* Christian Brauner: > [Cc Florian since that ends up on libc's table sooner or later...] I'm not sure what you are after here … > On Fri, Feb 28, 2020 at 02:53:32PM +0000, David Howells wrote: >> >> I've been told that RESOLVE_* flags, which can be found in linux/openat2.h, >> should be used instead of the equivalent AT_* flags for new system calls. Is >> this the case? > > Imho, it would make sense to use RESOLVE_* flags for new system calls > and afair this was the original intention. > The alternative is that RESOLVE_* flags are special to openat2(). But > that seems strange, imho. The semantics openat2() has might be very > useful for new system calls as well which might also want to support > parts of AT_* flags (see fsinfo()). So we either end up adding new AT_* > flags mirroring the new RESOLVE_* flags or we end up adding new > RESOLVE_* flags mirroring parts of AT_* flags. And if that's a > possibility I vote for RESOLVE_* flags going forward. The have better > naming too imho. > > An argument against this could be that we might end up causing more > confusion for userspace due to yet another set of flags. But maybe this > isn't an issue as long as we restrict RESOLVE_* flags to new syscalls. > When we introduce a new syscall userspace will have to add support for > it anyway. I missed the start of the dicussion and what this is about, sorry. Regarding open flags, I think the key point for future APIs is to avoid using the set of flags for both control of the operation itself (O_NOFOLLOW/AT_SYMLINK_NOFOLLOW, O_NOCTTY) and properaties of the resulting descriptor (O_RDWR, O_SYNC). I expect that doing that would help code that has to re-create an equivalent descriptor. The operation flags are largely irrelevant to that if you can get the descriptor by other means. >> (*) It has been suggested that AT_SYMLINK_NOFOLLOW should be the default, but >> only RESOLVE_NO_SYMLINKS exists. > > I'd be very much in favor of not following symlinks being the default. > That's usually a source of a lot of security issues. But that's inconsistent with the rest of the system. And for example, if you make /etc/resolv.conf a symbolic link, a program which uses a new I/O library (with the new interfaces) will not be able to read it. AT_SYMLINK_NOFOLLOW only applies to the last pathname component anyway, so it's relatively little protection. Thanks, Florian
