On Mon, Jul 18, 2016 at 10:30:24AM +0800, Dave Young wrote: > On 07/15/16 at 02:19pm, Mark Rutland wrote: > > On Fri, Jul 15, 2016 at 09:09:55AM -0400, Vivek Goyal wrote: > > > On Tue, Jul 12, 2016 at 10:42:01AM +0900, AKASHI Takahiro wrote: > > > > > > [..] > > > > -SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd, > > > > +SYSCALL_DEFINE6(kexec_file_load, int, kernel_fd, int, initrd_fd, > > > > unsigned long, cmdline_len, const char __user *, cmdline_ptr, > > > > - unsigned long, flags) > > > > + unsigned long, flags, const struct kexec_fdset __user *, ufdset) > > > > > > Can one add more parameters to existing syscall. Can it break existing > > > programs with new kernel? I was of the impression that one can't do that. > > > But may be I am missing something. > > > > I think the idea was that we would only look at the new params if a new > > flags was set, and otherwise it would behave as the old syscall. > > > > Regardless, I think it makes far more sense to add a kexec_file_load2 > > syscall if we're going to modify the prototype at all. It's a rather > > different proposition to the existing syscall, and needs to be treated > > as such. > > I do not think it is worth to add another syscall for extra fds. > We have open(2) as an example for different numbers of arguments > already. Did we change the syscall interface for that? I was under the impression that there was always one underlying syscall, and the C library did the right thing to pass the expected information to the underlying syscall. That's rather different to changing the underlying syscall. Regardless of how this is wrapped in userspace, I do not think modifying the existing prototype is a good idea, and I think this kind of extension needs to be a new syscall. Thanks, Mark.
