sysctl filesystem ?

[Arnaud Lacombe]

On Mon, Jun 25, 2012 at 8:13 PM, Garrett Cooper <yanegomi at gmail.com> wrote:
> On Mon, Jun 25, 2012 at 5:03 PM, Arnaud Lacombe <lacombar at gmail.com> wrote:
>> Hi folks,
>>
>> I find myself in a situation where I need to directly explore the
>> sysctl(8) tree from my program. The tricky part is this:
>>
>> from `src/sbin/sysctl.c':
>> /*
>>  * These functions uses a presently undocumented interface to the kernel
>>  * to walk the tree and get the type so it can print the value.
>>  * This interface is under work and consideration, and should probably
>>  * be killed with a big axe by the first person who can find the time.
>>  * (be aware though, that the proper interface isn't as obvious as it
>>  * may seem, there are various conflicting requirements.
>>  */
>>
>> AFAIT, the whole interface used by sysctl(8) to explore the sysctl
>> tree (ie. list, name, get description) is undocumented. This comment
>> has been there for about, well... 17 years. No matter to say that it
>> is highly unlikely anyone is ever gonna design that perfect interface.
>> Right now, I am left with no choice but to figure out how that stuff
>> work, which I foresee will be a real PITA. No choice ? Well, not so
>> much. About 12 years ago a filesystem interface was written for
>> sysctl, namely scfs(4). It was authored by Kelly Yancey and (?) Boris
>> Popov. Unfortunately, time passed and no code is any longer publicly
>> available. URLs are either no longer valid or password-protected.
>>
>> This interface would just be perfect for my use-case. No need to spend
>> time decoding a prehistoric interface, no need to craft custom
>> accessors. I would just have to use standard POSIX file interface...
>> if the code was available.
>>
>> I was hoping some of the people on this list would either, have the
>> scfs(4) code on their drives/tapes, or have a way to contact the
>> original author(s) and thus have a chance to get that code ?
>>
>> Thanks in advance,
>>  - Arnaud
>>
>> ps: I know the code will certainly have to be fixed, but that is still
>> the best option I've got so far.
>
> Alternatively, the interface could just be documented (from
> sys/kern/kern_sysctl.c):
>
> /*
>  * "Staff-functions"
>  *
>  * These functions implement a presently undocumented interface
>  * used by the sysctl program to walk the tree, and get the type
>  * so it can print the value.
>  * This interface is under work and consideration, and should probably
>  * be killed with a big axe by the first person who can find the time.
>  * (be aware though, that the proper interface isn't as obvious as it
>  * may seem, there are various conflicting requirements.
>  *
>  * {0,0}        printf the entire MIB-tree.
>  * {0,1,...}    return the name of the "..." OID.
>  * {0,2,...}    return the next OID.
>  * {0,3}        return the OID of the name in "new"
>  * {0,4,...}    return the kind & format info for the "..." OID.
>  * {0,5,...}    return the description the "..." OID.
>  */
>
> I know 2 closed-source versions that have wholesale stolen/"borrowed"
> the code from sysctl(3), and I adapted the sysctl(8) code for my own
> uses for the cython derivative I made here [1].
>
I guess I will have no choice but to write a third...

- Arnaud

> Thanks,
> -Garrett
>
> 1. http://sourceforge.net/projects/sysctl/