【QEMU系统分析之实例篇（十九）】

2024-05-07 18:03:40

系列文章目录

第十九章 QEMU系统仿真的机器创建分析实例

文章目录

系列文章目录
- 第十九章 QEMU系统仿真的机器创建分析实例
前言
一、QEMU是什么？
二、QEMU系统仿真的机器创建分析实例
- 1.系统仿真的命令行参数
- 2.迁移对象初始化
- - migration_object_init()
  - - migration_object_check()
    - blk_mig_init()
    - ram_mig_init()
    - dirty_bitmap_mig_init()
- 3.调试输出
总结

前言

本文以 QEMU 8.2.2 为例，分析其作为系统仿真工具的工作过程，并为读者展示各种 QEMU 系统仿真的启动配置实例。
本文读者需要具备一定的 QEMU 系统仿真使用经验，并对 C 语言编程有一定了解。

一、QEMU是什么？

QEMU 是一个通用且开源的机器模拟器和虚拟机。
其官方主页是：https://www.qemu.org/

二、QEMU系统仿真的机器创建分析实例

1.系统仿真的命令行参数

QEMU 作为系统仿真工具，其入口代码在 system/main.c 文件中，初始化函数 qemu_init() 的实现在 system/vl.c 文件中。
前文完成创建目标机器的过程分析，本文将继续后续运行过程的分析，读者需要对 QEMU 系统启动过程的程序代码有所了解，相关内容可以参考《QEMU系统分析之启动篇》系列文章。

..\qemu\8.2.2-qkd\qemu-system-x86_64.exe -cpu "Penryn" -M  "q35,accel=whpx,smm=off" -m "6G" -display "sdl" -audio "sdl,model=hda" -vga "std" -L "data"

2.迁移对象初始化

这部分代码在 system/vl.c 文件中，实现如下：

int qemu_init(int argc, char **argv)
{
...
    /*
     * Note: creates a QOM object, must run only after global and
     * compat properties have been set up.
     */
    migration_object_init();
...
}

前文分析了创建后期后端驱动的过程，本文继续完成迁移对象的初始化过程。

migration_object_init()

函数 migration_object_init() 代码如下：

void migration_object_init(void)
{
    /* This can only be called once. */
    assert(!current_migration);
    current_migration = MIGRATION_OBJ(object_new(TYPE_MIGRATION));

    /*
     * Init the migrate incoming object as well no matter whether
     * we'll use it or not.
     */
    assert(!current_incoming);
    current_incoming = g_new0(MigrationIncomingState, 1);
    current_incoming->state = MIGRATION_STATUS_NONE;
    current_incoming->postcopy_remote_fds =
        g_array_new(FALSE, TRUE, sizeof(struct PostCopyFD));
    qemu_mutex_init(&current_incoming->rp_mutex);
    qemu_mutex_init(&current_incoming->postcopy_prio_thread_mutex);
    qemu_event_init(&current_incoming->main_thread_load_event, false);
    qemu_sem_init(&current_incoming->postcopy_pause_sem_dst, 0);
    qemu_sem_init(&current_incoming->postcopy_pause_sem_fault, 0);
    qemu_sem_init(&current_incoming->postcopy_pause_sem_fast_load, 0);
    qemu_sem_init(&current_incoming->postcopy_qemufile_dst_done, 0);

    qemu_mutex_init(&current_incoming->page_request_mutex);
    qemu_cond_init(&current_incoming->page_request_cond);
    current_incoming->page_requested = g_tree_new(page_request_addr_cmp);

    migration_object_check(current_migration, &error_fatal);

    blk_mig_init();
    ram_mig_init();
    dirty_bitmap_mig_init();
}

首先，调用函数 migrate_params_check()，代码如下：

migration_object_check()

代码如下：

/*
 * Check whether the parameters are valid. Error will be put into errp
 * (if provided). Return true if valid, otherwise false.
 */
bool migrate_params_check(MigrationParameters *params, Error **errp)
{
    if (params->has_compress_level &&
        (params->compress_level > 9)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "compress_level",
                   "a value between 0 and 9");
        return false;
    }

    if (params->has_compress_threads && (params->compress_threads < 1)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "compress_threads",
                   "a value between 1 and 255");
        return false;
    }

    if (params->has_decompress_threads && (params->decompress_threads < 1)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "decompress_threads",
                   "a value between 1 and 255");
        return false;
    }

    if (params->has_throttle_trigger_threshold &&
        (params->throttle_trigger_threshold < 1 ||
         params->throttle_trigger_threshold > 100)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "throttle_trigger_threshold",
                   "an integer in the range of 1 to 100");
        return false;
    }

