Re: [RFC 3/3] kexec: extend kexec_file_load system call

From: Dave Young
Date: Sun Jul 17 2016 - 22:33:54 EST

On 07/15/16 at 09:09am, 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.

It will not break existing programs because we can use the new param only
when the new flag is set.

But we have a case below, but I think it is fine?
Originally kexec_file_load with the new flags will fail, but now it will
succeed and will access the new argument.