kern/186449: ifconfig(8) fails to autoload if_tap.ko when creating vmnet interface

[Valentin Davydov]

>Number:         186449
>Category:       kern
>Synopsis:       ifconfig(8) fails to autoload if_tap.ko when creating vmnet interface
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Feb 04 12:10:00 UTC 2014
>Closed-Date:
>Last-Modified:
>Originator:     Valentin Davydov
>Release:        10.0-STABLE
>Organization:
State Optical Institute
>Environment:
FreeBSD pv.local 10.0-STABLE FreeBSD 10.0-STABLE #6 r261230: Tue Jan 28 22:12:46 MSK 2014     val at pv.local:/usr/obj/usr/src/sys/GENERIC  amd64
>Description:
ifconfig(8) utility has an ability to automatically load necessary kernel module when creating first instance of a new (say, dynamic) interface. Sometimes it works (e.g. ifconfig crate tap0) and sometimes doesn't (ifconfig create vmnet0).
>How-To-Repeat:
Boot with a clean GENERIC kernel. Become root. Say "ifconfig vmnet0 create". You should get "ifconfig: SIOCIFCREATE2: Invalid argument" diagnostics. At the same time "ifconfig tap0 create" works as expected (as well as "ifconfig vmnetN create" afterwards, when if_tap.ko is already loaded).
>Fix:
This problem is most probably caused by the ifmaybeload() function. It implicitly derives kernel module name from the interface name by removing numerical suffix and prepending "if_" prefix. Whereas both tap and vmnet interfaces share the same if_tap.ko kernel module, and there is no seperate if_vmnet.ko one.

Possible workaround (successfully tested): during installkernel make a copy (or hardlink) of if_tap.ko under the name if_vmnet.ko, that works fine. By the way, it makes sense to hardlink tap(4) and vmnet(4) manual pages too.

Comment: I woudn't dare recommend suggested workaround as an ultimate solution because of possible unforeseen pitfalls (such as filesystems incapable of hardlinks etc.).

>Release-Note:
>Audit-Trail:
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