linux-kernel - Re: [RFC 3/3] kexec: extend kexec_file

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Date:	Fri, 15 Jul 2016 14:19:51 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	AKASHI Takahiro <takahiro.akashi@...aro.org>, bhe@...hat.com,
	arnd@...db.de, linuxppc-dev@...ts.ozlabs.org,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	ebiederm@...ssion.com, bauerman@...ux.vnet.ibm.com,
	dyoung@...hat.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC 3/3] kexec: extend kexec_file_load system call

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.

Thanks,
Mark.