Date: Fri, 12 Jan 2018 09:09:26 -0600 From: Kevin Day <toasty@dragondata.com> To: freebsd-hackers@freebsd.org Subject: sysctl(8) can't read IFMIB nodes Message-ID: <18D7A1E9-8564-47D7-90D7-CA2E94F7F9F7@dragondata.com>
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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(0x7fffffffda00,0x2,0x7fffffffd970,0x7fffffffd9f8,0x7fffffffe210,0=
x1b)
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?)
3) Overhauling sysctl.oidfmt and oiddescr to somehow work by names as =
well as oids so that sysctl(8) doesn't need to translate them to oids =
first
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