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

 /*
  * Block driver for the QCOW version 2 format
  *
  * Copyright (c) 2004-2006 Fabrice Bellard
  *
  * 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 "qemu-common.h"
 #include "block_int.h"
 #include "block/qcow2.h"

 typedef struct QEMU_PACKED QCowSnapshotHeader {
     /* header is 8 byte aligned */
     uint64_t l1_table_offset;

     uint32_t l1_size;
     uint16_t id_str_size;
     uint16_t name_size;

     uint32_t date_sec;
     uint32_t date_nsec;

     uint64_t vm_clock_nsec;

     uint32_t vm_state_size;
     uint32_t extra_data_size; /* for extension */
     /* extra data follows */
     /* id_str follows */
     /* name follows  */
 } QCowSnapshotHeader;

 void qcow2_free_snapshots(BlockDriverState *bs)
 {
     BDRVQcowState *s = bs->opaque;
     int i;

     for(i = 0; i < s->nb_snapshots; i++) {
         g_free(s->snapshots[i].name);
         g_free(s->snapshots[i].id_str);
     }
     g_free(s->snapshots);
     s->snapshots = NULL;
     s->nb_snapshots = 0;
 }

 int qcow2_read_snapshots(BlockDriverState *bs)
 {
     BDRVQcowState *s = bs->opaque;
     QCowSnapshotHeader h;
     QCowSnapshot *sn;
     int i, id_str_size, name_size;
     int64_t offset;
     uint32_t extra_data_size;

     if (!s->nb_snapshots) {
         s->snapshots = NULL;
         s->snapshots_size = 0;
         return 0;
     }

     offset = s->snapshots_offset;
     s->snapshots = g_malloc0(s->nb_snapshots * sizeof(QCowSnapshot));
     for(i = 0; i < s->nb_snapshots; i++) {
         offset = align_offset(offset, 8);
         if (bdrv_pread(bs->file, offset, &h, sizeof(h)) != sizeof(h))
             goto fail;
         offset += sizeof(h);
         sn = s->snapshots + i;
         sn->l1_table_offset = be64_to_cpu(h.l1_table_offset);
         sn->l1_size = be32_to_cpu(h.l1_size);
         sn->vm_state_size = be32_to_cpu(h.vm_state_size);
         sn->date_sec = be32_to_cpu(h.date_sec);
         sn->date_nsec = be32_to_cpu(h.date_nsec);
         sn->vm_clock_nsec = be64_to_cpu(h.vm_clock_nsec);
         extra_data_size = be32_to_cpu(h.extra_data_size);

         id_str_size = be16_to_cpu(h.id_str_size);
         name_size = be16_to_cpu(h.name_size);

         offset += extra_data_size;

         sn->id_str = g_malloc(id_str_size + 1);
         if (bdrv_pread(bs->file, offset, sn->id_str, id_str_size) != id_str_size)
             goto fail;
         offset += id_str_size;
         sn->id_str[id_str_size] = '\0';

         sn->name = g_malloc(name_size + 1);
         if (bdrv_pread(bs->file, offset, sn->name, name_size) != name_size)
             goto fail;
         offset += name_size;
         sn->name[name_size] = '\0';
     }
     s->snapshots_size = offset - s->snapshots_offset;
     return 0;
  fail:
     qcow2_free_snapshots(bs);
     return -1;
 }

 /* add at the end of the file a new list of snapshots */
 static int qcow2_write_snapshots(BlockDriverState *bs)
 {
     BDRVQcowState *s = bs->opaque;
     QCowSnapshot *sn;
     QCowSnapshotHeader h;
     int i, name_size, id_str_size, snapshots_size;
     uint64_t data64;
     uint32_t data32;
     int64_t offset, snapshots_offset;

