The return value of tgt_ops->handle_io_async is never checked

[mattysweeps]

lib/ublksrv.c invokes q->tgt_ops->handle_io_async(local_to_tq(q), &io->data); but never checks the return value of handle_io_async. Looking at the code, this is the only place where handle_io_async is invoked.

The function returns an int, which could be used as a signal that target failed to submit the IO asynchronously. I'm not sure what the library should do in this case, but I think the library should do something.

[ming1]

Good catch.

I think it should be fine/enough to define its return value as 'void', and the similar one could be submit_bio() in linux kernel. The benefit is one simpler
interface. Then we can just add one warn or assert() in case of non-zero return
value of ->handle_io_async()?

What do you think of this way?

Another way is to fail the current command in case of non-zero return value,
but looks it is not flexible as the above style.

[mattysweeps]

I think returning void is acceptable and the option I prefer.

At first I thought the return code could be used by libublksrv to automatically call ->ublksrv_complete_io with an error result, but why not make this the responsibility of ->handle_io_async? (which is the case today). Besides, a buggy ->handle_io_async implementation could still return 0 when it shouldn't and drop an IO request. Better to document the contract that the target MUST call ->ublksrv_complete_io, even if an error occurs, for each invocation of ->handle_io_async.