On Thu, May 23, 2019 at 02:34:31PM -0700, Linus Torvalds wrote: > On Thu, May 23, 2019 at 11:22 AM Alexey Dobriyan <adobriyan@xxxxxxxxx> wrote: > > > > > This is v2 of this patchset. > > > > We've sent fdmap(2) back in the day: > > Well, if the main point of the exercise is performance, then fdmap() > is clearly inferior. > > Sadly, with all the HW security mitigation, system calls are no longer cheap. > > Would there ever be any other reason to traverse unknown open files > than to close them? I have had lively discussions and interestingly worded mails on account of all of this. But noone has brought up this scenario. Florian also said that it's not needed [1]. If we really want something like that we don't really need a new syscall I think. We can just do a prctl() command or fcntl() command that will give you back the next open fd. There's imho crazy ideas out there what people expect a multi-close file descriptor solution to look like. Service manager people apparently think it would be a great idea to have a syscall that takes an array of fds which the kernel is supposed to leave open and close all others, basically "close all of the fds only leave out those I tell you". I think for such a use-cases they can push for a prctl(PR_GET_NEXTFD, 2) or a fcntl(2, F_GET_NEXTFD) and implement that in userspace. I really only care about having a performant solution to closing a range of fds that's a little more flexible than closefrom() without going all crazy generic and copying (possibly) large bits of data between kernel- and userspace. close_range() is really something I've picked up on the side because the current state has bothered me (and others) a long time whenever I have to have my userspace hat on. With Al being in favor of it this seemed like we should do it. I actually wanted to have Jann's and my clone6() version on the table by now since that would unblock larger things like the time namespace patchset. In any case I'll send v3 with my max()/min() braino fixed that Oleg thankfully spotted and the split into two patches that Arnd suggested. [1]: https://lkml.org/lkml/2019/5/21/516
