--- /dev/null
+#include <linux/version.h>
+
+#if LINUX_VERSION_CODE < KERNEL_VERSION(3,0,0)
+
+/*
+ * 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>
+#include <linux/module.h>
+#include <linux/reciprocal_div.h>
+
+struct flex_array_part {
+ char elements[FLEX_ARRAY_PART_SIZE];
+};
+
+/*
+ * 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 <= FLEX_ARRAY_BASE_BYTES_LEFT)
+ 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
+ * @flags: page allocation flags to use for base array
+ *
+ * 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 | 4177920 | 2088960 |
+ * 2 bytes | 2088960 | 1044480 |
+ * 3 bytes | 1392300 | 696150 |
+ * 4 bytes | 1044480 | 522240 |
+ * 32 bytes | 130560 | 65408 |
+ * 33 bytes | 126480 | 63240 |
+ * 2048 bytes | 2040 | 1020 |
+ * 2049 bytes | 1020 | 510 |
+ * void * | 1044480 | 261120 |
+ *
+ * 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, unsigned int total,
+ gfp_t flags)
+{
+ struct flex_array *ret;
+ int elems_per_part = 0;
+ int reciprocal_elems = 0;
+ int max_size = 0;
+
+ if (element_size) {
+ elems_per_part = FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
+ reciprocal_elems = reciprocal_value(elems_per_part);
+ max_size = FLEX_ARRAY_NR_BASE_PTRS * elems_per_part;
+ }
+
+ /* 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;
+ ret->elems_per_part = elems_per_part;
+ ret->reciprocal_elems = reciprocal_elems;
+ if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
+ memset(&ret->parts[0], FLEX_ARRAY_FREE,
+ FLEX_ARRAY_BASE_BYTES_LEFT);
+ return ret;
+}
+
+static int fa_element_to_part_nr(struct flex_array *fa,
+ unsigned int element_nr)
+{
+ return reciprocal_divide(element_nr, fa->reciprocal_elems);
+}
+
+/**
+ * flex_array_free_parts - just free the second-level pages
+ * @fa: the flex array from which to free parts
+ *
+ * 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;
+
+ if (elements_fit_in_base(fa))
+ return;
+ for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++)
+ kfree(fa->parts[part_nr]);
+}
+
+void flex_array_free(struct flex_array *fa)
+{
+ flex_array_free_parts(fa);
+ kfree(fa);
+}
+
+static unsigned int index_inside_part(struct flex_array *fa,
+ unsigned int element_nr,
+ unsigned int part_nr)
+{
+ unsigned int part_offset;
+
+ part_offset = element_nr - part_nr * fa->elems_per_part;
+ 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) {
+ part = kmalloc(sizeof(struct flex_array_part), flags);
+ if (!part)
+ return NULL;
+ if (!(flags & __GFP_ZERO))
+ memset(part, FLEX_ARRAY_FREE,
+ sizeof(struct flex_array_part));
+ fa->parts[part_nr] = part;
+ }
+ return part;
+}
+
+/**
+ * flex_array_put - copy data into the array at @element_nr
+ * @fa: the flex array to copy data into
+ * @element_nr: index of the position in which to insert
+ * the new element.
+ * @src: address of data to copy into the array
+ * @flags: page allocation flags to use for array expansion
+ *
+ *
+ * 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.
+ * You may instead wish to use the flex_array_put_ptr()
+ * helper function.
+ *
+ * Locking must be provided by the caller.
+ */
+int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
+ gfp_t flags)
+{
+ int part_nr = 0;
+ struct flex_array_part *part;
+ void *dst;
+
+ if (element_nr >= fa->total_nr_elements)
+ return -ENOSPC;
+ if (!fa->element_size)
+ return 0;
+ if (elements_fit_in_base(fa))
+ part = (struct flex_array_part *)&fa->parts[0];
+ else {
+ part_nr = fa_element_to_part_nr(fa, element_nr);
+ part = __fa_get_part(fa, part_nr, flags);
+ if (!part)
+ return -ENOMEM;
+ }
+ dst = &part->elements[index_inside_part(fa, element_nr, part_nr)];
+ memcpy(dst, src, fa->element_size);
+ return 0;
+}
+
+/**
+ * flex_array_clear - clear element in array at @element_nr
+ * @fa: the flex array of the element.
+ * @element_nr: index of the position to clear.
+ *
+ * Locking must be provided by the caller.
+ */
+int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
+{
+ int part_nr = 0;
+ struct flex_array_part *part;
+ void *dst;
+
+ if (element_nr >= fa->total_nr_elements)
+ return -ENOSPC;
+ if (!fa->element_size)
+ return 0;
+ if (elements_fit_in_base(fa))
+ part = (struct flex_array_part *)&fa->parts[0];
+ else {
+ part_nr = fa_element_to_part_nr(fa, element_nr);
+ part = fa->parts[part_nr];
+ if (!part)
+ return -EINVAL;
+ }
+ dst = &part->elements[index_inside_part(fa, element_nr, part_nr)];
+ memset(dst, FLEX_ARRAY_FREE, fa->element_size);
+ return 0;
+}
+
+/**
+ * flex_array_prealloc - guarantee that array space exists
+ * @fa: the flex array for which to preallocate parts
+ * @start: index of first array element for which space is allocated
+ * @nr_elements: number of elements for which space is allocated
+ * @flags: page allocation flags
+ *
+ * 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, unsigned int start,
+ unsigned int nr_elements, gfp_t flags)
+{
+ int start_part;
+ int end_part;
+ int part_nr;
+ unsigned int end;
+ struct flex_array_part *part;
+
+ if (!start && !nr_elements)
+ return 0;
+ if (start >= fa->total_nr_elements)
+ return -ENOSPC;
+ if (!nr_elements)
+ return 0;
+
+ end = start + nr_elements - 1;
+
+ if (end >= fa->total_nr_elements)
+ return -ENOSPC;
+ if (!fa->element_size)
+ return 0;
+ 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
+ * @fa: the flex array from which to extract data
+ * @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. You
+ * may instead wish to use the flex_array_get_ptr helper.
