Extended nameif matching

[Nico Erfurth]

Hi,

for my current project we needed a tool to rename interfaces by their
used usb-slot. While udev and ifrename (from the wireless-tools package)
 can manage this, they both would require additional space. After
watching at the nameif applet of busybox I decided to implement the
needed features here by extending its syntax a bit. The new feature can
be disabled in the config.

The new syntax for /etc/mactab looks like this:
eth3 bus=usb-0000:00:08.2-2 mac=00:80:C8:38:91:B5
eth4 bus=usb-0000:00:10.4-5 driver=asix
eth5 bus=usb-0000:00:08.2-1
eth7 00:80:C8:38:91:B5

the mac= selector is optional, everything unknown will be parsed as a
mac-address by default. So this should be backward compatible.

I've also changed the way nameif uses to discover devices. The used
method wasn't stable, because on a hotplug-system the if_index could
have "holes". Lets say you unplug an usb-device that previously had
if_index 4, if you replug it, it will get the next available, while
if_index 4 is unused. The old discovery method would stop scanning here
and not see interfaces beyond if_index 4. The new method relies on
parsing /proc/net/dev.


By refactoring the existing code I could keep the added size down.
w/o extended matching:
function                                             old     new   delta
new_ch                                                 -     157    +157
.rodata                                             1031    1023      -8
nameif_main                                          630     602     -28
cc_macaddr                                            51       -     -51
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 0/2 up/down: 157/-87)            Total: 70
bytes
   text    data     bss     dec     hex filename
   8233     413      60    8706    2202 busybox_old
   8469     425      60    8954    22fa busybox_unstripped


with extended matching:
function                                             old     new   delta
new_ch                                                 -     316    +316
nameif_main                                          630     764    +134
.rodata                                             1031    1066     +35
cc_macaddr                                            51       -     -51
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 2/0 up/down: 485/-51)           Total: 434
bytes
   text    data     bss     dec     hex filename
   8233     413      60    8706    2202 busybox_old
   8833     425      60    9318    2466 busybox_unstripped

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