[U-Boot-Users] [PATCH] limit length of kernel command line in bootm

[Murray.Jensen at csiro.au]

On Thu, 30 Jun 2005 12:51:16 +0200, Wolfgang Denk writes:
>> This patch limits the length of the command line that the bootm command will
>> pass to the kernel. Note that as it stands, it uses CFG_BARGSIZE which must
>> be <= the size of the command line array used in the kernel (most boards have
>> this set to CFG_CBSIZE, which in turn is usually 256 - which is usually ok).
>> I use 1024 for both, and have a kernel patch which increases the command line
>> aray to 1024. Cheers!
>
>I don't see any improvement by this patch,  as  you  cannot  know  in
>U-Boot  which value is correct for the kernel image you are booting -

Like most other configuration variables, you have to set it correctly in
your board specific configs/*.h header file.

>ther eis no way to "ask" the kernel for this.

Obviously, since the kernel is not yet running :-)

>So your patch may cause
>booting to fail in situtations where it should work,  or  not  detect
>problems  when  they  are  there.

On the contrary, it detects a specific situation where it knows the kernel
will crash and burn without any obvious reason and refuses to boot, after
outputting a clear error message.

I was burnt by this exact thing happening, and the patch was the result,
to prevent it from ever happening again.

>In  other  words,  I don;t see any
>improvement  over  the  current  situation   which   has   the   same
>expectation: that the user knows what he is doing.

Yes, indeed - they know what they are doing, and they will ensure that the
correct number is put in their board config .h file.

>Also, a hard coded
>limit is probably a bad approach anyhow.

The size of the Linux kernel command line array is hardcoded in a number
of places in the kernel (I know, because I have a patch which increases its
size). Everyone knows this is a bad approach, and yet it has survived
unchanged in the Linux (ppc) kernel for years, up to and including v2.6 (where
there was some slight improvement when it was at least defined as a macro
in a <asm-ppc/*.h> file - previously it has been a number in numerous places
ie. unsigned char array[512]; !!!)

This patch at least catches one case where it knows the size has been
exceeded. Since the "bootargs" variable is a variable length string,
which is set by the user via the command prompt, I believe it should
be detected when that user exceeds the allowed space - the linux kernel
should not just start crashing. Cheers!
								Murray...
--
Murray Jensen, CSIRO Manufacturing & Infra. Tech.      Phone: +61 3 9662 7763
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