On Wed, Aug 19, 2020 at 09:43:40AM +0200, peterz@xxxxxxxxxxxxx wrote: > On Tue, Aug 18, 2020 at 06:44:47PM +0100, Matthew Wilcox wrote: > > On Tue, Aug 18, 2020 at 07:34:00PM +0200, Christian Brauner wrote: > > > The only remaining function callable outside of kernel/fork.c is > > > _do_fork(). It doesn't really follow the naming of kernel-internal > > > syscall helpers as Christoph righly pointed out. Switch all callers and > > > references to kernel_clone() and remove _do_fork() once and for all. > > > > My only concern is around return type. long, int, pid_t ... can we > > choose one and stick to it? pid_t is probably the right return type > > within the kernel, despite the return type of clone3(). It'll save us > > some work if we ever go through the hassle of growing pid_t beyond 31-bit. > > We have at least the futex ABI restricting PID space to 30 bits. Ok, looking into kernel/futex.c I see pid_t pid = uval & FUTEX_TID_MASK; which is probably what this referes to and /proc/sys/kernel/threads-max is restricted to FUTEX_TID_MASK. Afaict, that doesn't block switching kernel_clone() to return pid_t. It can't create anything > FUTEX_TID_MASK anyway without yelling EAGAIN at userspace. But it means that _if_ we were to change the size of pid_t we'd likely need a new futex API. Christian
