sysctl(8) can't read IFMIB nodes

[John Baldwin]

On Friday, January 12, 2018 09:09:26 AM Kevin Day wrote:
> 
> IFMIB doesn't work with the command-line tool sysctl(8). src/tools/tools/ifinfo uses IFMIB correctly though, so I looked at why:
> 
> ifinfo is calling sysctlbyname() directly:
> 
>  86387 ifinfo   CALL  __sysctl(0x7fffffffe510,0x6,0x7fffffffe530,0x7fffffffe100,0,0)
>  86387 ifinfo   SCTL  "net.link.generic.ifdata.1.1"
>  86387 ifinfo   RET   __sysctl 0
> 
> But using sysctl directly doesn't:
> 
> # ktrace sysctl net.link.generic.ifdata.1.1
> sysctl: unknown oid 'net.link.generic.ifdata.1.1': No such file or directory
> 
> The problem is that sysctl(8) is calling sysctl.name2oid on it first, so that it can get type information on it:
> 
>  21090 sysctl   CALL  __sysctl(0x7fffffffda00,0x2,0x7fffffffd970,0x7fffffffd9f8,0x7fffffffe210,0x1b)
>  21090 sysctl   SCTL  "sysctl.name2oid"
>  21090 sysctl   RET   __sysctl -1 errno 2 No such file or directory
>  21090 sysctl   CALL  write(0x2,0x7fffffffd2d0,0x8)
>  21090 sysctl   GIO   fd 2 wrote 8 bytes
>        "sysctl: "
>  21090 sysctl   RET   write 8
>  21090 sysctl   CALL  write(0x2,0x7fffffffd3c0,0x29)
>  21090 sysctl   GIO   fd 2 wrote 41 bytes
>        "unknown oid 'net.link.generic.ifdata.1.1'"
> 
> This fails because in the kernel, ifmib isn't setting up oids for every possible entry under ifdata, it configures the parent node then captures every request under it.
> 
> I'm specifically looking to be able to get link state/speed on all interfaces from what's essentially a shell script using tools that only exist in a base install.
> 
> If I were trying to fix this with a patch that would likely get accepted, what's the best way of fixing this?
> 
> 1) Making IFMIB create sysctls for every interface? This would require it get involved every time an interface is added or deleted, which might not be popular because this is a very infrequently used feature.
> 
> 2) Allowing sysctl(8) to forge ahead anyway with reading/writing to sysctls without oids (maybe only if the -o flag is present?)

I would fix sysctl by extending it to handle a MIB which is written as either all
integers or with a prefix that is a name.

-- 
John Baldwin