First of all, thanks to all who answered.
I have carefully read all of the answers and I'm trying to figure out
some points now:
1. What events?
I can't see somewhere a list of events, for which upcall function
will be invoked.
Unfortunately ADC documentation seems to be incomplete (see
http://developer.apple.com/documentation/Darwin/Reference/KPI_Reference/kpi_socket).
"Your upcall function will be called when:" is the last line in
this document.
I have downloaded xnu-1228.3.13 and I'm looking it through now.
2. Blocking vs. non-blocking?
Josh Graessley wrote:
> The only difference between blocking and non-blocking is that
blocking will block and wait if there is no space available in the
send queue
Frankly speaking it is a surprise for me, I supposed that write
function for blocking socket returns only when an operation (sending)
is actually completed.
Anyway, I suppose blocking does not work for me.
I'm writing a driver that process read / write routines from a
file system context, so I think blocking can be dangerous here.
Network Kernel Extensions Programming Guide says here:
If your code is in a performance-critical part of the kernel (as
opposed to a call from user space), you should generally perform
socket I/O asynchronously.
Moreover I think mbuf part of code must be non-blocking too
(according to this document).
3. If I get EWOULDBLOCK status from sock_sendmbuf?
What does EWOULDBLOCK status of send operation exactly means?
At the moment I suppose it means that there are no enough memory
in send buffer.
So I just should retry later, yes?
4. Blocking?
I can use blocking sockets in a separate thread anyhow.
Is using blocking sockets with an upcall function correct in general?
5. Should I get to know when a send operation actually completes?
I think a general answer is no.
When sock_sendmbuf returns I should think that the operation is done.
6. Upcall
First invoking of the upcall routine is related to sock_connect
(no matter blocking or non-blocking).
Then I should try to read at any upcall.
Am I right?
7. Mbuf
The ADC example
(see http://developer.apple.com/documentation/Darwin/Conceptual/NKEConceptual/SocketManipulation/chapter_3_section_3.html#//apple_ref/doc/uid/TP40001858-CH235-DontLinkElementID_4)
does not free mbuf in the upcall routine.
Is this a bug or a special case (related to upcall)?
Sorry for so long message,
Thank you very much for reading it.
Please correct me if I'm wrong somewhere.
Best Regards.
Igor
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