Re: [PATCH v6 00/33] block layer: split block APIs in global state and I/O

[Emanuele Giuseppe Esposito]

On 07/02/2022 19:30, Kevin Wolf wrote:
> Am 21.01.2022 um 18:05 hat Emanuele Giuseppe Esposito geschrieben:
>> Each function in the GS API will have an assertion, checking
>> that it is always running under BQL.
>> I/O functions are instead thread safe (or so should be), meaning
>> that they *can* run under BQL, but also in an iothread in another
>> AioContext. Therefore they do not provide any assertion, and
>> need to be audited manually to verify the correctness.
> 
> I wonder if we could actually do something to catch at least some kinds
> of bugs. The first conclusion from thinking about it is that we probably
> shouldn't open-code assert(qemu_in_main_thread()) everywhere, but have a
> macro or inline function for each category to be called in each function.
> 
> So an IO_CODE() macro could increase a counter in the coroutine object
> (that is decreased again at the end of the function with g_auto), and
> then GLOBAL_STATE_CODE() could not only assert that we're holding the
> BQL, but also that the counter is still 0, i.e. it is not (indirectly)
> called by an I/O function.
> 
> We may want to enable this only in debug builds, but maybe still worth a
> thought anyway?

I don't understand what is the point of the counter, do you want to use
it as a boolean flag? Would a single counter work in a multi-threaded
context? Shouldn't we have it per-thread? And why you increase it only
in coroutines?

Emanuele