How to use ixp4xx_hss (or generic-hdlc?)

How to use ixp4xx_hss (or generic-hdlc?)

[Miguel Ángel Álvarez]

Hi.

Is there any kind of tutorials on using generic-hdlc interfaces? I
just want to make a simple point-to-point connection between two
devices using ixp4xx_hss. I would like the data to be packetized using
hdlc.

So... The questions are...
-  I suppose I should use sethdlc to configure the interface, but I am
not sure about the configuration except that I should set "hdlc"
protocol (I hope).
- Then I should "open" the interface. I am trying with "ifconfig hdlc0
up", but I obtain an "ifconfig: SIOCSIFFLAGS: Function not
implemented". As my previous use of net devices has been using
ethernet or wifi devices in an "IP world", I am not quite sure if
ifconfig should be used in this case.
- Then I hope that I should open a raw (SOCK_RAW) PF_PACKET socket
with protocol IPPROTO_RAW? I am not using IP, so this does not seem to
be the correct protocol, but...
- And the address to sendto the data? Should it be formed just using
the name of the interface or it requires more data?

Thanks. I know these should be really newbie questions, but I am
finding difficult to know how to manage a "serial" device using a
netdev interface.

Miguel Ángel Álvarez

Re: How to use ixp4xx_hss (or generic-hdlc?)

[Francois Romieu]

Miguel Ángel Álvarez <gotzoncabanes@gmail.com> :
[...]
> Is there any kind of tutorials on using generic-hdlc interfaces?

Google + ixp4xx_hss + sethdlc -> first entry

http://www.kernel.org/pub/linux/utils/net/hdlc/

The DSCC4 mini-HOWTO is rather old but it is imho a decent intro
if you are a bit lost.

-- 
Ueimor

Re: How to use ixp4xx_hss (or generic-hdlc?)

[Miguel Ángel Álvarez]

Hi and thanks for the answer.

On Thu, Nov 20, 2008 at 11:24 PM, Francois Romieu <romieu@fr.zoreil.com> wrote:
> Miguel Ángel Álvarez <gotzoncabanes@gmail.com> :
> [...]
>> Is there any kind of tutorials on using generic-hdlc interfaces?
>
> Google + ixp4xx_hss + sethdlc -> first entry

Ummm? Not for me at least. If I do that I only find my previous post
and some information about goramo platform in polish (made by
krzysztof.

>
> http://www.kernel.org/pub/linux/utils/net/hdlc/

Yes... I checked that in the beginning, and there is where I found the
need to use sethdlc and the basic processes. (By the way... I do not
have the problem in ifconfig-ing up the interface... I just were
forgetting to so "sethdlc hdlc0 hdlc" previously).
>
> The DSCC4 mini-HOWTO is rather old but it is imho a decent intro
> if you are a bit lost.
>

I also checked it, and I found it very illustrating. Good work of
Frantisek (based on yours and Krzysztof's).

I have also taken a look to the code of sethdlc to see how the socket
to the interface was set. He made "sock = socket(PF_INET, SOCK_DGRAM,
IPPROTO_IP);" which I suppose does not care a lot because sethdlc only
uses the socket to send ioctls, and not any data transfers.

However, in my case, I need to send data in a non-IP world using the
interface. So... Is this the way I should open the socket? Would this
encapsulate my data in hdlc before sending it to the interface?

if I open the socket using sock = socket(PF_PACKET, SOCK_RAW,
htons(ETH_P_ALL)); I can send data into the interface, but it is just
sent as raw data (which is logic).

So... yes... I am a bit lost in this point.

Thanks

Miguel Ángel Álvarez

Re: How to use ixp4xx_hss (or generic-hdlc?)

[Krzysztof Halasa]

"Miguel Ángel Álvarez" <gotzoncabanes@gmail.com> writes:

> I have also taken a look to the code of sethdlc to see how the socket
> to the interface was set. He made "sock = socket(PF_INET, SOCK_DGRAM,
> IPPROTO_IP);" which I suppose does not care a lot because sethdlc only
> uses the socket to send ioctls, and not any data transfers.

This is a bit different matter, though you may need it to get ifr_index.

> However, in my case, I need to send data in a non-IP world using the
> interface. So... Is this the way I should open the socket? Would this
> encapsulate my data in hdlc before sending it to the interface?
>
> if I open the socket using sock = socket(PF_PACKET, SOCK_RAW,
> htons(ETH_P_ALL)); I can send data into the interface, but it is just
> sent as raw data (which is logic).

