Re: ifconfig tun(N) destroy does not work !

On Mon, 5 Sep 2005, Stay d wrote:

> maybe I haven´t read something what I souhld read it, and if it is true 
> I am sorry for anoying you.
>
> Let me ask you for tun devices.
>
> roztyly# ifconfig tun1 destroy
> ifconfig: SIOCIFDESTROY: Invalid argument
>
> I found out from manual page tun(4) that:
>
> "These network interfaces persist until the if_tun.ko module is unloaded 
> (if tun is built into your kernel, the network interfaces cannot be 
> removed)."
>
> Of course the generic kernel defines "device tun", so I commented the 
> line and recompiled the kernel.
>
> After that, I tried again "destroy command" and with no changes.
>
> I tried "create command" and the same error message happens.

Your observation is correct: unlike most clonable network device drivers, 
tun and tap interface cloning is driven by devfs events, and not by 
network interface clone events controlled using ifconfig create/destroy.

I was actually bumping into this yesterday since I wanted to force the 
garbage collection of a tap device in order to try to trigger a kernel bug 
involving interface removal, and there is currently no explicit way to do 
this.  devfs will reclaim the tap device node, if unused, when vnode 
pressure requires that new vnodes become available.  I.e., when memory use 
starts to go up, the unused tun and tap nodes will be recycled as needed. 
Until that time, the device node and network interface will hang around in 
case needed.  A tun/tap node and interface will be created as a result of 
a lookup in /dev.  I.e., stat /dev/tun10.

In a number of ways, I prefer the explicit cloning behavior to implicit -- 
i.e., might prefer it if explicit "ifconfig create tap0" caused the device 
node to appear.  On the other hand, one nice advantage to the devfs 
cloning model is that you can make a /dev/tun automatically return the 
first unused node, rather than requiring a sweep through node numbers and 
explicit allocation and management of interface numbers, which is very 
nice from the perspective of automated configuration.

Robert N M Watson

>
> roztyly# kldstat
> Id Refs Address    Size     Name
> 1    9 0xc0400000 5bb9fc   kernel
> 2   16 0xc09bc000 63f04    acpi.ko
> 3    1 0xc1848000 23000    nfsserver.ko
> 4    1 0xc18b0000 1a000    linux.ko
> 6    1 0xc2926000 5000     if_gif.ko
>
> roztyly# ifconfig tun10 create
> ifconfig: SIOCIFCREATE: Invalid argument
>
> roztyly# kldstat
> Id Refs Address    Size     Name
> 1   10 0xc0400000 5bb9fc   kernel
> 2   16 0xc09bc000 63f04    acpi.ko
> 3    1 0xc1848000 23000    nfsserver.ko
> 4    1 0xc18b0000 1a000    linux.ko
> 6    1 0xc2926000 5000     if_gif.ko
> 7    1 0xc2910000 5000     if_tun.ko
>
> It seems automatic loading if_tun.ko and if_gif.ko works well.
>
> Opposite to tun device is gif device which works fine:
>
> roztyly# kldstat
> Id Refs Address    Size     Name
> 1   10 0xc0400000 5bb9fc   kernel
> 2   16 0xc09bc000 63f04    acpi.ko
> 3    1 0xc1848000 23000    nfsserver.ko
> 4    1 0xc18b0000 1a000    linux.ko
> 6    1 0xc2926000 5000     if_gif.ko
> 7    1 0xc2910000 5000     if_tun.ko
>
> roztyly# kldunload -v -i 6
> Unloading if_gif.ko, id=6
>
> roztyly# kldunload -v -i 7
> Unloading if_tun.ko, id=7
>
> roztyly# kldstat
> Id Refs Address    Size     Name
> 1    8 0xc0400000 5bb9fc   kernel
> 2   16 0xc09bc000 63f04    acpi.ko
> 3    1 0xc1848000 23000    nfsserver.ko
> 4    1 0xc18b0000 1a000    linux.ko
>
> roztyly# ifconfig gif0 create
>
> roztyly# ifconfig gif0
> gif0: flags=8010<POINTOPOINT,MULTICAST> mtu 1280
>
> roztyly# ifconfig gif0 destroy
>
> roztyly# ifconfig gif0
> ifconfig: interface gif0 does not exist
>
> roztyly# kldstat
> Id Refs Address    Size     Name
> 1    9 0xc0400000 5bb9fc   kernel
> 2   16 0xc09bc000 63f04    acpi.ko
> 3    1 0xc1848000 23000    nfsserver.ko
> 4    1 0xc18b0000 1a000    linux.ko
> 7    1 0xc2910000 5000     if_gif.ko
>
> roztyly# ifconfig tun0 create
> ifconfig: SIOCIFCREATE: Invalid argument
>
> roztyly# kldstat
> Id Refs Address    Size     Name
> 1   10 0xc0400000 5bb9fc   kernel
> 2   16 0xc09bc000 63f04    acpi.ko
> 3    1 0xc1848000 23000    nfsserver.ko
> 4    1 0xc18b0000 1a000    linux.ko
> 7    1 0xc2910000 5000     if_gif.ko
> 8    1 0xc2926000 5000     if_tun.ko
>
> roztyly# ifconfig tun0 destroy
> ifconfig: interface tun0 does not exist
>
> roztyly# kldstat
> Id Refs Address    Size     Name
> 1   10 0xc0400000 5bb9fc   kernel
> 2   16 0xc09bc000 63f04    acpi.ko
> 3    1 0xc1848000 23000    nfsserver.ko
> 4    1 0xc18b0000 1a000    linux.ko
> 7    1 0xc2910000 5000     if_gif.ko
> 8    1 0xc2926000 5000     if_tun.ko
>
> roztyly#
>
> I use tspc2 (freenet6) port, and of course the starting/stopping scripts
> deos not work as you and me expect. :(
>
> Dan
>
> Bye
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