Alfred Perlstein wrote:

> * Palle Lyckegaard <PalleLyckegaard@e-noerd.dk> [011121 14:40] wrote:
> > Hi,
> >
> > Just wondering if NetBSD (or any of the other BSDs) support the
> > PF_PACKET domain in the socket calls? I have been using this neat
> > feature on Linux and would like to have this on NetBSD as well if
> > possible.
>
> I find it sort of strange that people always seem to toss up
> $OBSCURE_LINUX_FEATURE as if we all know what it is.  I think that
> if you (and others) would include a URL or short description clearly
> documenting the "feature" you'd quickly gain more interest rather
> than having some of us (well at least me) think, "oh great another
> thing that should/could be done in userland or using existing
> facilities that Linux has made yet another kernel API for."

from the Linux 'man packet'... sorry - it's not really a short description..
:-)

------ start of man page -------------------------------

PACKET(7)           Linux Programmer's Manual           PACKET(7)

NAME
       packet, PF_PACKET - packet interface on device level.

SYNOPSIS
       #include <sys/socket.h>
       #include <features.h>    /* for the glibc version number */
       #if __GLIBC__ >= 2 && __GLIBC_MINOR >= 1
       #include <netpacket/packet.h>
       #include <net/ethernet.h>     /* the L2 protocols */
       #else
       #include <asm/types.h>
       #include <linux/if_packet.h>
       #include <linux/if_ether.h>   /* The L2 protocols */
       #endif

       packet_socket = socket(PF_PACKET, int socket_type, int protocol);

DESCRIPTION
       Packet  sockets  are used to receive or send raw packets at the
device driver (OSI Layer 2) level. They allow the user to implement protocol

       modules in user space on top of the physical layer.

       The socket_type is either SOCK_RAW for raw packets including the link
level header or SOCK_DGRAM for cooked  packets  with  the  link  level
       header  removed.  The  link  level header information is available in
a common format in a sockaddr_ll.  protocol is the IEEE 802.3 protocol
       number in network order. See the <linux/if_ether.h> include file for
a list of allowed protocols. When protocol is set  to  htons(ETH_P_ALL)
       then  all  protocols are received.  All incoming packets of that
protocol type will be passed to the packet socket before they are passed to
       the protocols implemented in the kernel.

       Only processes with effective uid 0 or the CAP_NET_RAW capability may
open packet sockets.

       SOCK_RAW packets are passed to and from the device driver without any
changes in the packet data.  When receiving a packet, the  address  is
       still  parsed  and  passed in a standard sockaddr_ll address
structure.  When transmitting a packet, the user supplied buffer should
contain
       the physical layer header.  That packet is then queued unmodified to
the network driver of the interface defined by the destination address.
       Some device drivers always add other headers.  SOCK_RAW is similar to
but not compatible with the obsolete SOCK_PACKET of Linux 2.0.

       SOCK_DGRAM  operates  on  a  slightly  higher  level.  The physical
header is removed before the packet is passed to the user.  Packets sent
       through a SOCK_DGRAM packet socket get a suitable physical layer
header based on the information  in  the  sockaddr_ll  destination  address
       before they are queued.

       By  default  all  packets  of  the  specified protocol type are
passed to a packet socket. To only get packets from a specific interface use

       bind(2) specifying an address in a struct sockaddr_ll to bind the
packet socket to an interface. Only the sll_protocol and  the  sll_ifindex
       address fields are used for purposes of binding.

       The connect(2) operation is not supported on packet sockets.

ADDRESS TYPES
       The sockaddr_ll is a device independent physical layer address.

              struct sockaddr_ll
              {
                  unsigned short  sll_family;    /* Always AF_PACKET */
                  unsigned short  sll_protocol;  /* Physical layer protocol
*/
                  int             sll_ifindex;   /* Interface number */
                  unsigned short  sll_hatype;    /* Header type */
                  unsigned char   sll_pkttype;   /* Packet type */
                  unsigned char   sll_halen;     /* Length of address */
                  unsigned char   sll_addr[8];   /* Physical layer address
*/
              };

       sll_protocol  is  the  standard ethernet protocol type in network
order as defined in the linux/if_ether.h include file.  sll_ifindex is the
       interface index of the interface (see netdevice(2) ); 0 matches any
interface (only legal for binding).  sll_hatype is a ARP type as defined
       in  the  linux/if_arp.h include file.  sll_pkttype contains the
packet type. Valid types are PACKET_HOST for a packet addressed to the local

       host, PACKET_BROADCAST for a physical layer broadcast packet,
PACKET_MULTICAST for a packet sent to  a  physical  layer  multicast
address,
       PACKET_OTHERHOST  for  a  packet  to  some other host that has been
caught by a device driver in promiscuous mode, and PACKET_OUTGOING for a
       packet originated from the local host that is looped back to a packet
socket. These types make  only  sense  for  receiving.   sll_addr  and
       sll_halen contain the physical layer (e.g. IEEE 802.3) address and
its length. The exact interpretation depends on the device.

