Fast interprocess messaging (2010)

lwn.net

39 points·luu··11 comments

This article is painfully old...

cross memory attach landed in 3.2 http://kernelnewbies.org/Linux_3.2#head-a5e26c6275e85a5c9c41...

kdbus is coming, but its an entirely different implementation by gkh and systemd folks, its not using AF_DBUS sockets, its bypassing the net stack and using a char device.

a more relevant article on the current kdbus is https://lwn.net/Articles/580194/

This article is from 2010 so it is well before kernel 3.2. This same author has since wrote about kdbus here: http://lwn.net/Articles/580194/

The eventual code commit has a useful description of the feature:

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.g...

Aren't there any security implications of directly accessing another process's memory?

> Either both processes must have the same ownership or the copying process must have the CAP_SYS_PTRACE capability; otherwise the copy will not be allowed.

Can someone fill me in on why IPC is important? I would have thought that most parallelism was either within a process, or across machines.

Sure. My Rails app is talking to Postgres--why should I have to go through the TCP stack for local communication? Why should my window manager have to use that to send clipboard events?

Well kdbus is arriving, but the copy to other process memory does not seem to have.

Maybe I'm misunderstanding your comment, but I think kdbus does allow you to transfer ownership of some piece of memory to another process.

Does it? I haven't seen that. It has single copy transfer, but I didnt see a memory ownership transfer/sharing.

There is a zero-copy mode, but it only makes sense for pretty large messages (>512k IIRC).

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