+ *
+ * Locking must be provided by the caller.
+ */
+void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
+{
+ int part_nr = 0;
+ struct flex_array_part *part;
+
+ if (!fa->element_size)
+ return NULL;
+ if (element_nr >= fa->total_nr_elements)
+ return NULL;
+ if (elements_fit_in_base(fa))
+ part = (struct flex_array_part *)&fa->parts[0];
+ else {
+ part_nr = fa_element_to_part_nr(fa, element_nr);
+ part = fa->parts[part_nr];
+ if (!part)
+ return NULL;
+ }
+ return &part->elements[index_inside_part(fa, element_nr, part_nr)];
+}
+
+/**
+ * flex_array_get_ptr - pull a ptr back out of the array
+ * @fa: the flex array from which to extract data
+ * @element_nr: index of the element to fetch from the array
+ *
+ * Returns the pointer placed in the flex array at element_nr using
+ * flex_array_put_ptr(). This function should not be called if the
+ * element in question was not set using the _put_ptr() helper.
+ */
+void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr)
+{
+ void **tmp;
+
+ tmp = flex_array_get(fa, element_nr);
+ if (!tmp)
+ return NULL;
+
+ return *tmp;
+}
+
+static int part_is_free(struct flex_array_part *part)
+{
+ int i;
+
+ for (i = 0; i < sizeof(struct flex_array_part); i++)
+ if (part->elements[i] != FLEX_ARRAY_FREE)
+ return 0;
+ return 1;
+}
+
+/**
+ * flex_array_shrink - free unused second-level pages
+ * @fa: the flex array to shrink
+ *
+ * Frees all second-level pages that consist solely of unused
+ * elements. Returns the number of pages freed.
+ *
+ * Locking must be provided by the caller.
+ */
+int flex_array_shrink(struct flex_array *fa)
+{
+ struct flex_array_part *part;
+ int part_nr;
+ int ret = 0;
+
+ if (!fa->total_nr_elements || !fa->element_size)
+ return 0;
+ if (elements_fit_in_base(fa))
+ return ret;
+ for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
+ part = fa->parts[part_nr];
+ if (!part)
+ continue;
+ if (part_is_free(part)) {
+ fa->parts[part_nr] = NULL;
+ kfree(part);
+ ret++;
+ }
+ }
+ return ret;
+}
+
+#endif /* Linux version < 3.0.0 */
--- /dev/null
+#ifndef __LINUX_FLEX_ARRAY_WRAPPER_H
+#define __LINUX_FLEX_ARRAY_WRAPPER_H
+
+#include <linux/version.h>
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(3,0,0)
+#include_next <linux/flex_array.h>
+#else
+
+#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;
+ int elems_per_part;
+ u32 reciprocal_elems;
+ struct flex_array_part *parts[];
+ };
+ /*
+ * This little trick makes sure that
+ * sizeof(flex_array) == PAGE_SIZE
+ */
+ char padding[FLEX_ARRAY_BASE_SIZE];
+ };
+};
+
+/* Number of bytes left in base struct flex_array, excluding metadata */
+#define FLEX_ARRAY_BASE_BYTES_LEFT \
+ (FLEX_ARRAY_BASE_SIZE - offsetof(struct flex_array, parts))
+
+/* Number of pointers in base to struct flex_array_part pages */
+#define FLEX_ARRAY_NR_BASE_PTRS \
+ (FLEX_ARRAY_BASE_BYTES_LEFT / sizeof(struct flex_array_part *))
+
+/* Number of elements of size that fit in struct flex_array_part */
+#define FLEX_ARRAY_ELEMENTS_PER_PART(size) \
+ (FLEX_ARRAY_PART_SIZE / size)
+
+/*
+ * Defines a statically allocated flex array and ensures its parameters are
+ * valid.
+ */
+#define DEFINE_FLEX_ARRAY(__arrayname, __element_size, __total) \
+ struct flex_array __arrayname = { { { \
+ .element_size = (__element_size), \
+ .total_nr_elements = (__total), \
+ } } }; \
+ static inline void __arrayname##_invalid_parameter(void) \
+ { \
+ BUILD_BUG_ON((__total) > FLEX_ARRAY_NR_BASE_PTRS * \
+ FLEX_ARRAY_ELEMENTS_PER_PART(__element_size)); \
+ }
+
+struct flex_array *flex_array_alloc(int element_size, unsigned int total,
+ gfp_t flags);
+int flex_array_prealloc(struct flex_array *fa, unsigned int start,
+ unsigned int nr_elements, 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, unsigned int element_nr, void *src,
+ gfp_t flags);
+int flex_array_clear(struct flex_array *fa, unsigned int element_nr);
+void *flex_array_get(struct flex_array *fa, unsigned int element_nr);
+int flex_array_shrink(struct flex_array *fa);
+
+#define flex_array_put_ptr(fa, nr, src, gfp) \
+ flex_array_put(fa, nr, (void *)&(src), gfp)
+
+void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr);
+
+#endif /* Linux version < 3.0.0 */
+#endif /* __LINUX_FLEX_ARRAY_WRAPPER_H */
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