     /* compute the size of the snapshots */
     offset = 0;
     for(i = 0; i < s->nb_snapshots; i++) {
         sn = s->snapshots + i;
         offset = align_offset(offset, 8);
         offset += sizeof(h);
         offset += strlen(sn->id_str);
         offset += strlen(sn->name);
     }
     snapshots_size = offset;

     snapshots_offset = qcow2_alloc_clusters(bs, snapshots_size);
     bdrv_flush(bs->file);
     offset = snapshots_offset;
     if (offset < 0) {
         return offset;
     }

     for(i = 0; i < s->nb_snapshots; i++) {
         sn = s->snapshots + i;
         memset(&h, 0, sizeof(h));
         h.l1_table_offset = cpu_to_be64(sn->l1_table_offset);
         h.l1_size = cpu_to_be32(sn->l1_size);
         h.vm_state_size = cpu_to_be32(sn->vm_state_size);
         h.date_sec = cpu_to_be32(sn->date_sec);
         h.date_nsec = cpu_to_be32(sn->date_nsec);
         h.vm_clock_nsec = cpu_to_be64(sn->vm_clock_nsec);

         id_str_size = strlen(sn->id_str);
         name_size = strlen(sn->name);
         h.id_str_size = cpu_to_be16(id_str_size);
         h.name_size = cpu_to_be16(name_size);
         offset = align_offset(offset, 8);
         if (bdrv_pwrite_sync(bs->file, offset, &h, sizeof(h)) < 0)
             goto fail;
         offset += sizeof(h);
         if (bdrv_pwrite_sync(bs->file, offset, sn->id_str, id_str_size) < 0)
             goto fail;
         offset += id_str_size;
         if (bdrv_pwrite_sync(bs->file, offset, sn->name, name_size) < 0)
             goto fail;
         offset += name_size;
     }

     /* update the various header fields */
     data64 = cpu_to_be64(snapshots_offset);
     if (bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, snapshots_offset),
                     &data64, sizeof(data64)) < 0)
         goto fail;
     data32 = cpu_to_be32(s->nb_snapshots);
     if (bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, nb_snapshots),
                     &data32, sizeof(data32)) < 0)
         goto fail;

     /* free the old snapshot table */
     qcow2_free_clusters(bs, s->snapshots_offset, s->snapshots_size);
     s->snapshots_offset = snapshots_offset;
     s->snapshots_size = snapshots_size;
     return 0;
  fail:
     return -1;
 }

 static void find_new_snapshot_id(BlockDriverState *bs,
                                  char *id_str, int id_str_size)
 {
     BDRVQcowState *s = bs->opaque;
     QCowSnapshot *sn;
     int i, id, id_max = 0;

     for(i = 0; i < s->nb_snapshots; i++) {
         sn = s->snapshots + i;
         id = strtoul(sn->id_str, NULL, 10);
         if (id > id_max)
             id_max = id;
     }
     snprintf(id_str, id_str_size, "%d", id_max + 1);
 }

 static int find_snapshot_by_id(BlockDriverState *bs, const char *id_str)
 {
     BDRVQcowState *s = bs->opaque;
     int i;

     for(i = 0; i < s->nb_snapshots; i++) {
         if (!strcmp(s->snapshots[i].id_str, id_str))
             return i;
     }
     return -1;
 }

 static int find_snapshot_by_id_or_name(BlockDriverState *bs, const char *name)
 {
     BDRVQcowState *s = bs->opaque;
     int i, ret;

     ret = find_snapshot_by_id(bs, name);
     if (ret >= 0)
         return ret;
     for(i = 0; i < s->nb_snapshots; i++) {
         if (!strcmp(s->snapshots[i].name, name))
             return i;
     }
     return -1;
 }

 /* if no id is provided, a new one is constructed */
 int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
 {
     BDRVQcowState *s = bs->opaque;
     QCowSnapshot *snapshots1, sn1, *sn = &sn1;
     int i, ret;
     uint64_t *l1_table = NULL;
     int64_t l1_table_offset;

     memset(sn, 0, sizeof(*sn));

     if (sn_info->id_str[0] == '\0') {
         /* compute a new id */
         find_new_snapshot_id(bs, sn_info->id_str, sizeof(sn_info->id_str));
     }

     /* check that the ID is unique */
     if (find_snapshot_by_id(bs, sn_info->id_str) >= 0)
         return -ENOENT;

     sn->id_str = g_strdup(sn_info->id_str);
     if (!sn->id_str)
         goto fail;
     sn->name = g_strdup(sn_info->name);
     if (!sn->name)
         goto fail;
     sn->vm_state_size = sn_info->vm_state_size;
     sn->date_sec = sn_info->date_sec;
     sn->date_nsec = sn_info->date_nsec;
     sn->vm_clock_nsec = sn_info->vm_clock_nsec;

     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1);
     if (ret < 0)
         goto fail;

