path: root/networking/using_networking_rtems_app.rst

Using Networking in an RTEMS Application
########################################

Makefile changes
================

Including the required managers
-------------------------------

The FreeBSD networking code requires several RTEMS managers
in the application:
.. code:: c

    MANAGERS = io event semaphore

Increasing the size of the heap
-------------------------------

The networking tasks allocate a lot of memory.  For most applications
the heap should be at least 256 kbytes.
The amount of memory set aside for the heap can be adjusted by setting
the ``CFLAGS_LD`` definition as shown below:
.. code:: c

    CFLAGS_LD += -Wl,--defsym -Wl,HeapSize=0x80000

This sets aside 512 kbytes of memory for the heap.

System Configuration
====================

The networking tasks allocate some RTEMS objects.  These
must be accounted for in the application configuration table.  The following
lists the requirements.

*TASKS*
    One network task plus a receive and transmit task for each device.

*SEMAPHORES*
    One network semaphore plus one syslog mutex semaphore if the application uses
    openlog/syslog.

*EVENTS*
    The network stack uses ``RTEMS_EVENT_24`` and ``RTEMS_EVENT_25``.
    This has no effect on the application configuration, but
    application tasks which call the network functions should not
    use these events for other purposes.

Initialization
==============

Additional include files
------------------------

The source file which declares the network configuration
structures and calls the network initialization function must include
.. code:: c

    #include <rtems/rtems_bsdnet.h>

Network Configuration
---------------------

The network configuration is specified by declaring
and initializing the ``rtems_bsdnet_config``
structure.
.. code:: c

    struct rtems_bsdnet_config {
    /*
    * This entry points to the head of the ifconfig chain.
    \*/
    struct rtems_bsdnet_ifconfig \*ifconfig;
    /*
    * This entry should be rtems_bsdnet_do_bootp if BOOTP
    * is being used to configure the network, and NULL
    * if BOOTP is not being used.
    \*/
    void                    (\*bootp)(void);
    /*
    * The remaining items can be initialized to 0, in
    * which case the default value will be used.
    \*/
    rtems_task_priority  network_task_priority;  /* 100        \*/
    unsigned long        mbuf_bytecount;         /* 64 kbytes  \*/
    unsigned long        mbuf_cluster_bytecount; /* 128 kbytes \*/
    char                \*hostname;               /* BOOTP      \*/
    char                \*domainname;             /* BOOTP      \*/
    char                \*gateway;                /* BOOTP      \*/
    char                \*log_host;               /* BOOTP      \*/
    char                \*name_server[3];         /* BOOTP      \*/
    char                \*ntp_server[3];          /* BOOTP      \*/
    unsigned long        sb_efficiency;          /* 2          \*/
    /* UDP TX: 9216 bytes \*/
    unsigned long        udp_tx_buf_size;
    /* UDP RX: 40 * (1024 + sizeof(struct sockaddr_in)) \*/
    unsigned long        udp_rx_buf_size;
    /* TCP TX: 16 * 1024 bytes \*/
    unsigned long        tcp_tx_buf_size;
    /* TCP TX: 16 * 1024 bytes \*/
    unsigned long        tcp_rx_buf_size;
    /* Default Network Tasks CPU Affinity \*/
    #ifdef RTEMS_SMP
    const cpu_set_t     \*network_task_cpuset;
    size_t               network_task_cpuset_size;
    #endif
    };

The structure entries are described in the following table.
If your application uses BOOTP/DHCP to obtain network configuration
information and if you are happy with the default values described
below, you need to provide only the first two entries in this structure.

``struct rtems_bsdnet_ifconfig \*ifconfig``

    A pointer to the first configuration structure of the first network
    device.  This structure is described in the following section.
    You must provide a value for this entry since there is no default value for it.

``void (\*bootp)(void)``

    This entry should be set to ``rtems_bsdnet_do_bootp`` if your
    application by default uses the BOOTP/DHCP client protocol to obtain
    network configuration information.  It should be set to ``NULL`` if
    your application does not use BOOTP/DHCP.
    You can also use ``rtems_bsdnet_do_bootp_rootfs`` to have a set of
    standard files created with the information return by the BOOTP/DHCP
    protocol. The IP address is added to :file:`/etc/hosts` with the host
    name and domain returned. If no host name or domain is returned``me.mydomain`` is used. The BOOTP/DHCP server's address is also
    added to :file:`/etc/hosts`. The domain name server listed in the
    BOOTP/DHCP information are added to :file:`/etc/resolv.conf`. A``search`` record is also added if a domain is returned. The files
    are created if they do not exist.
    The default ``rtems_bsdnet_do_bootp`` and``rtems_bsdnet_do_bootp_rootfs`` handlers will loop for-ever
    waiting for a BOOTP/DHCP server to respond. If an error is detected
    such as not valid interface or valid hardware address the target will
    reboot allowing any hardware reset to correct itself.
    You can provide your own custom handler which allows you to perform
    an initialization that meets your specific system requirements. For
    example you could try BOOTP/DHCP then enter a configuration tool if no
    server is found allowing the user to switch to a static configuration.

