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>

2 files changed, 282 insertions, 1 deletions

diff --git a/lib/Makefile b/lib/Makefile
index b6793ed28d84..89841dc9d91c 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 000000000000..02aaa27e010e
--- /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);