It should be bit-stuffed and encapsulated in HDLC frames (flags etc),
assuming a real HDLC device.

You may need to prepend some headers, though.

The basic idea is:

        int sock;
        struct ifreq ifr;
        struct sockaddr_ll addr;

        strcpy(ifr.ifr_name, "hdlc0");
        if ((sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP)) < 0)
                error();
        if (ioctl(sock, SIOCGIFINDEX, &ifr))
                error();
        close(sock);

        if ((sock = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))) < 0)
                error();

        memset(&addr, 0, sizeof(addr));
        addr.sll_family = AF_PACKET;
        addr.sll_protocol = htons(ETH_P_ALL);
        addr.sll_ifindex = ifr.ifr_ifindex;
then:
        sendto(sock, packet_data, packet_size, 0, &addr, sizeof(addr)) < 0)

for RX:
        if (bind(sock, &addr, sizeof(addr)) < 0)
                error();
then:
        recvfrom(sock, buffer, max_packet_size, 0, &addr, &addr_len)
-- 
Krzysztof Halasa

Re: How to use ixp4xx_hss (or generic-hdlc?)

[Miguel Ángel Álvarez]

Hi

2008/11/22 Krzysztof Halasa <khc@pm.waw.pl>:
> "Miguel Ángel Álvarez" <gotzoncabanes@gmail.com> writes:
>
>> I have also taken a look to the code of sethdlc to see how the socket
>> to the interface was set. He made "sock = socket(PF_INET, SOCK_DGRAM,
>> IPPROTO_IP);" which I suppose does not care a lot because sethdlc only
>> uses the socket to send ioctls, and not any data transfers.
>
> This is a bit different matter, though you may need it to get ifr_index.
>
Sure. You are right.

>> However, in my case, I need to send data in a non-IP world using the
>> interface. So... Is this the way I should open the socket? Would this
>> encapsulate my data in hdlc before sending it to the interface?
>>
>> if I open the socket using sock = socket(PF_PACKET, SOCK_RAW,
>> htons(ETH_P_ALL)); I can send data into the interface, but it is just
>> sent as raw data (which is logic).
>
> It should be bit-stuffed and encapsulated in HDLC frames (flags etc),
> assuming a real HDLC device.
>
> You may need to prepend some headers, though.
>

I am not sure of having understood you. The buffer I send using sendto
should be just the payload and the generic-hdlc (or the hardware)
encapsulates it in an hdlc frame, or should I prepare the whole frame?

> The basic idea is:
>
>        int sock;
>        struct ifreq ifr;
>        struct sockaddr_ll addr;
>
>        strcpy(ifr.ifr_name, "hdlc0");
>        if ((sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP)) < 0)
>                error();
>        if (ioctl(sock, SIOCGIFINDEX, &ifr))
>                error();
>        close(sock);
>
>        if ((sock = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))) < 0)
>                error();
>
>        memset(&addr, 0, sizeof(addr));
>        addr.sll_family = AF_PACKET;
>        addr.sll_protocol = htons(ETH_P_ALL);
>        addr.sll_ifindex = ifr.ifr_ifindex;
> then:
>        sendto(sock, packet_data, packet_size, 0, &addr, sizeof(addr)) < 0)
>
> for RX:
>        if (bind(sock, &addr, sizeof(addr)) < 0)
>                error();
> then:
>        recvfrom(sock, buffer, max_packet_size, 0, &addr, &addr_len)

I took a little different approach, using the same PF_PACKET socket to
obtain the ifr_ifindex, but in any case using your method or "my"
method, and activating the debugging in ixp4xx_hss, when I do a two
byte (0x30 0x31) sendto, the traces in debug_pkt give me:

1970/01/01,00:00:47 (none) user.debug kernel: hdlc0: hss_hdlc_xmit(2)
<7> 30<7>31<7>

I cannot test the real hardware output in the lines at the moment, so
I do not know if this is what I was supposed to obtain, or not
(talking about the hdlc headers and trailers...).

Thanks

Miguel Ángel

Re: How to use ixp4xx_hss (or generic-hdlc?)

[Krzysztof Halasa]

"Miguel Ángel Álvarez" <gotzoncabanes@gmail.com> writes:

> I am not sure of having understood you. The buffer I send using sendto
> should be just the payload and the generic-hdlc (or the hardware)
> encapsulates it in an hdlc frame, or should I prepare the whole
> frame?