     /* create the L1 table of the snapshot */
     l1_table_offset = qcow2_alloc_clusters(bs, s->l1_size * sizeof(uint64_t));
     if (l1_table_offset < 0) {
         goto fail;
     }
     bdrv_flush(bs->file);

     sn->l1_table_offset = l1_table_offset;
     sn->l1_size = s->l1_size;

     if (s->l1_size != 0) {
         l1_table = g_malloc(s->l1_size * sizeof(uint64_t));
     } else {
         l1_table = NULL;
     }

     for(i = 0; i < s->l1_size; i++) {
         l1_table[i] = cpu_to_be64(s->l1_table[i]);
     }
     if (bdrv_pwrite_sync(bs->file, sn->l1_table_offset,
                     l1_table, s->l1_size * sizeof(uint64_t)) < 0)
         goto fail;
     g_free(l1_table);
     l1_table = NULL;

     snapshots1 = g_malloc((s->nb_snapshots + 1) * sizeof(QCowSnapshot));
     if (s->snapshots) {
         memcpy(snapshots1, s->snapshots, s->nb_snapshots * sizeof(QCowSnapshot));
         g_free(s->snapshots);
     }
     s->snapshots = snapshots1;
     s->snapshots[s->nb_snapshots++] = *sn;

     if (qcow2_write_snapshots(bs) < 0)
         goto fail;
 #ifdef DEBUG_ALLOC
     {
       BdrvCheckResult result = {0};
       qcow2_check_refcounts(bs, &result);
     }
 #endif
     return 0;
  fail:
     g_free(sn->name);
     g_free(l1_table);
     return -1;
 }

 /* copy the snapshot 'snapshot_name' into the current disk image */
 int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
 {
     BDRVQcowState *s = bs->opaque;
     QCowSnapshot *sn;
     int i, snapshot_index;
     int cur_l1_bytes, sn_l1_bytes;

     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
     if (snapshot_index < 0)
         return -ENOENT;
     sn = &s->snapshots[snapshot_index];

     if (qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, -1) < 0)
         goto fail;

     if (qcow2_grow_l1_table(bs, sn->l1_size, true) < 0)
         goto fail;

     cur_l1_bytes = s->l1_size * sizeof(uint64_t);
     sn_l1_bytes = sn->l1_size * sizeof(uint64_t);

     if (cur_l1_bytes > sn_l1_bytes) {
         memset(s->l1_table + sn->l1_size, 0, cur_l1_bytes - sn_l1_bytes);
     }

     /* copy the snapshot l1 table to the current l1 table */
     if (bdrv_pread(bs->file, sn->l1_table_offset,
                    s->l1_table, sn_l1_bytes) < 0)
         goto fail;
     if (bdrv_pwrite_sync(bs->file, s->l1_table_offset,
                     s->l1_table, cur_l1_bytes) < 0)
         goto fail;
     for(i = 0;i < s->l1_size; i++) {
         be64_to_cpus(&s->l1_table[i]);
     }

     if (qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1) < 0)
         goto fail;

 #ifdef DEBUG_ALLOC
     {
         BdrvCheckResult result = {0};
         qcow2_check_refcounts(bs, &result);
     }
 #endif
     return 0;
  fail:
     return -EIO;
 }

 int qcow2_snapshot_delete(BlockDriverState *bs, const char *snapshot_id)
 {
     BDRVQcowState *s = bs->opaque;
     QCowSnapshot *sn;
     int snapshot_index, ret;

     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
     if (snapshot_index < 0)
         return -ENOENT;
     sn = &s->snapshots[snapshot_index];

     ret = qcow2_update_snapshot_refcount(bs, sn->l1_table_offset, sn->l1_size, -1);
     if (ret < 0)
         return ret;
     /* must update the copied flag on the current cluster offsets */
     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
     if (ret < 0)
         return ret;
     qcow2_free_clusters(bs, sn->l1_table_offset, sn->l1_size * sizeof(uint64_t));

     g_free(sn->id_str);
     g_free(sn->name);
     memmove(sn, sn + 1, (s->nb_snapshots - snapshot_index - 1) * sizeof(*sn));
     s->nb_snapshots--;
     ret = qcow2_write_snapshots(bs);
     if (ret < 0) {
         /* XXX: restore snapshot if error ? */
         return ret;
     }
 #ifdef DEBUG_ALLOC
     {
         BdrvCheckResult result = {0};
         qcow2_check_refcounts(bs, &result);
     }
 #endif
     return 0;
 }

