sysctl(3) man page examples

[Patrick Kelsey]

On Sun, Jun 28, 2015 at 2:26 AM, Patrick Kelsey <pkelsey at freebsd.org> wrote:

>
>
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> On Sat, Jun 27, 2015 at 6:02 PM, Sean Bruno <sbruno at ignoranthack.me>
> wrote:
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>> sysctl(3) specifies three easy to understand examples.
>>
>> The first appears to depend on a FreeBSD libc() function or library that
>> is missing, "printkproc()".  Is this a deprecated/deleted function from
>> the past?
>>
>
> This example was committed in r71409, which was between the 4.2 and 4.3
> releases.  Today, and at that time, the result of fetching a particular
> kern.proc.pid is a struct kinfo_proc, not struct kinfo_kproc (which did and
> does not exist).  There appears to never have been a printkproc() function
> (nor print_kproc(), nor printproc(), nor print_proc()) - this seems to be a
> function that is assumed to exist elsewhere in the unseen parts of the
> example program.
>
>
>>
>> The second example works just fine.
>>
>> The third accesss user.cs_path which seems to be empty across all
>> platforms.  I'm not sure if we should replace this example with
>> something more meaningful(that is to say that its proper for
>> user.cs_path to be empty) or if there is a bug causing user.cs_path to
>> be empty.
>>
>>
> This appears to be a bug that was introduced almost three years ago in
> r240176. sysctl() in lib/libc/gen/sysctl.c has special handling for
> USER_CS_PATH that returns the value of _PATH_STDPATH, which is
> "/usr/bin:/bin:/usr/sbin:/sbin".  However, this special handling for
> USER_CS_PATH was short circuited by r240176, which introduced the
> requirement that __sysctl() return ENOENT in order to reach the special
> USER_CS_PATH handling.  However, __sysctl() doesn't return ENOENT for
> USER_CS_PATH because there is a sysctl entry for it (containing an empty
> string) that is created in sys/kern/kern_mib.c, apparently so that
> user.cs_path exists when enumerating the names in the sysctl tree.
>

A patch for this is posted for review at https://reviews.freebsd.org/D2945.

-Patrick