Re: [PATCH 1/1] 2.6.14-rc3 x86: COMMAND_LINE_SIZE

[Alon Bar-Lev <alon.barlev@gmail.com>]

Andi Kleen wrote:
> Alon Bar-Lev <alon.barlev@gmail.com> writes:
> 
>>+config COMMAND_LINE_MAX_SIZE
>>+	int "Maximum kernel command-line size"
>>+	default 512
>>+	help
>>+	  This option allows you to specify maximum kernel command-line
>>+	  for kernel to handle.
> 
> 
> I think making that a config is a really bad idea. What happens
> when the user specifies a very large value. Or a very small one?
> There are subtle dependencies with the boot loader, so this is
> mostly a lie anyways.  And it doesn't really safe enough memory to 
> bother with a CONFIG.

I don't understand this dependency. The cmd_line_ptr is a 
null terminated string which set by the boot loader.
The kernel reads this string until the null or 
COMMAND_LINE_MAX_SIZE.
If the user specified too large buffer or too small buffer 
it won't reflect the boot loader since it sets the maximum 
sizeof the buffer, and the kernel truncates it.

> Also the last time I tried to increase this all kind of systems
> with old bootloaders exploded (e.g. lilo on systems with large EDID
> information - search the archives). Have these issues been resolved now? 
> If yes then I would suggest to just double the default.
> If not it cannot be changed anyways.

I've looked at the sources of lilo and grub, both truncate 
the command line to 256 into the old protocol and set the 
cmd_line_ptr to point to the same place.

This change will no affect current implementation of the 
bootloader, but will allow them to change the code to set 
the cmd_line_ptr to the full command line.

I think that the maximum size should be set to 1024, but 
since the kernel allocates a static buffer, users may wish 
to optimize it. So I think that a configuration option is 
the right place.

Best Regards,
Alon Bar-Lev.