thanks for both hints - FFI looks interesting but I don’t want to wrap a
Funny that I missed the ‘p’ of pack - it’s working now:
Copied from wireless.h
SIOCGIWESSID = 0x8B1B
IW_ESSID_MAX_SIZE = 32
iwreq = [ “wlan0”, " " * IW_ESSID_MAX_SIZE, IW_ESSID_MAX_SIZE, 0
sock = Socket.new(Socket::AF_INET, Socket::SOCK_DGRAM, 0)
interface, essid, len, flags = iwreq.unpack(“a16pII”)
Now I can check if I can fetch the max. link quality via ioctl too.
---- On Tue, 22 Sep 2009 16:58:46 -0700 Joel VanderWerf
[email protected] wrote ----
Christoph K. wrote:
To avoid relying on the wireless tools I want to get the essid
directly from the device with ioctl, in C
this wouldn’t be a problem, but in Ruby it’s quite different.
The problem is following struct from wireless.h that is used as
input/reply of ioctl:
void __user pointer; / Pointer to the data (in user space) /
__u16 length; / number of fields or size in bytes /
__u16 flags; / Optional params */
The pointer part must be a valid address of a memory area, followed
by the length in bytes,
followed by a flag field. I tried with Array#pack and the
bit-struct gem, but haven’t found a solution yet.
Is there a way to bypass this memory pointer problem?
How are you calling ioctl() ? If you’re using FFI, then googling for
FFI::Pointer should help. If you’re calling it in some other way and
trying to access the binary data in ruby, does the P specifier in
vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407