From: Christoph Kappel <unexist@...>
Date: 2009-09-23T18:27:56+09:00
Subject: Re: Getting essid via ioctl

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Hey Joel,

thanks for both hints - FFI looks interesting but I don't want to wrap a li=
brary.=20
Funny that I missed the 'p' of pack - it's working now:

require "socket"

# Copied from wireless.h
SIOCGIWESSID      =3D 0x8B1B =20
IW_ESSID_MAX_SIZE =3D 32

iwreq =3D [ "wlan0", " " * IW_ESSID_MAX_SIZE, IW_ESSID_MAX_SIZE, 0 ].pack("=
a16pII")

sock =3D Socket.new(Socket::AF_INET, Socket::SOCK_DGRAM, 0)

sock.ioctl(SIOCGIWESSID, iwreq)

interface, essid, len, flags =3D iwreq.unpack("a16pII")

puts essid

Now I can check if I can fetch the max. link quality via ioctl too.

Wbr, Christoph

---- On Tue, 22 Sep 2009 16:58:46 -0700 Joel VanderWerf <vjoel@path.berkele=
y.edu> wrote ----=20

 > Christoph Kappel wrote:
 > > Hello.
 > >=20
 > > To avoid relying on the wireless tools I want to get the essid directl=
y from the device with ioctl, in C=20
 > > this wouldn't be a problem, but in Ruby it's quite different.
 > >=20
 > > The problem is following struct from wireless.h that is used as input/=
reply of ioctl:
 > >=20
 > > struct iw_point
 > > {
 > > void __user *pointer; /* Pointer to the data (in user space) */
 > > __u16 length; /* number of fields or size in bytes */
 > > __u16 flags; /* Optional params */
 > > };
 > >=20
 > > The pointer part must be a valid address of a memory area, followed by=
 the length in bytes,=20
 > > followed by a flag field. I tried with Array#pack and the bit-struct g=
em, but haven't found a solution yet.
 > >=20
 > > Is there a way to bypass this memory pointer problem?
 >=20
 > Christoph,
 >=20
 > How are you calling ioctl() ? If you're using FFI, then googling for=20
 > FFI::Pointer should help. If you're calling it in some other way and are=
=20
 > trying to access the binary data in ruby, does the P specifier in=20
 > pack/unpack work?
 >=20
 > --=20
 >  vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407
 >
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