``int network_task_priority``
    The priority at which the network task and network device
    receive and transmit tasks will run.
    If a value of 0 is specified the tasks will run at priority 100.

``unsigned long mbuf_bytecount``
    The number of bytes to allocate from the heap for use as mbufs.
    If a value of 0 is specified, 64 kbytes will be allocated.

``unsigned long mbuf_cluster_bytecount``
    The number of bytes to allocate from the heap for use as mbuf clusters.
    If a value of 0 is specified, 128 kbytes will be allocated.

``char \*hostname``
    The host name of the system.
    If this, or any of the following, entries are ``NULL`` the value
    may be obtained from a BOOTP/DHCP server.

``char \*domainname``
    The name of the Internet domain to which the system belongs.

``char \*gateway``
    The Internet host number of the network gateway machine,
    specified in 'dotted decimal' (``129.128.4.1``) form.

``char \*log_host``
    The Internet host number of the machine to which ``syslog`` messages
    will be sent.

``char \*name_server[3]``
    The Internet host numbers of up to three machines to be used as
    Internet Domain Name Servers.

``char \*ntp_server[3]``
    The Internet host numbers of up to three machines to be used as
    Network Time Protocol (NTP) Servers.

``unsigned long sb_efficiency``
    This is the first of five configuration parameters related to
    the amount of memory each socket may consume for buffers.  The
    TCP/IP stack reserves buffers (e.g. mbufs) for each open socket.  The
    TCP/IP stack has different limits for the transmit and receive
    buffers associated with each TCP and UDP socket.  By tuning these
    parameters, the application developer can make trade-offs between
    memory consumption and performance.  The default parameters favor
    performance over memory consumption.  Seehttp://www.rtems.org/ml/rtems-users/2004/february/msg00200.html
    for more details but note that after the RTEMS 4.8 release series,
    the sb_efficiency default was changed from ``8`` to ``2``.
    The user should also be aware of the ``SO_SNDBUF`` and ``SO_RCVBUF``
    IO control operations.  These can be used to specify the
    send and receive buffer sizes for a specific socket.  There
    is no standard IO control to change the ``sb_efficiency`` factor.
    The ``sb_efficiency`` parameter is a buffering factor used
    in the implementation of the TCP/IP stack.  The default is ``2``
    which indicates double buffering.  When allocating memory for each
    socket, this number is multiplied by the buffer sizes for that socket.

``unsigned long udp_tx_buf_size``

    This configuration parameter specifies the maximum amount of
    buffer memory which may be used for UDP sockets to transmit
    with.  The default size is 9216 bytes which corresponds to
    the maximum datagram size.

``unsigned long udp_rx_buf_size``

    This configuration parameter specifies the maximum amount of
    buffer memory which may be used for UDP sockets to receive
    into.  The default size is the following length in bytes:

    .. code:: c

        40 * (1024 + sizeof(struct sockaddr_in)

``unsigned long tcp_tx_buf_size``

    This configuration parameter specifies the maximum amount of
    buffer memory which may be used for TCP sockets to transmit
    with.  The default size is sixteen kilobytes.

``unsigned long tcp_rx_buf_size``

    This configuration parameter specifies the maximum amount of
    buffer memory which may be used for TCP sockets to receive
    into.  The default size is sixteen kilobytes.

``const cpu_set_t \*network_task_cpuset``

    This configuration parameter specifies the CPU affinity of the
    network task. If set to ``0`` the network task can be scheduled on
    any CPU. Only available in SMP configurations.

``size_t network_task_cpuset_size``

    This configuration parameter specifies the size of the``network_task_cpuset`` used. Only available in SMP configurations.

In addition, the following fields in the ``rtems_bsdnet_ifconfig``
are of interest.

*int port*
    The I/O port number (ex: 0x240) on which the external Ethernet
    can be accessed.

*int irno*
    The interrupt number of the external Ethernet controller.

