1 files changed, 327 insertions, 0 deletions

diff --git a/lib/flex_array.c b/lib/flex_array.c
new file mode 100644
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--- /dev/null
+++ b/lib/flex_array.c
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+/*
+ * 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];
+};
+
+/*
+ * 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 | 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, unsigned int total,
+                                        gfp_t flags)
+{
+        struct flex_array *ret;
+        int max_size = FLEX_ARRAY_NR_BASE_PTRS *
+                                FLEX_ARRAY_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;
+        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 element_nr / FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
+}
+
+/**
+ * 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_offset;
+
+        part_offset = element_nr %
+                                FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
+        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.
+ *
+ * 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 = 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_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 = 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->parts[part_nr];
+                if (!part)
+                        return -EINVAL;
+        }
+        dst = &part->elements[index_inside_part(fa, element_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
+ * @end:        index of last (inclusive) element 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 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
+ * @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.
+ *
+ * Locking must be provided by the caller.
+ */
+void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
+{
+        int part_nr = fa_element_to_part_nr(fa, element_nr);
+        struct flex_array_part *part;
+
+        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 = fa->parts[part_nr];
+                if (!part)
+                        return NULL;
+        }
+        return &part->elements[index_inside_part(fa, element_nr)];
+}
+
+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 (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;
+}