block

疑惑

block jobs : Streaming, mirroring, commit,

忽然意识到，block 文件夹下，其实基本是这些 driver 的：

BlockDriver
- vmdk
- dmg
- vdi: A VDI file is a virtual disk image used by Oracle VM VirtualBox

阅读其他模块同时检测到的内容，也是比较关键的内容:

block/block-backend.c
block.c : 这也是我一直没有理解的地方，为什么将 block.c 不是放到 block 目录下，而是放到顶层目录中
block/dirty-bitmap.c
block/io.c

有趣的

BlockDriverState 和 BlockBackend 的关系是什么? ```c /*
Return the BlockDriverState attached to @blk if any, else null. */ BlockDriverState *blk_bs(BlockBackend *blk) { IO_CODE(); return blk->root ? blk->root->bs : NULL; } ```

block 代码基本分析

代码量比较大的问题，基本上都是各种后端。

block/vhdx.c
block/vvfat.c
block/ssh.c
block/rbd.c
block/qed.c
block/qcow2-refcount.c
block/qcow2-cluster.c
block/qapi.c
block/nvme.c
block/nfs.c
block/nbd.c
block/mirror.c
block/iscsi.c
block/io.c
block/file-posix.c
block/block-backend.c
block/qcow2.c : 磁盘格式

blockdev.c

前面的好几千行就是用于定义这个的
后面的就是各种 qmp 操作的

static const BlkActionOps actions[] = {
    [TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT] = {
        .instance_size = sizeof(ExternalSnapshotState),
        .prepare  = external_snapshot_prepare,
        .commit   = external_snapshot_commit,
        .abort = external_snapshot_abort,
        .clean = external_snapshot_clean,
    },
    // ... 还有很多类似的，就不拷贝了

    /* Where are transactions for MIRROR, COMMIT and STREAM?
     * Although these blockjobs use transaction callbacks like the backup job,
     * these jobs do not necessarily adhere to transaction semantics.
     * These jobs may not fully undo all of their actions on abort, nor do they
     * necessarily work in transactions with more than one job in them.
     */
};

在 qmp_transaction 中的，根据命令来调用这些内容:

block.c

几乎所有的函数都是 bdrv 开头的
- 应该就是 BlockDriverState 的缩写了

一些 backtrace

`io_uring`

typedef enum BlockdevAioOptions {
    BLOCKDEV_AIO_OPTIONS_THREADS,
    BLOCKDEV_AIO_OPTIONS_NATIVE,
#if defined(CONFIG_LINUX_IO_URING)
    BLOCKDEV_AIO_OPTIONS_IO_URING,
#endif /* defined(CONFIG_LINUX_IO_URING) */
    BLOCKDEV_AIO_OPTIONS__MAX,
} BlockdevAioOptions;

其中 native 模式指的是？preadv 和 pwritev 吗？
main
- qemu_main
  - qemu_main_loop
    - main_loop_wait
      - os_host_main_loop_wait
        
        glib_pollfds_poll
        
        g_main_context_dispatch
        
        aio_ctx_dispatch
        
        aio_dispatch
        
        aio_dispatch_handlers
        
        aio_dispatch_handler
        
        virtio_queue_notify_vq
        
        virtio_blk_handle_vq
        
        virtio_blk_submit_multireq
        
        submit_requests
        
        blk_aio_preadv
        
        blk_aio_prwv
        
        aio_co_enter
        
        qemu_aio_coroutine_enter
        
        qemu_coroutine_switch
        
        ??
        
        __correctly_grouped_prefixwc
        
        coroutine_trampoline
        
        blk_aio_read_entry
        
        blk_co_do_preadv_part
        
        bdrv_co_preadv_part
        
        bdrv_aligned_preadv
        
        qcow2_co_preadv_part
        
        qcow2_get_host_offset
        
        qcow2_cache_do_get
        
        bdrv_pread
        
        bdrv_co_pread
        
        bdrv_co_preadv
        
        bdrv_co_preadv_part
        
        bdrv_aligned_preadv
        
        bdrv_driver_preadv
        
        luring_co_submit
        
        luring_do_submit
跟踪一下，这是两层的 block driver 的，首先是 qcow2，然后是 file 的

block job

block_job_add_bdrv 的调用者
- block/commit.c
- block/mirror.c
- block/stream.c

block dirty bitmap

qmp ：没办法，不搞的话，dirty bitmap 是没有办法维持生活的

grep 一下目前对于 qmp 的所有问题，尝试将 qmp 和 qemu option 融合一下
https://gist.github.com/rgl/dc38c6875a53469fdebb2e9c0a220c6c
https://wiki.qemu.org/Documentation/QMP

看看 coroutine_fn 的实现和效果

static coroutine_fn int ssh_read(BDRVSSHState *s, BlockDriverState *bs,
                                 int64_t offset, size_t size,
                                 QEMUIOVector *qiov)

nfs 也可以直接做后端，不理解啊

block/nvme.c 是通过 iommu 的，

其他的奇怪后端

quorum

继续看看的

BlockDriver 似乎有很多抽象的后端，也就是后端里面还有后端了。

static BlockDriver bdrv_dmg = {
    .format_name    = "dmg",

[ ] 什么是 filter

bdrv_drop_filter

关于 scsi 的代码

scsi/ block/iscsi.c block/iscsi-opts.c

这下面有一个 scsi/qemu-pr-helper.c 做什么的?

使用 alpine.sh 中的配置之后:

如果是发起 io :

coroutine_trampoline
- blk_aio_write_entry
  - blk_co_do_pwritev_part
    - bdrv_co_pwritev_part
      - bdrv_aligned_pwritev
        
        bdrv_driver_pwritev
        
        raw_co_pwritev
        
        bdrv_co_pwritev
        
        bdrv_co_pwritev_part
        
        bdrv_aligned_pwritev
        
        bdrv_driver_pwritev
        
        iscsi_co_writev

如果是从 target (server) 哪里接受到消息，整个流程都是很熟悉了:

os_host_main_loop_wait
- glib_pollfds_poll
  - g_main_context_dispatch
    - g_main_context_dispatch_unlocked
      - aio_ctx_dispatch
        
        aio_dispatch
        
        aio_dispatch_handlers
        
        aio_dispatch_handler
        
        iscsi_process_read

iscsi_process_read(void *arg)
{
    IscsiLun *iscsilun = arg;
    struct iscsi_context *iscsi = iscsilun->iscsi;

    qemu_mutex_lock(&iscsilun->mutex);
    iscsi_service(iscsi, POLLIN);
    iscsi_set_events(iscsilun);
    qemu_mutex_unlock(&iscsilun->mutex);
}

这里的 iscsi_service 就是调用的 libiscsi 的服务了:

/nix/store/ykvbkghvny9hfmxfzl0mlrjwxxzg34y2-libiscsi-1.20.0/include/iscsi/iscsi.h

看上去复杂的逻辑，例如 openiscs 都是在 openiscsi 中了:

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