 int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab)
 {
     BDRVQcowState *s = bs->opaque;
     QEMUSnapshotInfo *sn_tab, *sn_info;
     QCowSnapshot *sn;
     int i;

     if (!s->nb_snapshots) {
         *psn_tab = NULL;
         return s->nb_snapshots;
     }

     sn_tab = g_malloc0(s->nb_snapshots * sizeof(QEMUSnapshotInfo));
     for(i = 0; i < s->nb_snapshots; i++) {
         sn_info = sn_tab + i;
         sn = s->snapshots + i;
         pstrcpy(sn_info->id_str, sizeof(sn_info->id_str),
                 sn->id_str);
         pstrcpy(sn_info->name, sizeof(sn_info->name),
                 sn->name);
         sn_info->vm_state_size = sn->vm_state_size;
         sn_info->date_sec = sn->date_sec;
         sn_info->date_nsec = sn->date_nsec;
         sn_info->vm_clock_nsec = sn->vm_clock_nsec;
     }
     *psn_tab = sn_tab;
     return s->nb_snapshots;
 }

 int qcow2_snapshot_load_tmp(BlockDriverState *bs, const char *snapshot_name)
 {
     int i, snapshot_index, l1_size2;
     BDRVQcowState *s = bs->opaque;
     QCowSnapshot *sn;

     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_name);
     if (snapshot_index < 0) {
         return -ENOENT;
     }

     sn = &s->snapshots[snapshot_index];
     s->l1_size = sn->l1_size;
     l1_size2 = s->l1_size * sizeof(uint64_t);
     if (s->l1_table != NULL) {
         g_free(s->l1_table);
     }

     s->l1_table_offset = sn->l1_table_offset;
     s->l1_table = g_malloc0(align_offset(l1_size2, 512));

     if (bdrv_pread(bs->file, sn->l1_table_offset,
                    s->l1_table, l1_size2) != l1_size2) {
         return -1;
     }

     for(i = 0;i < s->l1_size; i++) {
         be64_to_cpus(&s->l1_table[i]);
     }
     return 0;
 }
	/*
	* Block driver for the QCOW version 2 format
	*
	* Copyright (c) 2004-2006 Fabrice Bellard
	*
	* 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 "qemu-common.h"
	#include "block_int.h"
	#include "block/qcow2.h"

	typedef struct QEMU_PACKED QCowSnapshotHeader {
	/* header is 8 byte aligned */
	uint64_t l1_table_offset;

	uint32_t l1_size;
	uint16_t id_str_size;
	uint16_t name_size;

	uint32_t date_sec;
	uint32_t date_nsec;

	uint64_t vm_clock_nsec;

	uint32_t vm_state_size;
	uint32_t extra_data_size; /* for extension */
	/* extra data follows */
	/* id_str follows */
	/* name follows */
	} QCowSnapshotHeader;

	void qcow2_free_snapshots(BlockDriverState *bs)
	{
	BDRVQcowState *s = bs->opaque;
	int i;

	for(i = 0; i < s->nb_snapshots; i++) {
	g_free(s->snapshots[i].name);
	g_free(s->snapshots[i].id_str);
	}
	g_free(s->snapshots);
	s->snapshots = NULL;
	s->nb_snapshots = 0;
	}

	int qcow2_read_snapshots(BlockDriverState *bs)
	{
	BDRVQcowState *s = bs->opaque;
	QCowSnapshotHeader h;
	QCowSnapshot *sn;
	int i, id_str_size, name_size;
	int64_t offset;
	uint32_t extra_data_size;

	if (!s->nb_snapshots) {
	s->snapshots = NULL;
	s->snapshots_size = 0;
	return 0;
	}

	offset = s->snapshots_offset;
	s->snapshots = g_malloc0(s->nb_snapshots * sizeof(QCowSnapshot));
	for(i = 0; i < s->nb_snapshots; i++) {
	offset = align_offset(offset, 8);
	if (bdrv_pread(bs->file, offset, &h, sizeof(h)) != sizeof(h))
	goto fail;
	offset += sizeof(h);
	sn = s->snapshots + i;
	sn->l1_table_offset = be64_to_cpu(h.l1_table_offset);
	sn->l1_size = be32_to_cpu(h.l1_size);
	sn->vm_state_size = be32_to_cpu(h.vm_state_size);
	sn->date_sec = be32_to_cpu(h.date_sec);
	sn->date_nsec = be32_to_cpu(h.date_nsec);
	sn->vm_clock_nsec = be64_to_cpu(h.vm_clock_nsec);
	extra_data_size = be32_to_cpu(h.extra_data_size);

