3 files changed, 317 insertions, 1 deletions

diff --git a/include/linux/flex_array.h b/include/linux/flex_array.h
new file mode 100644
index 000000000000..23c1ec79a31b
--- /dev/null
+++ b/include/linux/flex_array.h
@@ -0,0 +1,47 @@
+#ifndef _FLEX_ARRAY_H
+#define _FLEX_ARRAY_H
+
+#include <linux/types.h>
+#include <asm/page.h>
+
+#define FLEX_ARRAY_PART_SIZE PAGE_SIZE
+#define FLEX_ARRAY_BASE_SIZE PAGE_SIZE
+
+struct flex_array_part;
+
+/*
+ * This is meant to replace cases where an array-like
+ * structure has gotten too big to fit into kmalloc()
+ * and the developer is getting tempted to use
+ * vmalloc().
+ */
+
+struct flex_array {
+        union {
+                struct {
+                        int element_size;
+                        int total_nr_elements;
+                        struct flex_array_part *parts[0];
+                };
+                /*
+                 * This little trick makes sure that
+                 * sizeof(flex_array) == PAGE_SIZE
+                 */
+                char padding[FLEX_ARRAY_BASE_SIZE];
+        };
+};
+
+#define FLEX_ARRAY_INIT(size, total) { { {\
+        .element_size = (size),         \
+        .total_nr_elements = (total),   \
+} } }
+
+struct flex_array *flex_array_alloc(int element_size, int total, gfp_t flags);
+int flex_array_prealloc(struct flex_array *fa, int start, int end, gfp_t flags);
+void flex_array_free(struct flex_array *fa);
+void flex_array_free_parts(struct flex_array *fa);
+int flex_array_put(struct flex_array *fa, int element_nr, void *src,
+                gfp_t flags);
+void *flex_array_get(struct flex_array *fa, int element_nr);
+
+#endif /* _FLEX_ARRAY_H */
diff --git a/lib/Makefile b/lib/Makefile
index b6d1857bbf08..2e78277eff9d 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -12,7 +12,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.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 ratelimit.o show_mem.o \
-         is_single_threaded.o plist.o decompress.o
+         is_single_threaded.o plist.o decompress.o flex_array.o
 
 lib-$(CONFIG_MMU) += ioremap.o
 lib-$(CONFIG_SMP) += cpumask.o
diff --git a/lib/flex_array.c b/lib/flex_array.c
new file mode 100644
index 000000000000..0e7894ce8882
--- /dev/null
+++ b/lib/flex_array.c
@@ -0,0 +1,269 @@
+/*
+ * Flexible array managed in PAGE_SIZE parts
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright IBM Corporation, 2009
+ *
+ * Author: Dave Hansen <dave@linux.vnet.ibm.com>
+ */
+
+#include <linux/flex_array.h>
+#include <linux/slab.h>
+#include <linux/stddef.h>
+
+struct flex_array_part {
+        char elements[FLEX_ARRAY_PART_SIZE];
+};
+
+static inline int __elements_per_part(int element_size)
+{
+        return FLEX_ARRAY_PART_SIZE / element_size;
+}
+
+static inline int bytes_left_in_base(void)
+{
+        int element_offset = offsetof(struct flex_array, parts);
+        int bytes_left = FLEX_ARRAY_BASE_SIZE - element_offset;
+        return bytes_left;
+}
+
+static inline int nr_base_part_ptrs(void)
+{
+        return bytes_left_in_base() / sizeof(struct flex_array_part *);
+}
+
+/*
+ * If a user requests an allocation which is small
+ * enough, we may simply use the space in the
+ * flex_array->parts[] array to store the user
+ * data.
+ */
+static inline int elements_fit_in_base(struct flex_array *fa)
+{
+        int data_size = fa->element_size * fa->total_nr_elements;
+        if (data_size <= bytes_left_in_base())
+                return 1;
+        return 0;
+}
+
+/**
+ * flex_array_alloc - allocate a new flexible array
+ * @element_size:       the size of individual elements in the array
+ * @total:              total number of elements that this should hold
+ *
+ * Note: all locking must be provided by the caller.
+ *
+ * @total is used to size internal structures.  If the user ever
+ * accesses any array indexes >=@total, it will produce errors.
+ *
+ * The maximum number of elements is defined as: the number of
+ * elements that can be stored in a page times the number of
+ * page pointers that we can fit in the base structure or (using
+ * integer math):
+ *
+ *      (PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *)
+ *
+ * Here's a table showing example capacities.  Note that the maximum
+ * index that the get/put() functions is just nr_objects-1.   This
+ * basically means that you get 4MB of storage on 32-bit and 2MB on
+ * 64-bit.
+ *
+ *
+ * Element size | Objects | Objects |
+ * PAGE_SIZE=4k |  32-bit |  64-bit |
+ * ---------------------------------|
+ *      1 bytes | 4186112 | 2093056 |
+ *      2 bytes | 2093056 | 1046528 |
+ *      3 bytes | 1395030 |  697515 |
+ *      4 bytes | 1046528 |  523264 |
+ *     32 bytes |  130816 |   65408 |
+ *     33 bytes |  126728 |   63364 |
+ *   2048 bytes |    2044 |    1022 |
+ *   2049 bytes |    1022 |     511 |
+ *       void * | 1046528 |  261632 |
+ *
+ * Since 64-bit pointers are twice the size, we lose half the
+ * capacity in the base structure.  Also note that no effort is made
+ * to efficiently pack objects across page boundaries.
