Hacker News Reader

You can use the kcmp system call with KCMP_FILE argument to find out if two fds point to the same files structure (of course you must use this as the custom comparison function of a sort algorithm so you don't end up with quadratic run time).

Linux has a project called CRIU that can save and restore processes to disk without needing additional kernel modules, so pretty much all state is already gettable and settable from user space.

View on HN

I can't do that across processes, though, can I? (to see whether two processes have file descriptors pointing to the same open file) edit -- it does look like it works cross-process!

I hadn't heard of CRIU. I'll check that out. (edit: CRIU looks super useful. I think the speed/overhead of snapshotting will decide whether I can use it for this project, but I can imagine it being handy in the future regardless. Thanks for the link.)

I recommend checking out podman (or docker) - they have built-in criu support. Otherwise you’ll need some other namespacing mechanism to avoid colliding pids

Every C Playground program runs in a Docker container, so this is already perfectly set up for CRIU. I might give it a try!

Also check out kcmp man it totally allows you to compare fds across pids

Reply on news.ycombinator.com