	id_str_size = be16_to_cpu(h.id_str_size);
	name_size = be16_to_cpu(h.name_size);

	offset += extra_data_size;

	sn->id_str = g_malloc(id_str_size + 1);
	if (bdrv_pread(bs->file, offset, sn->id_str, id_str_size) != id_str_size)
	goto fail;
	offset += id_str_size;
	sn->id_str[id_str_size] = '\0';

	sn->name = g_malloc(name_size + 1);
	if (bdrv_pread(bs->file, offset, sn->name, name_size) != name_size)
	goto fail;
	offset += name_size;
	sn->name[name_size] = '\0';
	}
	s->snapshots_size = offset - s->snapshots_offset;
	return 0;
	fail:
	qcow2_free_snapshots(bs);
	return -1;
	}

	/* add at the end of the file a new list of snapshots */
	static int qcow2_write_snapshots(BlockDriverState *bs)
	{
	BDRVQcowState *s = bs->opaque;
	QCowSnapshot *sn;
	QCowSnapshotHeader h;
	int i, name_size, id_str_size, snapshots_size;
	uint64_t data64;
	uint32_t data32;
	int64_t offset, snapshots_offset;

	/* compute the size of the snapshots */
	offset = 0;
	for(i = 0; i < s->nb_snapshots; i++) {
	sn = s->snapshots + i;
	offset = align_offset(offset, 8);
	offset += sizeof(h);
	offset += strlen(sn->id_str);
	offset += strlen(sn->name);
	}
	snapshots_size = offset;

	snapshots_offset = qcow2_alloc_clusters(bs, snapshots_size);
	bdrv_flush(bs->file);
	offset = snapshots_offset;
	if (offset < 0) {
	return offset;
	}

	for(i = 0; i < s->nb_snapshots; i++) {
	sn = s->snapshots + i;
	memset(&h, 0, sizeof(h));
	h.l1_table_offset = cpu_to_be64(sn->l1_table_offset);
	h.l1_size = cpu_to_be32(sn->l1_size);
	h.vm_state_size = cpu_to_be32(sn->vm_state_size);
	h.date_sec = cpu_to_be32(sn->date_sec);
	h.date_nsec = cpu_to_be32(sn->date_nsec);
	h.vm_clock_nsec = cpu_to_be64(sn->vm_clock_nsec);

	id_str_size = strlen(sn->id_str);
	name_size = strlen(sn->name);
	h.id_str_size = cpu_to_be16(id_str_size);
	h.name_size = cpu_to_be16(name_size);
	offset = align_offset(offset, 8);
	if (bdrv_pwrite_sync(bs->file, offset, &h, sizeof(h)) < 0)
	goto fail;
	offset += sizeof(h);
	if (bdrv_pwrite_sync(bs->file, offset, sn->id_str, id_str_size) < 0)
	goto fail;
	offset += id_str_size;
	if (bdrv_pwrite_sync(bs->file, offset, sn->name, name_size) < 0)
	goto fail;
	offset += name_size;
	}

	/* update the various header fields */
	data64 = cpu_to_be64(snapshots_offset);
	if (bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, snapshots_offset),
	&data64, sizeof(data64)) < 0)
	goto fail;
	data32 = cpu_to_be32(s->nb_snapshots);
	if (bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, nb_snapshots),
	&data32, sizeof(data32)) < 0)
	goto fail;

	/* free the old snapshot table */
	qcow2_free_clusters(bs, s->snapshots_offset, s->snapshots_size);
	s->snapshots_offset = snapshots_offset;
	s->snapshots_size = snapshots_size;
	return 0;
	fail:
	return -1;
	}

	static void find_new_snapshot_id(BlockDriverState *bs,
	char *id_str, int id_str_size)
	{
	BDRVQcowState *s = bs->opaque;
	QCowSnapshot *sn;
	int i, id, id_max = 0;

	for(i = 0; i < s->nb_snapshots; i++) {
	sn = s->snapshots + i;
	id = strtoul(sn->id_str, NULL, 10);
	if (id > id_max)
	id_max = id;
	}
	snprintf(id_str, id_str_size, "%d", id_max + 1);
	}

