By Neil Brown  November 9, 2017, lwn.net

• Block layer introduction part 2: the request layer
• Two new block I/O schedulers for 4.12

The Linux block layer provides an upstream interface to filesystems and block-special devices allowing them to access a multitude of storage backends in a uniform …

By Neil Brown  October 25, 2017, lwn.net

• A block layer introduction part 1: the bio layer
• [PATCH] block: replace bi_bdev with a gendisk pointer and partitions index
• [PATCH] blk: improve order of bio handling in generic_make_request()
• [PATCH] block: initial patch for on-stack per-task plugging
• [PATCH] block: provide a direct_make_request …

Linux Block IO: Introducing Multi-queue SSD Access on Multi-core Systems

Jonathan Corbet  June 5, 2013, lwn.net

• The multiqueue block layer
• Linux Block IO: Introducing Multi-queue SSD Access on Multi-core Systems
• null_blk.c

The kernel's block layer is charged with managing I/O to the system's block ("disk drive") devices. It was designed in an era when a high-performance drive …

• include/linux/dm-bufio.h
• drivers/md/dm-bufio.c

可以理解为 device-mapper framework 自己实现的简单 buf 库（dm 喜欢自己封装提供自己的 API 接口，这样的好处是可以隐藏 block layer 的一些变动，不好的地方是熟悉这些 API 需要时间，好在实现简洁易懂，实际中用到的时候可以方便查看实现细节），可以看作是 dm 的 malloc 库，dm_bufio_client 看作 buf pool 的句柄，dm_buffer 看作 pool 中单个 buf 句柄。用户有了这些句柄之后，就可以读写数据到 buf；与 malloc 不同的是，dm-bufio …

• linux/include/linux/device-mapper.h
• linux/drivers/md/dm-target.c

系统中注册的 target_type 都链入 static LIST_HEAD(_targets) 中

int dm_register_target(struct target_type *tt) 向系统中注册 target_type，如果之前已经注册过了则返回 -EEXIST，否则成功注册并返回 0

void dm_unregister_target(struct target_type *tt) 从系统中注销 target_type，如果之前没有注册过，则报错 Unregistering unrecognised target: <target_type->name> 并 BUG()，否则移出 static LIST_HEAD(_targets)

int dm_target_iterate …

• http://man7.org/linux/man-pages/man8/lsblk.8.html

• https://git.kernel.org/pub/scm/utils/util-linux/util-linux.git

• https://github.com/karelzak/util-linux

The lsblk command is part of the util-linux package. lsblk lists information about all available or the specified block devices. The lsblk command reads the sysfs …

• linux/Documentation/core-api/workqueue.rst

Whenever a driver or subsystem wants a function to be executed asynchronously it has to set up a work item pointing to that function and queue that work item on a workqueue.

There are many cases where an asynchronous process execution context is needed and …

• linux/Documentation/core-api/atomic_ops.rst

If someone wants to use xchg(), cmpxchg() and their variants, linux/atomic.h should be included rather than asm/cmpxchg.h, unless the code is in arch/* and can take care of itself.

    "compare and swap" atomically:
        1) Compares "old" with the value currently at …

• linux/Documentation/device-mapper/kcopyd.txt
• linux/drivers/md/dm-kcopyd.c

kcopyd 提供的是一个易于使用的接口，隐藏了异步：dm-kcopyd.c 重点在于 "d"，即对 kcopyd_jobs 的异步管理，而 copy 相关的具体 async IO 细节在 dm-io.c 中实现

kcopyd provides the ability to copy a range of sectors from one block-device to one or more other block-devices, with …