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

From: Alon Bar-Lev
Date: Tue Oct 11 2005 - 14:55:25 EST

Andi Kleen wrote:
Alon Bar-Lev <alon.barlev@xxxxxxxxx> writes:

+ 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.
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