Re: Kexec command line length

From: Vivek Goyal <vgoyal@redhat.com>
To: Neil Horman <nhorman@redhat.com>
Cc: kexec@lists.infradead.org, Neil Horman <nhorman@tuxdriver.com>
Subject: Re: Kexec command line length
Date: Tue, 15 Jan 2008 12:37:53 -0500	[thread overview]
Message-ID: <20080115173753.GB24435@redhat.com> (raw)
In-Reply-To: <20080115170950.GA24359@hmsendeavour.rdu.redhat.com>

On Tue, Jan 15, 2008 at 12:09:50PM -0500, Neil Horman wrote:
> On Tue, Jan 15, 2008 at 10:27:10AM -0500, Vivek Goyal wrote:
> > On Mon, Jan 14, 2008 at 08:43:03AM -0500, Neil Horman wrote:
> > > Hey all-
> > > 	Regarding this bug:
> > > 	http://bugzilla.kernel.org/show_bug.cgi?id=9641
> > > 	I'd like to look into putting together a patch for it, and wanted to
> > > solicit comments for the best way to go about doing it.  Currently I've got it
> > > fixed up in the Red Hat tree by bumping COMMAND_LINE_SIZE to 2048 and
> > > eliminating the reserved buffer of the x86_linux_faked_param_header, which works
> > > well, but isn't backwards compatible as Bernhard pointed out.  Given that extra
> > > constraint, I thought it woudl e best to unify the command line and reserved
> > > buffers in x86_linux_faked_param_header to one contiguour 2048 byte block and
> > > maintain a separate variable that defines the command line length based on a
> > > parsing of the UTS_VERSION.  Does that sound reasonable to everyone, or is there
> > > a better way that someone has in mind?
> > > 
> > 
> > Hi Neil,
> > 
> > Looking at UTS_VERSION and then deciding the command line length seems
> > ok. 
> > 
> > When I look at inclue/asm-x86/bootparam.h in kernel, area starting from
> > 0x2d0 to all the way up to 4K has been reserved for e820 maps and EDD buf.
> > 
> > Does that mean newer boot loaders are putting command line outside of 
> > 4K page and only putting the pointer to cmdline in 4K page. If that's the
> > case then we might have to do the same for kexec.
> > 
> 
> That would seem to be the case yes, although it appears the kernel still
> supports the old boot protocol if you want to restrict the command line length
> to the old 256 chars (see copy_boot_data)
> 

If that's the case then we probably should not be merging command_line
and reserved area. Instead we might have to put command line somewhere
else and pass the pointer to it in param page. If command line is with-in
256, then we can continue to pass it in param page. 

Thanks
Vivek

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