sysctl question

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

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!

So that leaves #3.

Adding the sysctl itself is relatively straightforward.  But there's a 
catch!

I need to use a sysctl helper function to validate the user-specified 
value, and then stuff it into the device's registers.  The helper itself 
is once again relatively straightforward, except that it needs to find 
the dev_t->softc in order to update the hardware.

Any suggestions on an acceptable mechanism for associating the sysctl 
node with the device's dev_t ?

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