Re: [PATCH v6 02/33] include/block/block: split header into I/O and global state API

[Paolo Bonzini]

On 1/31/22 15:54, Kevin Wolf wrote:
> So I guess the decision depends on what you're going to use the
> categories in the future. I get the feeling that we have one more
> category than this series introduces:
>
> * Global State (must run from the main thread/hold the BQL)
> * I/O (can be called in any thread under the AioContext lock, doesn't
>    modify global state, drain waits for it to complete)
> * Common (doesn't even touch global state)
> * iothread dependent (can run without the BQL, but only in one specific
>    iothread while holding its AioContext lock; this would cover at least
>    AIO_WAIT_WHILE() and all of its indirect callers)

Yes, I agree.

bdrv_drained_begin and friends are somewhat like a coroutine-level 
lock/unlock primitive, so they need to be available in both the main 
thread and the iothread.  They could be called iothread dependent, 
AioContext dependent, or perhaps "global or I/O".

That said, even if they are a different category, I think it makes sense 
to leave them in the same header file as I/O functions, because I/O 
functions are locked out between drained_begin and drained_end.

Paolo