);
+}
+EXPORT_SYMBOL(sg_init_one);
+
+/*
+ * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
+ * helpers.
+ */
+static struct scatterlist *sg_kmalloc(unsigned int nents, gfp_t gfp_mask)
+{
+ if (nents == SG_MAX_SINGLE_ALLOC)
+ return (struct scatterlist *) __get_free_page(gfp_mask);
+ else
+ return kmalloc(nents * sizeof(struct scatterlist), gfp_mask);
+}
+
+static void sg_kfree(struct scatterlist *sg, unsigned int nents)
+{
+ if (nents == SG_MAX_SINGLE_ALLOC)
+ free_page((unsigned long) sg);
+ else
+ kfree(sg);
+}
+
+/**
+ * __sg_free_table - Free a previously mapped sg table
+ * @table: The sg table header to use
+ * @free_fn: Free function
+ *
+ * Description:
+ * Free an sg table previously allocated and setup with __sg_alloc_table().
+ *
+ **/
+void __sg_free_table(struct sg_table *table, sg_free_fn *free_fn)
+{
+ struct scatterlist *sgl, *next;
+
+ if (unlikely(!table->sgl))
+ return;
+
+ sgl = table->sgl;
+ while (table->orig_nents) {
+ unsigned int alloc_size = table->orig_nents;
+ unsigned int sg_size;
+
+ /*
+ * If we have more than SG_MAX_SINGLE_ALLOC segments left,
+ * then assign 'next' to the sg table after the current one.
+ * sg_size is then one less than alloc size, since the last
+ * element is the chain pointer.
+ */
+ if (alloc_size > SG_MAX_SINGLE_ALLOC) {
+ next = sg_chain_ptr(&sgl[SG_MAX_SINGLE_ALLOC - 1]);
+ alloc_size = SG_MAX_SINGLE_ALLOC;
+ sg_size = alloc_size - 1;
+ } else {
+ sg_size = alloc_size;
+ next = NULL;
+ }
+
+ table->orig_nents -= sg_size;
+ free_fn(sgl, alloc_size);
+ sgl = next;
+ }
+
+ table->sgl = NULL;
+}
+EXPORT_SYMBOL(__sg_free_table);
+
+/**
+ * sg_free_table - Free a previously allocated sg table
+ * @table: The mapped sg table header
+ *
+ **/
+void sg_free_table(struct sg_table *table)
+{
+ __sg_free_table(table, sg_kfree);
+}
+EXPORT_SYMBOL(sg_free_table);
+
+/**
+ * __sg_alloc_table - Allocate and initialize an sg table with given allocator
+ * @table: The sg table header to use
+ * @nents: Number of entries in sg list
+ * @gfp_mask: GFP allocation mask
+ * @alloc_fn: Allocator to use
+ *
+ * Notes:
+ * If this function returns non-0 (eg failure), the caller must call
+ * __sg_free_table() to cleanup any leftover allocations.
+ *
+ **/
+int __sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask,
+ sg_alloc_fn *alloc_fn)
+{
+ struct scatterlist *sg, *prv;
+ unsigned int left;
+
+#ifndef ARCH_HAS_SG_CHAIN
+ BUG_ON(nents > SG_MAX_SINGLE_ALLOC);
+#endif
+
+ memset(table, 0, sizeof(*table));
+
+ left = nents;
+ prv = NULL;
+ do {
+ unsigned int sg_size, alloc_size = left;
+
+ if (alloc_size > SG_MAX_SINGLE_ALLOC) {
+ alloc_size = SG_MAX_SINGLE_ALLOC;
+ sg_size = alloc_size - 1;
+ } else
+ sg_size = alloc_size;
+
+ left -= sg_size;
+
+ sg = alloc_fn(alloc_size, gfp_mask);
+ if (unlikely(!sg))
+ return -ENOMEM;
+
+ sg_init_table(sg, alloc_size);
+ table->nents = table->orig_nents += sg_size;
+
+ /*
+ * If this is the first mapping, assign the sg table header.
+ * If this is not the first mapping, chain previous part.
+ */
+ if (prv)
+ sg_chain(prv, SG_MAX_SINGLE_ALLOC, sg);
+ else
+ table->sgl = sg;
+
+ /*
+ * If no more entries after this one, mark the end
+ */
+ if (!left)
+ sg_mark_end(&sg[sg_size - 1]);
+
+ /*
+ * only really needed for mempool backed sg allocations (like
+ * SCSI), a possible improvement here would be to pass the
+ * table pointer into the allocator and let that clear these
+ * flags
+ */
+ gfp_mask &= ~__GFP_WAIT;
+ gfp_mask |= __GFP_HIGH;
+ prv = sg;
+ } while (left);
+
+ return 0;
+}
+EXPORT_SYMBOL(__sg_alloc_table);
+
+/**
+ * sg_alloc_table - Allocate and initialize an sg table
+ * @table: The sg table header to use
+ * @nents: Number of entries in sg list
+ * @gfp_mask: GFP allocation mask
+ *
+ * Description:
+ * Allocate and initialize an sg table. If @nents@ is larger than
+ * SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
+ *
+ **/
+int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
+{
+ int ret;
+
+ ret = __sg_alloc_table(table, nents, gfp_mask, sg_kmalloc);
+ if (unlikely(ret))
+ __sg_free_table(table, sg_kfree);
+
+ return ret;
+}
+EXPORT_SYMBOL(sg_alloc_table);
--
1.5.3.3