dm-bufio
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 …
more ...struct target_type
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 …
lsblk - list information about block devices
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 …
Concurrency Managed Workqueue (cmwq)
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 …
more ...atomic_xchg & atomic_cmpxchg
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 …kcopyd
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 …
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