SOCKET OPTIONS
       Packet  sockets  can  be  used  to configure physical layer
multicasting and promiscuous mode. It works by calling setsockopt(2) on a
packet
       socket for SOL_PACKET and one of the options PACKET_ADD_MEMBERSHIP to
add a binding or PACKET_DROP_MEMBERSHIP to drop it.  They both  expect
       a packet_mreq structure as argument:

              struct packet_mreq
              {
                  int             mr_ifindex;    /* interface index */
                  unsigned short  mr_type;       /* action */
                  unsigned short  mr_alen;       /* address length */
                  unsigned char   mr_address[8]; /* physical layer address
*/
              };

       mr_ifindex  contains  the interface index for the interface whose
status should be changed.  The mr_type parameter specifies which action to
       perform.  PACKET_MR_PROMISC enables receiving all packets on a shared
medium - often  known  as  ``promiscuous  mode'',  PACKET_MR_MULTICAST
       binds  the  socket  to  the physical layer multicast group specified
in mr_address and mr_alen, and PACKET_MR_ALLMULTI sets the socket up to
       receive all multicast packets arriving at the interface.

       In addition the traditional ioctls SIOCSIFFLAGS, SIOCADDMULTI,
SIOCDELMULTI can be used for the same purpose.

IOCTLS
       SIOCGSTAMP can be used to receive the time stamp of the last received
packet. Argument is a struct timeval.

       In addition all standard ioctls defined in netdevice(7) and socket(7)
are valid on packet sockets.

ERROR HANDLING
       Packet sockets do no error handling other than errors occurred while
passing the packet to the device driver. They don't have the concept of
       a pending error.

COMPATIBILITY
       In  Linux  2.0,  the  only  way  to  get a packet socket was by
calling socket(PF_INET, SOCK_PACKET, protocol).  This is still supported but

       strongly deprecated.  The main difference between the two methods is
that SOCK_PACKET uses the old struct sockaddr_pkt to specify an  inter­
       face, which doesn't provide physical layer independence.

              struct sockaddr_pkt
              {
                  unsigned short  spkt_family;
                  unsigned char   spkt_device[14];
                  unsigned short  spkt_protocol;
              };

       spkt_family  contains  the  device type, spkt_protocol is the IEEE
802.3 protocol type as defined in <sys/if_ether.h> and spkt_device is the
       device name as a null terminated string, e.g. eth0.

       This structure is obsolete and should not be used in new code.
NOTES
       For portable programs it is suggested to use PF_PACKET via pcap(3);
although this only covers a subset of the PF_PACKET features.

       The SOCK_DGRAM packet sockets make no attempt to create or parse the
IEEE 802.2 LLC header for a IEEE  802.3  frame.   When  ETH_P_802_3  is
       specified  as  protocol for sending the kernel creates the 802.3
frame and fills out the length field; the user has to supply the LLC header
       to get a fully conforming packet. Incoming 802.3 packets are not
multiplexed on the DSAP/SSAP protocol fields; instead they are supplied  to
       the  user as protocol ETH_P_802_2 with the LLC header prepended. It
is thus not possible to bind to ETH_P_802_3; bind to ETH_P_802_2 instead
       and do the protocol multiplex yourself.  The default for sending is
the standard Ethernet DIX encapsulation with the protocol filled in.

       Packet sockets are not subject to the input or output firewall
chains.

ERRORS
       ENETDOWN
              Interface is not up.

       ENOTCONN
              No interface address passed.

       ENODEV Unknown device name or interface index specified in interface
address.

       EMSGSIZE
              Packet is bigger than interface MTU.

       ENOBUFS
              Not enough memory to allocate the packet.

       EFAULT User passed invalid memory address.

       EINVAL Invalid argument.

       ENXIO  Interface address contained illegal interface index.

       EPERM  User has insufficient privileges to carry out this operation.

       EADDRNOTAVAIL
              Unknown multicast group address passed.

       ENOENT No packet received.

              In addition other errors may be generated by the low-level
driver.

VERSIONS
       PF_PACKET is a new feature in Linux 2.2. Earlier Linux versions
supported only SOCK_PACKET.

BUGS
       glibc 2.1 does not have a define for SOL_PACKET.  The suggested
workaround is to use
              #ifndef SOL_PACKET
              #define SOL_PACKET 263
              #endif
       This is fixed in later glibc versions and also does not occur on
libc5 systems.

       The IEEE 802.2/803.3 LLC handling could be considered as a bug.

       Socket filters are not documented.

CREDITS
       This man page was writen by Andi Kleen with help from Matthew
Wilcox.  PF_PACKET in Linux 2.2 was implemented by Alexey Kuznetsov, based
on
       code by Alan Cox and others.

SEE ALSO
       ip(7), socket(7), socket(2), raw(7), pcap(3).

       RFC 894 for the standard IP Ethernet encapsulation.

       RFC 1700 for the IEEE 802.3 IP encapsulation.

       The linux/if_ether.h include file for physical layer protocols.

Linux Man Page             29 Apr 1999                          1

------ end of man page -------------------------------

>
>
> > I've been looking at the man-pages for 'bfp' - it seems possible to use
> > the bpf-devices for both sending and receiving raw data link layer
> > frames - have anyone tried that?
>
> Yes.
>
> > Is it worth considering implementing the PF_PACKET on *BSD or can the
> > 'bpf' be used?
> >
> > It would be a nice place for me to start contributing to the *BSD
> > world...
>
> Yes, that would be nice, but before you possibly duplicate work
> already done, why not have a look at libpcap or some of the libraries
> that make packet capture and raw packet sending work on multiple
> OSes through a (mostly) transparent library.

sure - I'll dig more into this...


Thanks   :-)

Palle


>
>
> --
> -Alfred Perlstein [alfred@freebsd.org]
> 'Instead of asking why a piece of software is using "1970s technology,"
>  start asking why software is ignoring 30 years of accumulated wisdom.'
>                            http://www.morons.org/rants/gpl-harmful.php3