    if (params->has_cpu_throttle_initial &&
        (params->cpu_throttle_initial < 1 ||
         params->cpu_throttle_initial > 99)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "cpu_throttle_initial",
                   "an integer in the range of 1 to 99");
        return false;
    }

    if (params->has_cpu_throttle_increment &&
        (params->cpu_throttle_increment < 1 ||
         params->cpu_throttle_increment > 99)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "cpu_throttle_increment",
                   "an integer in the range of 1 to 99");
        return false;
    }

    if (params->has_max_bandwidth && (params->max_bandwidth > SIZE_MAX)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "max_bandwidth",
                   "an integer in the range of 0 to "stringify(SIZE_MAX)
                   " bytes/second");
        return false;
    }

    if (params->has_avail_switchover_bandwidth &&
        (params->avail_switchover_bandwidth > SIZE_MAX)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "avail_switchover_bandwidth",
                   "an integer in the range of 0 to "stringify(SIZE_MAX)
                   " bytes/second");
        return false;
    }

    if (params->has_downtime_limit &&
        (params->downtime_limit > MAX_MIGRATE_DOWNTIME)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "downtime_limit",
                   "an integer in the range of 0 to "
                    stringify(MAX_MIGRATE_DOWNTIME)" ms");
        return false;
    }

    /* x_checkpoint_delay is now always positive */

    if (params->has_multifd_channels && (params->multifd_channels < 1)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "multifd_channels",
                   "a value between 1 and 255");
        return false;
    }

    if (params->has_multifd_zlib_level &&
        (params->multifd_zlib_level > 9)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "multifd_zlib_level",
                   "a value between 0 and 9");
        return false;
    }

    if (params->has_multifd_zstd_level &&
        (params->multifd_zstd_level > 20)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "multifd_zstd_level",
                   "a value between 0 and 20");
        return false;
    }

    if (params->has_xbzrle_cache_size &&
        (params->xbzrle_cache_size < qemu_target_page_size() ||
         !is_power_of_2(params->xbzrle_cache_size))) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "xbzrle_cache_size",
                   "a power of two no less than the target page size");
        return false;
    }

    if (params->has_max_cpu_throttle &&
        (params->max_cpu_throttle < params->cpu_throttle_initial ||
         params->max_cpu_throttle > 99)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "max_cpu_throttle",
                   "an integer in the range of cpu_throttle_initial to 99");
        return false;
    }

    if (params->has_announce_initial &&
        params->announce_initial > 100000) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "announce_initial",
                   "a value between 0 and 100000");
        return false;
    }
    if (params->has_announce_max &&
        params->announce_max > 100000) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "announce_max",
                   "a value between 0 and 100000");
       return false;
    }
    if (params->has_announce_rounds &&
        params->announce_rounds > 1000) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "announce_rounds",
                   "a value between 0 and 1000");
       return false;
    }
    if (params->has_announce_step &&
        (params->announce_step < 1 ||
        params->announce_step > 10000)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "announce_step",
                   "a value between 0 and 10000");
       return false;
    }

    if (params->has_block_bitmap_mapping &&
        !check_dirty_bitmap_mig_alias_map(params->block_bitmap_mapping, errp)) {
        error_prepend(errp, "Invalid mapping given for block-bitmap-mapping: ");
        return false;
    }

#ifdef CONFIG_LINUX
    if (migrate_zero_copy_send() &&
        ((params->has_multifd_compression && params->multifd_compression) ||
         (params->tls_creds && *params->tls_creds))) {
        error_setg(errp,
                   "Zero copy only available for non-compressed non-TLS multifd migration");
        return false;
    }
#endif

    if (params->has_x_vcpu_dirty_limit_period &&
        (params->x_vcpu_dirty_limit_period < 1 ||
         params->x_vcpu_dirty_limit_period > 1000)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "x-vcpu-dirty-limit-period",
                   "a value between 1 and 1000");
        return false;
    }

    if (params->has_vcpu_dirty_limit &&
        (params->vcpu_dirty_limit < 1)) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                   "vcpu_dirty_limit",
                   "is invalid, it must greater then 1 MB/s");
        return false;
    }

    return true;
}

然后，调用函数 blk_mig_init() 完成块设备的迁移初始化，代码如下：

blk_mig_init()

代码如下：

void blk_mig_init(void)
{
    QSIMPLEQ_INIT(&block_mig_state.bmds_list);
    QSIMPLEQ_INIT(&block_mig_state.blk_list);
    qemu_mutex_init(&block_mig_state.lock);

    register_savevm_live("block", 0, 1, &savevm_block_handlers,
                         &block_mig_state);
}

