On Sat, Apr 18, 2020 at 10:23 PM Stefan Metzmacher <metze@xxxxxxxxx> wrote: > > Am 18.04.20 um 21:00 schrieb Miklos Szeredi: > > On Sat, Apr 18, 2020 at 8:36 PM Stefan Metzmacher <metze@xxxxxxxxx> wrote: > >> > >> Hi Miklos, > >> > >>> POSIX defines faccessat() as having a fourth "flags" argument, while the > >>> linux syscall doesn't have it. Glibc tries to emulate AT_EACCESS and > >>> AT_SYMLINK_NOFOLLOW, but AT_EACCESS emulation is broken. > >>> > >>> Add a new faccessat(2) syscall with the added flags argument and implement > >>> both flags. > >>> > >>> The value of AT_EACCESS is defined in glibc headers to be the same as > >>> AT_REMOVEDIR. Use this value for the kernel interface as well, together > >>> with the explanatory comment. > >> > >> It would be nice if resolv_flags would also be passed in addition to the > >> at flags. > >> See:https://lore.kernel.org/linux-api/CAHk-=wiaL6zznNtCHKg6+MJuCqDxO=yVfms3qR9A0czjKuSSiA@xxxxxxxxxxxxxx/ > >> > >> We should avoid expecting yet another syscall in near future. > > > > What is the objection against > > > > openat(... O_PATH) > > foobarat(fd, AT_EMPTY_PATH, ...) > > openat2(), foobarat(), close() are 3 syscalls vs. just one. That's not a good argument. We could have a million specialized syscalls that all do very useful things. Except it would be a nightmare in terms of maintenance... "do one thing and do it well" > As we have the new features available, I think it would be > good to expose them to userspace for all new syscalls, so > that applications can avoid boiler plate stuff around each syscall > and get better performance in a world where context switches are not for > free. The io-uring guys are working on that problem, AFAIK. Thanks, Miklos
