On Mon, 18 Jul 2022 at 15:03, Christian Kohlschütter <christian@xxxxxxxxxxxxxxxx> wrote: > > Am 18.07.2022 um 14:21 schrieb Miklos Szeredi <miklos@xxxxxxxxxx>: > > > > On Mon, 18 Jul 2022 at 12:56, Christian Kohlschütter > > <christian@xxxxxxxxxxxxxxxx> wrote: > > > >> However, users of fuse that have no business with overlayfs suddenly see their ioctl return ENOTTY instead of ENOSYS. > > > > And returning ENOTTY is the correct behavior. See this comment in > > <asm-generic/errrno.h>: > > > > /* > > * This error code is special: arch syscall entry code will return > > * -ENOSYS if users try to call a syscall that doesn't exist. To keep > > * failures of syscalls that really do exist distinguishable from > > * failures due to attempts to use a nonexistent syscall, syscall > > * implementations should refrain from returning -ENOSYS. > > */ > > #define ENOSYS 38 /* Invalid system call number */ > > > > Thanks, > > Miklos > > That ship is sailed since ENOSYS was returned to user-space for the first time. > > It reminds me a bit of Linus' "we do not break userspace" email from 2012 [1, 2], where Linus wrote: > > Applications *do* care about error return values. There's no way in > > hell you can willy-nilly just change them. And if you do change them, > > and applications break, there is no way in hell you can then blame the > > application. Correct. The question is whether any application would break in this case. I think not, but you are free to prove otherwise. Thanks, Miklos
