Re: [PATCH][TAKE 3] THE LINUX/I386 BOOT PROTOCOL - Breaking the 256 limit

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

H. Peter Anvin wrote:
> Alon Bar-Lev wrote:
>> diff -urNp linux-2.6.16/Documentation/i386/boot.txt 
>> linux-2.6.16.new/Documentation/i386/boot.txt
>> --- linux-2.6.16/Documentation/i386/boot.txt    2006-03-20 
>> 07:53:29.000000000 +0200
>> +++ linux-2.6.16.new/Documentation/i386/boot.txt    2006-04-14 
>> 01:55:47.000000000 +0300
>> @@ -235,11 +235,8 @@ loader to communicate with the kernel.   relevant 
>> to the boot loader itself, see "special command line options"
>>  below.
>>  
>> -The kernel command line is a null-terminated string currently up to
>> -255 characters long, plus the final null.  A string that is too long
>> -will be automatically truncated by the kernel, a boot loader may allow
>> -a longer command line to be passed to permit future kernels to extend
>> -this limit.
>> +The kernel command line is a null-terminated string. A string that is 
>> too
>> +long will be automatically truncated by the kernel.
>>  
>>  If the boot protocol version is 2.02 or later, the address of the
>>  kernel command line is given by the header field cmd_line_ptr (see
>> @@ -260,6 +257,9 @@ command line is entered using the follow
>>      covered by setup_move_size, so you may need to adjust this
>>      field.
>>  
>> +       The kernel command line *must* be 256 bytes including the
>> +       final null.
>> +
>>  
>>  **** SAMPLE BOOT CONFIGURATION
>>  
> 
> This chunk is confusing at the very best.
> 
>     -hpa
> 

Hello,

The problem is that boot loader developers did not 
understand the old statement: "A string that is too long 
will be automatically truncated by the kernel, a boot loader 
may allow a longer command line to be passed to permit 
future kernels to extend this limit."

Most of them handed the same buffer to < 2.02 protocols and 
 >= 2.0.2 protocols. When I've opened bugs against that they 
claimed that they follow instructions since the 256 limit 
was explicitly mentioned. I've ended up in patching GRUB 
my-self to allow this.

I thought that this should be made clearer... But maybe I 
did not write it too well.

I've removed the 255+1 limitation from the boot protocol 
main description, so there will be no known limit there... 
And moved it to the <2.02 section notes.

Can you please suggest a different phrasing? Or maybe you 
think that it is not needed at all... But then I have a 
problem of making boot loader fix their code.

Best Regards,
Alon Bar-Lev.