Re: [Qemu-devel] [PATCH v2 6/7] block/nbd-client: early fail nbd_read_reply_entry if s->quit is set

[Paolo Bonzini <pbonzini@redhat.com>]

On 19/09/2017 11:43, Vladimir Sementsov-Ogievskiy wrote:
>>
>> I'm trying to look forward to structured reads, where we will have to
>> deal with more than one server message in reply to a single client
>> request.  For read, we just piece together portions of the qiov until
>> the server has sent us all the pieces.  But for block query, I really do
>> think we'll want to defer to specialized handlers for doing further
>> reads (the amount of data to be read from the server is not known by the
>> client a priori, so it is a two-part read, one to get the length, and
>> another to read that remaining length); if we need some sort of callback
>> function rather than cramming all the logic here in the main read loop,
> 
> by patch 3 I do not mean in any way that I want to have all reading
> staff in one function, ofcourse it should be refactored
> for block-status addition. I just want to have all reading staff in one
> coroutine. Reading from ioc is sequential, so it's
> native to do it sequentially in one coroutine, without switches.

But why is that a goal?  See it as a state machine that goes between the
"waiting for header" and "waiting for payload" states.  Reading header
corresponds to read_reply_co waiting on the socket (and reading when
it's ready); reading payload corresponds to the request coroutine
waiting on the socket and reading when it's ready.

Paolo