You sendto() the payload, but what is a payload?

With a normal HDLC hw driver, it (and the hardware) will generate the
flag sequences, will do bit-(de)stuffing, will calculate and check the
checksums, residual bits, aborts etc.

You usually have to add 32-bit header: u8 address (broadcast,
multicast, unicast) and control (such as unnumbered frame type), and
u16 protocol number (IPv4, IPv6 etc, LCP/IPCP, Cisco keepalive etc).
That's why it's called "raw HDLC", you're dealing with raw HDLC
packets.

> I took a little different approach, using the same PF_PACKET socket to
> obtain the ifr_ifindex, but in any case using your method or "my"
> method, and activating the debugging in ixp4xx_hss, when I do a two
> byte (0x30 0x31) sendto, the traces in debug_pkt give me:
>
> 1970/01/01,00:00:47 (none) user.debug kernel: hdlc0: hss_hdlc_xmit(2)
> <7> 30<7>31<7>

It should do just that (those '<7>' are weird, though).
-- 
Krzysztof Halasa

Re: How to use ixp4xx_hss (or generic-hdlc?)

[Miguel Ángel Álvarez]

Hi

2008/11/24 Krzysztof Halasa <khc@pm.waw.pl>:
> "Miguel Ángel Álvarez" <gotzoncabanes@gmail.com> writes:
>
>> I am not sure of having understood you. The buffer I send using sendto
>> should be just the payload and the generic-hdlc (or the hardware)
>> encapsulates it in an hdlc frame, or should I prepare the whole
>> frame?
>
> You sendto() the payload, but what is a payload?
>
> With a normal HDLC hw driver, it (and the hardware) will generate the
> flag sequences, will do bit-(de)stuffing, will calculate and check the
> checksums, residual bits, aborts etc.
>
> You usually have to add 32-bit header: u8 address (broadcast,
> multicast, unicast) and control (such as unnumbered frame type), and
> u16 protocol number (IPv4, IPv6 etc, LCP/IPCP, Cisco keepalive etc).
> That's why it's called "raw HDLC", you're dealing with raw HDLC
> packets.
>
You are right... I was being quite simplistic.

>> I took a little different approach, using the same PF_PACKET socket to
>> obtain the ifr_ifindex, but in any case using your method or "my"
>> method, and activating the debugging in ixp4xx_hss, when I do a two
>> byte (0x30 0x31) sendto, the traces in debug_pkt give me:
>>
>> 1970/01/01,00:00:47 (none) user.debug kernel: hdlc0: hss_hdlc_xmit(2)
>> <7> 30<7>31<7>
>
> It should do just that (those '<7>' are weird, though).

Yes... I do not know where they can from, but I am 100% sure it is
only representation of the printk.

Thanks a lot. Things are much clear now.

Miguel Ángel Álvarez

Re: How to use ixp4xx_hss (or generic-hdlc?)

[Krzysztof Halasa]

"Miguel Ángel Álvarez" <gotzoncabanes@gmail.com> writes:

> Is there any kind of tutorials on using generic-hdlc interfaces?

Not much, Documentation/networking/generic-hdlc.txt.

> I
> just want to make a simple point-to-point connection between two
> devices using ixp4xx_hss. I would like the data to be packetized using
> hdlc.
> -  I suppose I should use sethdlc to configure the interface, but I am
> not sure about the configuration except that I should set "hdlc"
> protocol (I hope).

Sure.

> - Then I should "open" the interface. I am trying with "ifconfig hdlc0
> up", but I obtain an "ifconfig: SIOCSIFFLAGS: Function not
> implemented". As my previous use of net devices has been using
> ethernet or wifi devices in an "IP world", I am not quite sure if
> ifconfig should be used in this case.

modprobe driver and maybe hdlc_raw
sethdlc hdlc0 hdlc
ifconfig hdlc0 up should work fine.

> - Then I hope that I should open a raw (SOCK_RAW) PF_PACKET socket
> with protocol IPPROTO_RAW? I am not using IP, so this does not seem to
> be the correct protocol, but...

Seems entirely correct.

> - And the address to sendto the data? Should it be formed just using
> the name of the interface or it requires more data?

No, all data is sent to the other end :-)

> Thanks. I know these should be really newbie questions, but I am
> finding difficult to know how to manage a "serial" device using a
> netdev interface.

Actually it's a bit different than normal async serial ports - HDLC
means packets.
-- 
Krzysztof Halasa