+ */
+struct flex_array *flex_array_alloc(int element_size, int total, gfp_t flags)
+{
+        struct flex_array *ret;
+        int max_size = nr_base_part_ptrs() * __elements_per_part(element_size);
+
+        /* max_size will end up 0 if element_size > PAGE_SIZE */
+        if (total > max_size)
+                return NULL;
+        ret = kzalloc(sizeof(struct flex_array), flags);
+        if (!ret)
+                return NULL;
+        ret->element_size = element_size;
+        ret->total_nr_elements = total;
+        return ret;
+}
+
+static int fa_element_to_part_nr(struct flex_array *fa, int element_nr)
+{
+        return element_nr / __elements_per_part(fa->element_size);
+}
+
+/**
+ * flex_array_free_parts - just free the second-level pages
+ * @src:        address of data to copy into the array
+ * @element_nr: index of the position in which to insert
+ *              the new element.
+ *
+ * This is to be used in cases where the base 'struct flex_array'
+ * has been statically allocated and should not be free.
+ */
+void flex_array_free_parts(struct flex_array *fa)
+{
+        int part_nr;
+        int max_part = nr_base_part_ptrs();
+
+        if (elements_fit_in_base(fa))
+                return;
+        for (part_nr = 0; part_nr < max_part; part_nr++)
+                kfree(fa->parts[part_nr]);
+}
+
+void flex_array_free(struct flex_array *fa)
+{
+        flex_array_free_parts(fa);
+        kfree(fa);
+}
+
+static int fa_index_inside_part(struct flex_array *fa, int element_nr)
+{
+        return element_nr % __elements_per_part(fa->element_size);
+}
+
+static int index_inside_part(struct flex_array *fa, int element_nr)
+{
+        int part_offset = fa_index_inside_part(fa, element_nr);
+        return part_offset * fa->element_size;
+}
+
+static struct flex_array_part *
+__fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
+{
+        struct flex_array_part *part = fa->parts[part_nr];
+        if (!part) {
+                /*
+                 * This leaves the part pages uninitialized
+                 * and with potentially random data, just
+                 * as if the user had kmalloc()'d the whole.
+                 * __GFP_ZERO can be used to zero it.
+                 */
+                part = kmalloc(FLEX_ARRAY_PART_SIZE, flags);
+                if (!part)
+                        return NULL;
+                fa->parts[part_nr] = part;
+        }
+        return part;
+}
+
+/**
+ * flex_array_put - copy data into the array at @element_nr
+ * @src:        address of data to copy into the array
+ * @element_nr: index of the position in which to insert
+ *              the new element.
+ *
+ * Note that this *copies* the contents of @src into
+ * the array.  If you are trying to store an array of
+ * pointers, make sure to pass in &ptr instead of ptr.
+ *
+ * Locking must be provided by the caller.
+ */
+int flex_array_put(struct flex_array *fa, int element_nr, void *src, gfp_t flags)
+{
+        int part_nr = fa_element_to_part_nr(fa, element_nr);
+        struct flex_array_part *part;
+        void *dst;
+
+        if (element_nr >= fa->total_nr_elements)
+                return -ENOSPC;
+        if (elements_fit_in_base(fa))
+                part = (struct flex_array_part *)&fa->parts[0];
+        else
+                part = __fa_get_part(fa, part_nr, flags);
+        if (!part)
+                return -ENOMEM;
+        dst = &part->elements[index_inside_part(fa, element_nr)];
+        memcpy(dst, src, fa->element_size);
+        return 0;
+}
+
+/**
+ * flex_array_prealloc - guarantee that array space exists
+ * @start:      index of first array element for which space is allocated
+ * @end:        index of last (inclusive) element for which space is allocated
+ *
+ * This will guarantee that no future calls to flex_array_put()
+ * will allocate memory.  It can be used if you are expecting to
+ * be holding a lock or in some atomic context while writing
+ * data into the array.
+ *
+ * Locking must be provided by the caller.
+ */
+int flex_array_prealloc(struct flex_array *fa, int start, int end, gfp_t flags)
+{
+        int start_part;
+        int end_part;
+        int part_nr;
+        struct flex_array_part *part;
+
+        if (start >= fa->total_nr_elements || end >= fa->total_nr_elements)
+                return -ENOSPC;
+        if (elements_fit_in_base(fa))
+                return 0;
+        start_part = fa_element_to_part_nr(fa, start);
+        end_part = fa_element_to_part_nr(fa, end);
+        for (part_nr = start_part; part_nr <= end_part; part_nr++) {
+                part = __fa_get_part(fa, part_nr, flags);
+                if (!part)
+                        return -ENOMEM;
+        }
+        return 0;
+}
+
+/**
+ * flex_array_get - pull data back out of the array
+ * @element_nr: index of the element to fetch from the array
+ *
+ * Returns a pointer to the data at index @element_nr.  Note
+ * that this is a copy of the data that was passed in.  If you
+ * are using this to store pointers, you'll get back &ptr.
+ *
+ * Locking must be provided by the caller.
+ */
+void *flex_array_get(struct flex_array *fa, int element_nr)
+{
+        int part_nr = fa_element_to_part_nr(fa, element_nr);
+        struct flex_array_part *part;
+        int index;
+
+        if (element_nr >= fa->total_nr_elements)
+                return NULL;
+        if (!fa->parts[part_nr])
+                return NULL;
+        if (elements_fit_in_base(fa))
+                part = (struct flex_array_part *)&fa->parts[0];
+        else
+                part = fa->parts[part_nr];
+        index = index_inside_part(fa, element_nr);
+        return &part->elements[index_inside_part(fa, element_nr)];
+}