Getting /dev entry by interface name

[Roman Bogorodskiy]

Hi,

I have the following scenario:

1. Create tap(4) like that:

# ifconfig tap create
tap2
#

2. Rename it

# ifconfig tap2 name testif
testif

Now I can do 'ifconfig testif' and there'll be no signs that it was
named 'tap2' previously, however, in /dev it's still /dev/tap2.

The question is: given that I didn't save the original name before
renaming, what are the ways to map 'testif' to its /dev entry (/dev/tap2
in our example)?

The only way I found so far is to iterate over /dev/tap*, calling
TAPGIFNAME and checking if result matches the name I'm trying to look
up. This approach doesn't look good for a number of reasons, main are:

1. It's inefficient, esp. if there are many tap(4) devices,
2. It has annoying side effects, such as if the interface was up, after
opening it it will be down (unless net.link.tap.up_on_open is set to 1,
which I don't want to rely on).

Is there a cleaner way maybe? I wasn't able to get this information via
data returned by getifaddrs(3) for example, but probably I'm missing
something.

Roman Bogorodskiy
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