跟踪进入函数 register_savevm_live() ，代码如下：

/* TODO: Individual devices generally have very little idea about the rest
   of the system, so instance_id should be removed/replaced.
   Meanwhile pass -1 as instance_id if you do not already have a clearly
   distinguishing id for all instances of your device class. */
int register_savevm_live(const char *idstr,
                         uint32_t instance_id,
                         int version_id,
                         const SaveVMHandlers *ops,
                         void *opaque)
{
    SaveStateEntry *se;

    se = g_new0(SaveStateEntry, 1);
    se->version_id = version_id;
    se->section_id = savevm_state.global_section_id++;
    se->ops = ops;
    se->opaque = opaque;
    se->vmsd = NULL;
    /* if this is a live_savem then set is_ram */
    if (ops->save_setup != NULL) {
        se->is_ram = 1;
    }

    pstrcat(se->idstr, sizeof(se->idstr), idstr);

    if (instance_id == VMSTATE_INSTANCE_ID_ANY) {
        se->instance_id = calculate_new_instance_id(se->idstr);
    } else {
        se->instance_id = instance_id;
    }
    assert(!se->compat || se->instance_id == 0);
    savevm_state_handler_insert(se);
    return 0;
}

ram_mig_init()

接着对内存迁移初始化，代码如下：

void ram_mig_init(void)
{
    qemu_mutex_init(&XBZRLE.lock);
    register_savevm_live("ram", 0, 4, &savevm_ram_handlers, &ram_state);
    ram_block_notifier_add(&ram_mig_ram_notifier);
}

dirty_bitmap_mig_init()

最后，对脏位图迁移初始化，代码如下：

void dirty_bitmap_mig_init(void)
{
    QSIMPLEQ_INIT(&dbm_state.save.dbms_list);
    qemu_mutex_init(&dbm_state.load.lock);

    register_savevm_live("dirty-bitmap", 0, 1,
                         &savevm_dirty_bitmap_handlers,
                         &dbm_state);
}

3.调试输出

首先，添加跟踪调试信息，修改后的代码如下：

int qemu_init(int argc, char **argv)
{
...
    /*
     * Note: creates a QOM object, must run only after global and
     * compat properties have been set up.
     */
    huedbg_flag = 1;
    HUEDBG("\n");
    migration_object_init();
    HUEDBG("\n");
    huedbg_flag = 0;
...
}


void migration_object_init(void)
{
    HUEDBG("enter\n");
...
    HUEDBG("\n");
    migration_object_check(current_migration, &error_fatal);
    if (current_migration) {
        huedbg_dump_MigrationState(current_migration, 9);
    }
    HUEDBG("\n");
    blk_mig_init();
    HUEDBG("\n");
    ram_mig_init();
    HUEDBG("\n");
    dirty_bitmap_mig_init();
    HUEDBG("exit\n");
}

void blk_mig_init(void)
{
    QSIMPLEQ_INIT(&block_mig_state.bmds_list);
    QSIMPLEQ_INIT(&block_mig_state.blk_list);
    qemu_mutex_init(&block_mig_state.lock);

    register_savevm_live("block", 0, 1, &savevm_block_handlers,
                         &block_mig_state);
    if (block_mig_state) {
        huedbg_dump_BlkMigState(block_mig_state, 9);
    }
}


void ram_mig_init(void)
{
    qemu_mutex_init(&XBZRLE.lock);
    register_savevm_live("ram", 0, 4, &savevm_ram_handlers, &ram_state);
    ram_block_notifier_add(&ram_mig_ram_notifier);
    if (ram_state) {
        huedbg_dump_RAMState(ram_state, 9);
    }
}


void dirty_bitmap_mig_init(void)
{
    QSIMPLEQ_INIT(&dbm_state.save.dbms_list);
    qemu_mutex_init(&dbm_state.load.lock);

    register_savevm_live("dirty-bitmap", 0, 1,
                         &savevm_dirty_bitmap_handlers,
                         &dbm_state);
    huedbg_dump_DBMState(&dbm_state, 9);
}

运行后，输出信息如下：

[15556]../system/vl.c/qemu_init(3860):
[15556]../migration/migration.c/migration_object_init(178):enter
[15556]../qom/object.c/type_table_lookup(103):lookup type(migration) in hash table
[15556]../qom/object.c/object_new_with_type(789):try type_initialize(migration)
[15556]../qom/object.c/object_new_with_type(799):obj(migration) alloc
[15556]../qom/object.c/object_new_with_type(808):try object_initialize_with_type(migration)
[15556]../qom/object.c/object_initialize_with_type(568):obj with type(migration) enter
[15556]../qom/object.c/object_initialize_with_type(576):mapping obj(migration).class with type(migration).class
[15556]../qom/object.c/object_initialize_with_type(579):try object_class_property_init_all(migration)
[15556]
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