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

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Date:	Mon, 18 Jul 2016 10:33:39 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	AKASHI Takahiro <takahiro.akashi@...aro.org>,
	ebiederm@...ssion.com, bhe@...hat.com, bauerman@...ux.vnet.ibm.com,
	arnd@...db.de, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC 3/3] kexec: extend kexec_file_load system call

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.

Thanks
Dave