RE: [Xen-devel] COMMAND_LINE_SIZE and MAX_CMDLINE

[Birger Tödtmann <btoedtmann@xxxxxxxxxxxxxx>]

Am Mittwoch, den 08.06.2005, 07:58 +0100 schrieb Ian Pratt:
[...]
> 
> MAX_CMDLINE is used in the definition of start_info_t, which is the structure 
> used to pass information into guests when they are created. It's part of the 
> public hypervisor interface, so you wouldn't want it dependent on the 
> particular dom0 kernel. However, it's the last item in the structure, which 
> means we could increase it without breaking backward compatibility.
> 
> I can see some justification to doing this as I've run in to trouble before 
> with iscsi root command lines. Do any of the distro kernels increase 
> COMMAND_LINE_SIZE beyond 256?

My point is that you cannot predict which guests you are going to run
and what cmd line sizes they may offer.  Currently i386 cmd line sizes
are at 256, but I don't know about Net/FreeBSD, and a 'grep
COMMAND_LINE_SIZE' on the linux kernel suggests quite a variety of
lengths up to 1024 (arm architecture).  I myself frequently increase
them to support different configuration hints for the guests, I think
that's also a reason why the size for UML currently is at 512.   So
fixing MAX_CMDLINE at 256 looks a bit .... arbitrary?  I had quite some
difficulties even to find out that *Xen* is cutting off my args, not the
kernel I am booting ;-)


Regards,
-- 
Birger Tödtmann
Technik der Rechnernetze, Institut für Experimentelle Mathematik
Universität Duisburg-Essen, Campus Essen email:btoedtmann@xxxxxxxxxxxxxx
skype:birger.toedtmann pgp:0x6FB166C9

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