[syslinux] Request for Ideas

H. Peter Anvin hpa at zytor.com
Thu Aug 17 14:39:54 PDT 2006

Erwan Velu wrote:
> I've been submitting a patch t o add a com32 module able to parse the 
> DMI table.
> I'm starting now the next step : having a way to boot some different 
> menu regarding the dmi structures. I've been looking for some ideas with 
> the ethersel syntax :
> DEV [DID xxxx:yyyy[/mask]] [RID zz-zz] [SID uuuu:vvvv[/mask]] commandline
> In other hand, a nice implementation must allow to do :
> "if my bios is from this_manufacturer and the bios release = 3.4 so I 
> must start the bios update.
> I think that many configuration will request to test several parameters 
> for choosing the label to start.
> Does some of you have an idea on how to have an easy to use syntax ?
> I was thinking about something like :
> DMI [<handle>.<parameter> = <value>] and|or [<handle>.<parameter> = 
> <value>] commandline
> I think two parameters is enough else config file will become too complex.
> What does some potential futur users of this think about that ?

Actually, you can use yacc to generate a grammar which can handle 
arbitrarily complex descriptions with ease.  Since COM32 is just C, a 
yacc-generated grammar should do just fine.

Otherwise, a recursive descent parser can deal with logical expressions 
of this type easily enough.

If there are numerical values, you may need to also support numerical 
comparisons, such as > >= < <=.  In order to keep the lexer/grammar 
sane, I suggest you start from the very beginning with requiring that 
string arguments are enclosed in quotes, so that:

	foo.bar = "3"

... is a string comparison, and ...

	foo.bar = 3

... is a numeric comparison.  This is easily done by having the lexer 
produce a STRING and a NUMERIC token.

Alternatively, you can adopt the Perl convention of having "eq" "ne" etc 
for strings, and "==", "!=" etc for numbers.


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