Am 20.04.20 um 10:58 schrieb Miklos Szeredi: > 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. Ok, I'll try to workout with Jens, how to do optimizations... metze
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