summaryrefslogtreecommitdiff
path: root/lib/flex_array.c
diff options
context:
space:
mode:
Diffstat (limited to 'lib/flex_array.c')
-rw-r--r--lib/flex_array.c268
1 files changed, 268 insertions, 0 deletions
diff --git a/lib/flex_array.c b/lib/flex_array.c
new file mode 100644
index 00000000000..7baed2fc3bc
--- /dev/null
+++ b/lib/flex_array.c
@@ -0,0 +1,268 @@
+/*
+ * 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, unsigned 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,
+ unsigned int element_nr)
+{
+ return element_nr / __elements_per_part(fa->element_size);
+}
+
+/**
+ * flex_array_free_parts - just free the second-level pages
+ *
+ * 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 unsigned int index_inside_part(struct flex_array *fa,
+ unsigned int element_nr)
+{
+ unsigned int part_offset;
+
+ part_offset = element_nr % __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) {
+ /*
+ * 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, 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_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, 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
+ * @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)];
+}