qemu/block/qcow2-cache.c

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/*
* 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"
#include "trace.h"
typedef struct Qcow2CachedTable {
void* table;
int64_t offset;
bool dirty;
int cache_hits;
int ref;
} Qcow2CachedTable;
struct Qcow2Cache {
Qcow2CachedTable* entries;
struct Qcow2Cache* depends;
int size;
bool depends_on_flush;
};
Qcow2Cache *qcow2_cache_create(BlockDriverState *bs, int num_tables)
{
BDRVQcowState *s = bs->opaque;
Qcow2Cache *c;
int i;
c = g_malloc0(sizeof(*c));
c->size = num_tables;
c->entries = g_malloc0(sizeof(*c->entries) * num_tables);
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);
}
g_free(c->entries);
g_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;
c->depends_on_flush = false;
return 0;
}
static int qcow2_cache_entry_flush(BlockDriverState *bs, Qcow2Cache *c, int i)
{
BDRVQcowState *s = bs->opaque;
int ret = 0;
if (!c->entries[i].dirty || !c->entries[i].offset) {
return 0;
}
trace_qcow2_cache_entry_flush(qemu_coroutine_self(),
c == s->l2_table_cache, i);
if (c->depends) {
ret = qcow2_cache_flush_dependency(bs, c);
} else if (c->depends_on_flush) {
ret = bdrv_flush(bs->file);
if (ret >= 0) {
c->depends_on_flush = false;
}
}
if (ret < 0) {
return ret;
}
if (c == s->refcount_block_cache) {
BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_UPDATE_PART);
} else if (c == s->l2_table_cache) {
BLKDBG_EVENT(bs->file, BLKDBG_L2_UPDATE);
}
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)
{
BDRVQcowState *s = bs->opaque;
int result = 0;
int ret;
int i;
trace_qcow2_cache_flush(qemu_coroutine_self(), c == s->l2_table_cache);
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;
}
void qcow2_cache_depends_on_flush(Qcow2Cache *c)
{
c->depends_on_flush = true;
}
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;
trace_qcow2_cache_get(qemu_coroutine_self(), c == s->l2_table_cache,
offset, read_from_disk);
/* 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);
trace_qcow2_cache_get_replace_entry(qemu_coroutine_self(),
c == s->l2_table_cache, i);
if (i < 0) {
return i;
}
ret = qcow2_cache_entry_flush(bs, c, i);
if (ret < 0) {
return ret;
}
trace_qcow2_cache_get_read(qemu_coroutine_self(),
c == s->l2_table_cache, i);
c->entries[i].offset = 0;
if (read_from_disk) {
if (c == s->l2_table_cache) {
BLKDBG_EVENT(bs->file, BLKDBG_L2_LOAD);
}
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;
trace_qcow2_cache_get_done(qemu_coroutine_self(),
c == s->l2_table_cache, i);
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);
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;
}