Re: do we have a generic string-number sysctl mapping library ?

On Fri, Jun 27, 2014 at 11:27:56AM +0200, Trond Endrest?l wrote:
> On Fri, 27 Jun 2014 11:14+0200, Luigi Rizzo wrote:
> 
> > Hi,
> > I have frequently found myself using sysctls to control some kernel
> > feature where a string would be a better (and sometimes the only)
> > option than using a numeric value, yet the internal representation
> > should be numeric for speed and robustness.
> > Examples are the kern.timecounter, the default scheduler in dummynet,
> > and now in netmap the selection between native and emulated mode.
> > I am sure many of you can come up with other cases.
> > 
> > I wonder if we have some support for that already in the sysctl code,
> > or i should build a generic one next time i need to do that.
> 
> In C, according to sysctl(3) you could use sysctlnametomib().
> I might have misinterpreted the problem domain.

different problem. Example below:
right now i have dev.netmap.admode which can assume integer values,
i do not need a special handler, and the code in the kernel uses
1, 2 or "everything else" to decide what to do (resetting
"everything else" to 0 opportunistically).

I want to have a generic handler that accepts a set of predefined
string values (specifically "any native emulated") and converts
them to integers through some user-specificed mapping so the
kernel can still do the quick tests but users don't have
to remember what '2' means

cheers
luigi