How do I get amount of queued data for UDP socket?

Question

To see how well I'm doing in processing incoming data, I'd like to measure the queue length at my TCP and UDP sockets.

I know that I can get the queue size via SO_RCVBUF socket option, and that ioctl(<sockfd>, SIOCINQ, &<some_int>) tells me the information for TCP sockets. But for UDP the SIOCINQ / FIONREAD ioctl returns only the size of next pending datagram. Is there a way how to get queue size for UDP, without having to parse system tables such as /proc/net/udp ?

Answer 1

FWIW, I did some experiments to map out the behavior of FIONREAD on different platforms.

Platforms where FIONREAD returns all the data pending in a SOCK_DGRAM socket:

Mac OS X, NetBSD, FreeBSD, Solaris, HP-UX, AIX, Windows

Platforms where FIONREAD returns only the bytes for the first pending datagram:

Linux

It might also be worth noting that some implementations include headers or other overhead bytes in the count, while others only count the payload bytes. Linux appears to return the payload size, not including IP headers.

Answer 2

As ldx mentioned, it is not supported through ioctl or getsockopt. It seems to me that the current implementation of SIOCINQ was aimed to determine how much buffer is needed to read the entire waiting buffer (but I guess it is not so useful for that, as it can change between the read of it to the actual buffer read).

There are many other telemetries which are not supported though such system calls, I guess there is no real need in normal production usage.

You can check the drops/errors through "netstat -su" , or better using SNMP (udpInErrors) if you just want to monitor the machine state.

BTW: You always have the option to hack in the Kernel code and add this value (or others).