	static int find_snapshot_by_id(BlockDriverState bs, const char id_str)
	{
	BDRVQcowState *s = bs->opaque;
	int i;

	for(i = 0; i < s->nb_snapshots; i++) {
	if (!strcmp(s->snapshots[i].id_str, id_str))
	return i;
	}
	return -1;
	}

	static int find_snapshot_by_id_or_name(BlockDriverState bs, const char name)
	{
	BDRVQcowState *s = bs->opaque;
	int i, ret;

	ret = find_snapshot_by_id(bs, name);
	if (ret >= 0)
	return ret;
	for(i = 0; i < s->nb_snapshots; i++) {
	if (!strcmp(s->snapshots[i].name, name))
	return i;
	}
	return -1;
	}

	/* if no id is provided, a new one is constructed */
	int qcow2_snapshot_create(BlockDriverState bs, QEMUSnapshotInfo sn_info)
	{
	BDRVQcowState *s = bs->opaque;
	QCowSnapshot snapshots1, sn1, sn = &sn1;
	int i, ret;
	uint64_t *l1_table = NULL;
	int64_t l1_table_offset;

	memset(sn, 0, sizeof(*sn));

	if (sn_info->id_str[0] == '\0') {
	/* compute a new id */
	find_new_snapshot_id(bs, sn_info->id_str, sizeof(sn_info->id_str));
	}

	/* check that the ID is unique */
	if (find_snapshot_by_id(bs, sn_info->id_str) >= 0)
	return -ENOENT;

	sn->id_str = g_strdup(sn_info->id_str);
	if (!sn->id_str)
	goto fail;
	sn->name = g_strdup(sn_info->name);
	if (!sn->name)
	goto fail;
	sn->vm_state_size = sn_info->vm_state_size;
	sn->date_sec = sn_info->date_sec;
	sn->date_nsec = sn_info->date_nsec;
	sn->vm_clock_nsec = sn_info->vm_clock_nsec;

	ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1);
	if (ret < 0)
	goto fail;

	/* create the L1 table of the snapshot */
	l1_table_offset = qcow2_alloc_clusters(bs, s->l1_size * sizeof(uint64_t));
	if (l1_table_offset < 0) {
	goto fail;
	}
	bdrv_flush(bs->file);

	sn->l1_table_offset = l1_table_offset;
	sn->l1_size = s->l1_size;

	if (s->l1_size != 0) {
	l1_table = g_malloc(s->l1_size * sizeof(uint64_t));
	} else {
	l1_table = NULL;
	}

	for(i = 0; i < s->l1_size; i++) {
	l1_table[i] = cpu_to_be64(s->l1_table[i]);
	}
	if (bdrv_pwrite_sync(bs->file, sn->l1_table_offset,
	l1_table, s->l1_size * sizeof(uint64_t)) < 0)
	goto fail;
	g_free(l1_table);
	l1_table = NULL;

	snapshots1 = g_malloc((s->nb_snapshots + 1) * sizeof(QCowSnapshot));
	if (s->snapshots) {
	memcpy(snapshots1, s->snapshots, s->nb_snapshots * sizeof(QCowSnapshot));
	g_free(s->snapshots);
	}
	s->snapshots = snapshots1;
	s->snapshots[s->nb_snapshots++] = *sn;

	if (qcow2_write_snapshots(bs) < 0)
	goto fail;
	#ifdef DEBUG_ALLOC
	{
	BdrvCheckResult result = {0};
	qcow2_check_refcounts(bs, &result);
	}
	#endif
	return 0;
	fail:
	g_free(sn->name);
	g_free(l1_table);
	return -1;
	}

	/* copy the snapshot 'snapshot_name' into the current disk image */
	int qcow2_snapshot_goto(BlockDriverState bs, const char snapshot_id)
	{
	BDRVQcowState *s = bs->opaque;
	QCowSnapshot *sn;
	int i, snapshot_index;
	int cur_l1_bytes, sn_l1_bytes;

	snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
	if (snapshot_index < 0)
	return -ENOENT;
	sn = &s->snapshots[snapshot_index];

	if (qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, -1) < 0)
	goto fail;

	if (qcow2_grow_l1_table(bs, sn->l1_size, true) < 0)
	goto fail;

	cur_l1_bytes = s->l1_size * sizeof(uint64_t);
	sn_l1_bytes = sn->l1_size * sizeof(uint64_t);

	if (cur_l1_bytes > sn_l1_bytes) {
	memset(s->l1_table + sn->l1_size, 0, cur_l1_bytes - sn_l1_bytes);
	}

