aboutsummaryrefslogtreecommitdiff
path: root/block/qcow2-cache.c
diff options
context:
space:
mode:
Diffstat (limited to 'block/qcow2-cache.c')
-rw-r--r--block/qcow2-cache.c290
1 files changed, 290 insertions, 0 deletions
diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
new file mode 100644
index 0000000000..f7c4e2af0d
--- /dev/null
+++ b/block/qcow2-cache.c
@@ -0,0 +1,290 @@
+/*
+ * L2/refcount table cache for the QCOW2 format
+ *
+ * Copyright (c) 2010 Kevin Wolf <kwolf@redhat.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "block_int.h"
+#include "qemu-common.h"
+#include "qcow2.h"
+
+typedef struct Qcow2CachedTable {
+ void* table;
+ int64_t offset;
+ bool dirty;
+ int cache_hits;
+ int ref;
+} Qcow2CachedTable;
+
+struct Qcow2Cache {
+ int size;
+ Qcow2CachedTable* entries;
+ struct Qcow2Cache* depends;
+ bool writethrough;
+};
+
+Qcow2Cache *qcow2_cache_create(BlockDriverState *bs, int num_tables,
+ bool writethrough)
+{
+ BDRVQcowState *s = bs->opaque;
+ Qcow2Cache *c;
+ int i;
+
+ c = qemu_mallocz(sizeof(*c));
+ c->size = num_tables;
+ c->entries = qemu_mallocz(sizeof(*c->entries) * num_tables);
+ c->writethrough = writethrough;
+
+ for (i = 0; i < c->size; i++) {
+ c->entries[i].table = qemu_blockalign(bs, s->cluster_size);
+ }
+
+ return c;
+}
+
+int qcow2_cache_destroy(BlockDriverState* bs, Qcow2Cache *c)
+{
+ int i;
+
+ for (i = 0; i < c->size; i++) {
+ assert(c->entries[i].ref == 0);
+ qemu_vfree(c->entries[i].table);
+ }
+
+ qemu_free(c->entries);
+ qemu_free(c);
+
+ return 0;
+}
+
+static int qcow2_cache_flush_dependency(BlockDriverState *bs, Qcow2Cache *c)
+{
+ int ret;
+
+ ret = qcow2_cache_flush(bs, c->depends);
+ if (ret < 0) {
+ return ret;
+ }
+
+ c->depends = NULL;
+ return 0;
+}
+
+static int qcow2_cache_entry_flush(BlockDriverState *bs, Qcow2Cache *c, int i)
+{
+ BDRVQcowState *s = bs->opaque;
+ int ret;
+
+ if (!c->entries[i].dirty || !c->entries[i].offset) {
+ return 0;
+ }
+
+ if (c->depends) {
+ ret = qcow2_cache_flush_dependency(bs, c);
+ if (ret < 0) {
+ return ret;
+ }
+ }
+
+ ret = bdrv_pwrite(bs->file, c->entries[i].offset, c->entries[i].table,
+ s->cluster_size);
+ if (ret < 0) {
+ return ret;
+ }
+
+ c->entries[i].dirty = false;
+
+ return 0;
+}
+
+int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c)
+{
+ int result = 0;
+ int ret;
+ int i;
+
+ for (i = 0; i < c->size; i++) {
+ ret = qcow2_cache_entry_flush(bs, c, i);
+ if (ret < 0 && result != -ENOSPC) {
+ result = ret;
+ }
+ }
+
+ if (result == 0) {
+ ret = bdrv_flush(bs->file);
+ if (ret < 0) {
+ result = ret;
+ }
+ }
+
+ return result;
+}
+
+int qcow2_cache_set_dependency(BlockDriverState *bs, Qcow2Cache *c,
+ Qcow2Cache *dependency)
+{
+ int ret;
+
+ if (dependency->depends) {
+ ret = qcow2_cache_flush_dependency(bs, dependency);
+ if (ret < 0) {
+ return ret;
+ }
+ }
+
+ if (c->depends && (c->depends != dependency)) {
+ ret = qcow2_cache_flush_dependency(bs, c);
+ if (ret < 0) {
+ return ret;
+ }
+ }
+
+ c->depends = dependency;
+ return 0;
+}
+
+static int qcow2_cache_find_entry_to_replace(Qcow2Cache *c)
+{
+ int i;
+ int min_count = INT_MAX;
+ int min_index = -1;
+
+
+ for (i = 0; i < c->size; i++) {
+ if (c->entries[i].ref) {
+ continue;
+ }
+
+ if (c->entries[i].cache_hits < min_count) {
+ min_index = i;
+ min_count = c->entries[i].cache_hits;
+ }
+
+ /* Give newer hits priority */
+ /* TODO Check how to optimize the replacement strategy */
+ c->entries[i].cache_hits /= 2;
+ }
+
+ if (min_index == -1) {
+ /* This can't happen in current synchronous code, but leave the check
+ * here as a reminder for whoever starts using AIO with the cache */
+ abort();
+ }
+ return min_index;
+}
+
+static int qcow2_cache_do_get(BlockDriverState *bs, Qcow2Cache *c,
+ uint64_t offset, void **table, bool read_from_disk)
+{
+ BDRVQcowState *s = bs->opaque;
+ int i;
+ int ret;
+
+ /* Check if the table is already cached */
+ for (i = 0; i < c->size; i++) {
+ if (c->entries[i].offset == offset) {
+ goto found;
+ }
+ }
+
+ /* If not, write a table back and replace it */
+ i = qcow2_cache_find_entry_to_replace(c);
+ if (i < 0) {
+ return i;
+ }
+
+ ret = qcow2_cache_entry_flush(bs, c, i);
+ if (ret < 0) {
+ return ret;
+ }
+
+ c->entries[i].offset = 0;
+ if (read_from_disk) {
+ ret = bdrv_pread(bs->file, offset, c->entries[i].table, s->cluster_size);
+ if (ret < 0) {
+ return ret;
+ }
+ }
+
+ /* Give the table some hits for the start so that it won't be replaced
+ * immediately. The number 32 is completely arbitrary. */
+ c->entries[i].cache_hits = 32;
+ c->entries[i].offset = offset;
+
+ /* And return the right table */
+found:
+ c->entries[i].cache_hits++;
+ c->entries[i].ref++;
+ *table = c->entries[i].table;
+ return 0;
+}
+
+int qcow2_cache_get(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
+ void **table)
+{
+ return qcow2_cache_do_get(bs, c, offset, table, true);
+}
+
+int qcow2_cache_get_empty(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
+ void **table)
+{
+ return qcow2_cache_do_get(bs, c, offset, table, false);
+}
+
+int qcow2_cache_put(BlockDriverState *bs, Qcow2Cache *c, void **table)
+{
+ int i;
+
+ for (i = 0; i < c->size; i++) {
+ if (c->entries[i].table == *table) {
+ goto found;
+ }
+ }
+ return -ENOENT;
+
+found:
+ c->entries[i].ref--;
+ *table = NULL;
+
+ assert(c->entries[i].ref >= 0);
+
+ if (c->writethrough) {
+ return qcow2_cache_entry_flush(bs, c, i);
+ } else {
+ return 0;
+ }
+}
+
+void qcow2_cache_entry_mark_dirty(Qcow2Cache *c, void *table)
+{
+ int i;
+
+ for (i = 0; i < c->size; i++) {
+ if (c->entries[i].table == table) {
+ goto found;
+ }
+ }
+ abort();
+
+found:
+ c->entries[i].dirty = true;
+}
+
generated by cgit v1.2.3 (git 2.26.2) at 2024-12-02 03:07:54 +0000