On Mon, 2010-08-16 at 15:06 -0400, Christopher Piggott wrote:
> Start building the message. First build an SSID list with one entry
> in it (empty string)
> struct nl_msg *ssids = nlmsg_alloc();
> nla_put_string(ssids, 0, "");
I think that has to be a 1 instead of 0, but I'm not entirely sure.
> Next build the scan request message:
> struct nl_msg *msg = nlmsg_alloc();
> int flags = 0;
> int cmd = NL80211_CMD_TRIGGER_SCAN;
> genlmsg_put(msg, 0, 0, genl_family_get_id(nl80211), 0, flags, cmd, 0);
> /* append our ssid list to this message as a nested message */
> nla_put_nested(msg, NL80211_ATTR_SCAN_SSIDS, ssids)
You're not telling it which interface should scan, this is handled
generically in iw.c, look for
NLA_PUT_U32(msg, NL80211_ATTR_IFINDEX, devidx);
> Finally I send the request:
> int rc = nl_send_auto_complete(sock, msg);
>
> From this I found out that 32 bytes were sent (seems reasonable).
> Unfortunately, what I get back is this:
> [HEADER] 16 octets
> .nlmsg_len = 52
> .nlmsg_type = 2 <ERROR>
> .nlmsg_flags = 0 <>
> .nlmsg_seq = 1282012377
> .nlmsg_pid = 30415
> [ERRORMSG] 20 octets
> .error = -22 "Invalid argument"
> [ORIGINAL MESSAGE] 16 octets
> .nlmsg_len = 16
> .nlmsg_type = 23 <0x17>
> .nlmsg_flags = 5 <REQUEST,ACK>
> .nlmsg_seq = 1282012377
> .nlmsg_pid = 30415
>
> so, even following what iw's "scan.c" does I have somehow pieced the
> request together incorrectly.
>
> Questions:
> 1. Am I doing something obviously wrong?
You're also missing the interface as above.
> 2. Is this even the interface I should be using to do this? (I need
> to scan for all access points on a specific "hidden" SSID to retrieve
> some information about their SNR. It's a type of "site survey"
> application for building contour maps of coverage).
Yes, it does make sense.
> I'm not sure what I'm doing next makes sense, either. After I send
> the scan request I wait 3 seconds then start reading like this:
> while(nl_recvmsgs(sock, callbacks) != 0)
> {
> printf("processed a result\n");
> }
>
> I have registered my callback earlier; this seems to work because I
> get the message (above) plus later an "Operation Not Supported"
> message. The operation is indeed supported, as it works with the
> iwlist and iw command line tools.
Maybe you should look at wpa_supplicant either for doing your thing, or
for the driver_nl80211.c code in it, which is more explicit than iw.
johannes
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