[Nix-dev] Avoiding threads in the daemon

[Eelco Dolstra]

Hi,

On 18/12/14 17:32, Ludovic Courtès wrote:

> Thus, I think Nix commit 49fe95 (which introduces monitor-fd.hh, which
> uses std::thread just for convenience) should be reverted, along with
> the subsequent commits to that file; then commit 524f89 can be reverted.

I really don't want to get rid of threads because they're useful and I want to
use them more in the future (e.g. build.cc would be much simpler if it used
threads rather than the current event-driven approach; nix-daemon could handle
client connections with a thread rather than a process; etc.).

I see a few ways to get PID namespaces back:

* Do a regular fork followed by clone(... | CLONE_NEWPID | CLONE_PARENT) (after
which the intermediate process can exit).

* Call setuid/setgid via syscall() to bypass the locking in the Glibc wrappers.
However, there might be other problematic functions so this is not a great solution.

* Get the Glibc folks to provide a way to run at-fork handlers with clone().

Clearly the first option is the easiest.

-- 
Eelco Dolstra | LogicBlox, Inc. | http://nixos.org/~eelco/