	/* copy the snapshot l1 table to the current l1 table */
	if (bdrv_pread(bs->file, sn->l1_table_offset,
	s->l1_table, sn_l1_bytes) < 0)
	goto fail;
	if (bdrv_pwrite_sync(bs->file, s->l1_table_offset,
	s->l1_table, cur_l1_bytes) < 0)
	goto fail;
	for(i = 0;i < s->l1_size; i++) {
	be64_to_cpus(&s->l1_table[i]);
	}

	if (qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1) < 0)
	goto fail;

	#ifdef DEBUG_ALLOC
	{
	BdrvCheckResult result = {0};
	qcow2_check_refcounts(bs, &result);
	}
	#endif
	return 0;
	fail:
	return -EIO;
	}

	int qcow2_snapshot_delete(BlockDriverState bs, const char snapshot_id)
	{
	BDRVQcowState *s = bs->opaque;
	QCowSnapshot *sn;
	int snapshot_index, ret;

	snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
	if (snapshot_index < 0)
	return -ENOENT;
	sn = &s->snapshots[snapshot_index];

	ret = qcow2_update_snapshot_refcount(bs, sn->l1_table_offset, sn->l1_size, -1);
	if (ret < 0)
	return ret;
	/* must update the copied flag on the current cluster offsets */
	ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
	if (ret < 0)
	return ret;
	qcow2_free_clusters(bs, sn->l1_table_offset, sn->l1_size * sizeof(uint64_t));

	g_free(sn->id_str);
	g_free(sn->name);
	memmove(sn, sn + 1, (s->nb_snapshots - snapshot_index - 1) * sizeof(*sn));
	s->nb_snapshots--;
	ret = qcow2_write_snapshots(bs);
	if (ret < 0) {
	/* XXX: restore snapshot if error ? */
	return ret;
	}
	#ifdef DEBUG_ALLOC
	{
	BdrvCheckResult result = {0};
	qcow2_check_refcounts(bs, &result);
	}
	#endif
	return 0;
	}

	int qcow2_snapshot_list(BlockDriverState bs, QEMUSnapshotInfo *psn_tab)
	{
	BDRVQcowState *s = bs->opaque;
	QEMUSnapshotInfo sn_tab, sn_info;
	QCowSnapshot *sn;
	int i;

	if (!s->nb_snapshots) {
	*psn_tab = NULL;
	return s->nb_snapshots;
	}

	sn_tab = g_malloc0(s->nb_snapshots * sizeof(QEMUSnapshotInfo));
	for(i = 0; i < s->nb_snapshots; i++) {
	sn_info = sn_tab + i;
	sn = s->snapshots + i;
	pstrcpy(sn_info->id_str, sizeof(sn_info->id_str),
	sn->id_str);
	pstrcpy(sn_info->name, sizeof(sn_info->name),
	sn->name);
	sn_info->vm_state_size = sn->vm_state_size;
	sn_info->date_sec = sn->date_sec;
	sn_info->date_nsec = sn->date_nsec;
	sn_info->vm_clock_nsec = sn->vm_clock_nsec;
	}
	*psn_tab = sn_tab;
	return s->nb_snapshots;
	}

	int qcow2_snapshot_load_tmp(BlockDriverState bs, const char snapshot_name)
	{
	int i, snapshot_index, l1_size2;
	BDRVQcowState *s = bs->opaque;
	QCowSnapshot *sn;

	snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_name);
	if (snapshot_index < 0) {
	return -ENOENT;
	}

	sn = &s->snapshots[snapshot_index];
	s->l1_size = sn->l1_size;
	l1_size2 = s->l1_size * sizeof(uint64_t);
	if (s->l1_table != NULL) {
	g_free(s->l1_table);
	}

	s->l1_table_offset = sn->l1_table_offset;
	s->l1_table = g_malloc0(align_offset(l1_size2, 512));

	if (bdrv_pread(bs->file, sn->l1_table_offset,
	s->l1_table, l1_size2) != l1_size2) {
	return -1;
	}

	for(i = 0;i < s->l1_size; i++) {
	be64_to_cpus(&s->l1_table[i]);
	}
	return 0;
	}