RE: [Xen-devel] COMMAND_LINE_SIZE and MAX_CMDLINE

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> whereas COMMAND_LINE_SIZE is used inside the Linux kernel and 
> can be adjusted there (it already has different values for 
> different plat- forms), Xen uses another constant, 
> MAX_CMDLINE, at different places where start preparations are 
> done.  Unfortunately, MAX_CMDLINE is set to a fixed 256 in 
> xen/include/public/xen.h without consulting which value is 
> possible for dom0 kernels (linux/include/asm-xen/asm-i386/setup.h)
> which can then lead to a cmd line cut-off.   Is there special 
> reason why
> this is the case?  

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?

Ian 

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