Hello,
I am writing a user-space layer to manage SCTP sockets and provide a
high-level API for various applications to exchange data. This layer is
responsible for handling notifications (e.g. generate traces and logs),
but I would like the data messages to be handled directly by the
application. Since notifications are delivered in-band by the SCTP
stack through recvmsg(), I have something like:
---------------------------------------------------------
APP
SCTP_receive()
|
--------------------------------------|------------------
SCTP layer |
NOTIFICATION DATA
\ /
recvmsg()
user-space |
=================================|=======================
kernel |
A trivial implementation is the following:
int SCTP_receive(int sd, void *buf, size_t count)
{
do {
len = recvmsg(sd, &msg, MSG_WAITALL);
if (flags & MSG_NOTIFICATION)
handle_sctp_notification(snp);
else
return len;
} while (true);
}
Problem is that I rely on the application to call SCTP_receive() to read
any notification. In the case of a send-only application, I never read
the notifications. So I have to decouple recvmsg() from SCTP_receive()
and do the system call in my own context. Then I have to buffer all data
messages until the application calls SCTP_receive(). This overhead I
would rather not have. Ideally I would like to go read the notifications
out-of-band, but that does not seem to be possible.
---------------------------------------------------------
APP
SCTP_receive()
|
--------------------------------------|------------------
SCTP layer |
NOTIFICATION DATA
| |
recvnotif() recvmsg()
user-space | |
====================|=================|==================
kernel | |
Any suggestions?
Lionel
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