From: Christian Brauner > Sent: 28 June 2022 14:13 > > On Sun, Jun 19, 2022 at 11:42:28AM +0100, Ralph Corderoy wrote: > > Hi Matthew, thanks for replying. > > > > > > The need for O_CLOFORK might be made more clear by looking at a > > > > long-standing Go issue, i.e. unrelated to system(3), which was started > > > > in 2017 by Russ Cox when he summed up the current race-condition > > > > behaviour of trying to execve(2) a newly created file: > > > > https://github.com/golang/go/issues/22315. > > > > > > The problem is that people advocating for O_CLOFORK understand its > > > value, but not its cost. Other google employees have a system which > > > has literally millions of file descriptors in a single process. > > > Having to maintain this extra state per-fd is a cost they don't want > > > to pay (and have been quite vocal about earlier in this thread). > > > > So do you agree the userspace issue is best solved by *_CLOFORK and the > > problem is how to implement *_CLOFORK at an acceptable cost? > > > > OTOH David Laight was making suggestions on moving the load to the > > fork/exec path earlier in the thread, but OTOH Al Viro mentioned a > > ‘portable solution’, though that could have been to a specific issue > > rather than the more general case. > > > > How would you recommend approaching an acceptable cost is progressed? > > Iterate on patch versions? Open a bugzilla.kernel.org for central > > tracking and linking from the other projects? ..? > > Quoting from that go thread > > "If the OS had a "close all fds above x", we could use that. (I don't know of any that do, but it sure > would help.)" > > So why can't this be solved with: > close_range(fd_first, fd_last, CLOSE_RANGE_CLOEXEC | CLOSE_RANGE_UNSHARE)? > e.g. > close_range(100, ~0U, CLOSE_RANGE_CLOEXEC | CLOSE_RANGE_UNSHARE)? That is a relatively recent linux system call. Although it can be (mostly) emulated by reading /proc/fd - but that may not be mounted. In any case another thread can open an fd between the close_range() and fork() calls. (I can't remember what I said before :-) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
