relayfs documentation sucks?

[bert hubert <bert.hubert@netherlabs.nl>]

Ok, I'm working furiously on my OLS presentation (Wednesday, 3pm, be
there), but I'm running into a wall with relayfs, which I intend to use to
convey large amounts of disk statistics towards userspace.

Now, I've read Documentation/filesystems/relayfs.txt many times over, and I
don't get it.

It appears there is relayfs, and 'klog' on top of that. It also appears that
to access relayed data from the kernel in userspace there is librelay.c.

On reading librelay.c, I find code sending and receiving netlink
messages, but relayfs.txt doesn't even contain the word netlink!

I then launched the 'kleak-app' sample program, but told it to look at
/relay/diskstat* instead of its own file, but it gives me unspecified
netlink errors.

Things I need to know, and which I hope to find documented somewhere:

1) Do I need to do the netlink thing?
2) What kind of messages do I need to send/receive?
3) What is the exact format userspace sees in the relayfs file? Iow, can I
   access that file w/o using librelay.c?
4) What are the semantics for reading from that file?
5) When using klog, is there only one channel?
6) does librelay.c talk to regular relayfs or to klog?

Don't get me wrong, relayfs sure looks nice for what I'm trying to do but
from userspace it is sort of a black box right now..

Thanks!
	
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