block/qcow2-cache.c - qemu - Git at Google

 /*
  * 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;
     bool                    writethrough;
 };

 Qcow2Cache *qcow2_cache_create(BlockDriverState *bs, int num_tables,
     bool writethrough)
 {
     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);
     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);
     }

     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);

     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;
 }

 bool qcow2_cache_set_writethrough(BlockDriverState *bs, Qcow2Cache *c,
     bool enable)
 {
     bool old = c->writethrough;

     if (!old && enable) {
         qcow2_cache_flush(bs, c);
     }

     c->writethrough = enable;
     return old;
 }
	/*
	* 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;
	bool writethrough;
	};

	Qcow2Cache qcow2_cache_create(BlockDriverState bs, int num_tables,
	bool writethrough)
	{
	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);
	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);
	}

	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);

	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;
	}

	bool qcow2_cache_set_writethrough(BlockDriverState bs, Qcow2Cache c,
	bool enable)
	{
	bool old = c->writethrough;

	if (!old && enable) {
	qcow2_cache_flush(bs, c);
	}

	c->writethrough = enable;
	return old;
	}