Re: sysctl question

[Paul Goyette <paul%whooppee.com@localhost>]

On Thu, 19 Jun 2008, Quentin Garnier wrote:

> On Thu, Jun 19, 2008 at 07:58:22AM -0700, Paul Goyette wrote:
> > As I indicated yesterday, I'm writing a device driver for on-DIMM memory
> > temp sensors (such as those on DDR2 FB-DIMM, some DDR2 SORDIMM, and all
> > DDR3).  The sensors have hardware limit registers for lower, upper, and
> > critical temp limits.
> >
> > sysmon_envsys(9) doesn't seem to provide a mechanism for the limits to be
> > set from userland, so I need some other way to get values into the
> > registers.  I've thought of three ways to do this:
> >
> >         1. Hardcode the limits in the driver, and don't provide any way
> >            to change them.
> >
> >         2. Modify sysmon_envsys to add a new mechanism
> >
> >         3. Add a sysctl to the driver for specifying the limits
> >
> > #1 seems rather restrictive and makes it difficult to adjust the limits
> > for testing the driver.
> >
> > #2 is a whole lot more work than I'm ready to sign up for at this time!
>
> I really thought 2 was possible through the envsysd config.  But maybe
> I'm wrong...

Christoff Egger and I had this discussion yesterday.  Basically, there 
is a mechanism for a user-specified critical-level monitoring event, but 
that's in addition to (and separate from) the "built-in" events.  And 
there's no mechanism for more than one such level, whereas the sensors 
I'm dealing with have three temp-zone boundary points and therefore four 
states:

        WARN_UNDER                  temp < low_lim
        NORMAL          low_lim  <= temp <= high_lim
        WARN_OVER       high_lim <  temp <= crit_lim
        CRIT_OVER       crit_lim <= temp

> > So that leaves #3.

Actually, there's a 4th option I just thought of:

        4. Make it a real driver and use IOCTL's

but that means burning a device major for something that you'll never 
touch after booting the system.

<snip>
> > Any suggestions on an acceptable mechanism for associating the 
> > sysctl node with the device's dev_t ?
>
> See for instance the handler in sys/net/if_tap.c.

Thanks for the pointer!


----------------------------------------------------------------------
|   Paul Goyette   | PGP DSS Key fingerprint: |  E-mail addresses:   |
| Customer Service | FA29 0E3B 35AF E8AE 6651 |  paul%whooppee.com@localhost   |
| Network Engineer | 0786 F758 55DE 53BA 7731 | pgoyette%juniper.net@localhost |
----------------------------------------------------------------------