*int bpar*
    The address of the shared memory on the external Ethernet controller.

Network device configuration
----------------------------

Network devices are specified and configured by declaring and initializing a``struct rtems_bsdnet_ifconfig`` structure for each network device.

The structure entries are described in the following table.  An application
which uses a single network interface, gets network configuration information
from a BOOTP/DHCP server, and uses the default values for all driver
parameters needs to initialize only the first two entries in the
structure.

``char \*name``
    The full name of the network device.  This name consists of the
    driver name and the unit number (e.g. ``"scc1"``).
    The ``bsp.h`` include file usually defines RTEMS_BSP_NETWORK_DRIVER_NAME as
    the name of the primary (or only) network driver.

``int (\*attach)(struct rtems_bsdnet_ifconfig \*conf)``
    The address of the driver ``attach`` function.   The network
    initialization function calls this function to configure the driver and
    attach it to the network stack.
    The ``bsp.h`` include file usually defines RTEMS_BSP_NETWORK_DRIVER_ATTACH as
    the name of the  attach function of the primary (or only) network driver.

``struct rtems_bsdnet_ifconfig \*next``
    A pointer to the network device configuration structure for the next network
    interface, or ``NULL`` if this is the configuration structure of the
    last network interface.

``char \*ip_address``
    The Internet address of the device,
    specified in 'dotted decimal' (``129.128.4.2``) form, or ``NULL``
    if the device configuration information is being obtained from a
    BOOTP/DHCP server.

``char \*ip_netmask``
    The Internet inetwork mask of the device,
    specified in 'dotted decimal' (``255.255.255.0``) form, or ``NULL``
    if the device configuration information is being obtained from a
    BOOTP/DHCP server.

``void \*hardware_address``
    The hardware address of the device, or ``NULL`` if the driver is
    to obtain the hardware address in some other way (usually  by reading
    it from the device or from the bootstrap ROM).

``int ignore_broadcast``
    Zero if the device is to accept broadcast packets, non-zero if the device
    is to ignore broadcast packets.

``int mtu``
    The maximum transmission unit of the device, or zero if the driver
    is to choose a default value (typically 1500 for Ethernet devices).

``int rbuf_count``
    The number of receive buffers to use, or zero if the driver is to
    choose a default value

``int xbuf_count``
    The number of transmit buffers to use, or zero if the driver is to
    choose a default value
    Keep in mind that some network devices may use 4 or more
    transmit descriptors for a single transmit buffer.

A complete network configuration specification can be as simple as the one
shown in the following example.
This configuration uses a single network interface, gets
network configuration information
from a BOOTP/DHCP server, and uses the default values for all driver
parameters.
.. code:: c

    static struct rtems_bsdnet_ifconfig netdriver_config = {
    RTEMS_BSP_NETWORK_DRIVER_NAME,
    RTEMS_BSP_NETWORK_DRIVER_ATTACH
    };
    struct rtems_bsdnet_config rtems_bsdnet_config = {
    &netdriver_config,
    rtems_bsdnet_do_bootp,
    };

Network initialization
----------------------

The networking tasks must be started before any network I/O operations
can be performed. This is done by calling:

.. code:: c

    rtems_bsdnet_initialize_network ();

This function is declared in ``rtems/rtems_bsdnet.h``.
t returns 0 on success and -1 on failure with an error code
in ``errno``.  It is not possible to undo the effects of
a partial initialization, though, so the function can be
called only once irregardless of the return code.  Consequently,
if the condition for the failure can be corrected, the
system must be reset to permit another network initialization
attempt.

Application Programming Interface
=================================

The RTEMS network package provides almost a complete set of BSD network
services.  The network functions work like their BSD counterparts
with the following exceptions:

- A given socket can be read or written by only one task at a time.

- The ``select`` function only works for file descriptors associated
  with sockets.

- You must call ``openlog`` before calling any of the ``syslog`` functions.

- *Some of the network functions are not thread-safe.*
  For example the following functions return a pointer to a static
  buffer which remains valid only until the next call:

  ``gethostbyaddr``

  ``gethostbyname``

  ``inet_ntoa``

      (``inet_ntop`` is thread-safe, though).

- The RTEMS network package gathers statistics.

- Addition of a mechanism to "tap onto" an interface
  and monitor every packet received and transmitted.

- Addition of ``SO_SNDWAKEUP`` and ``SO_RCVWAKEUP`` socket options.

Some of the new features are discussed in more detail in the following
sections.

Network Statistics
------------------

There are a number of functions to print statistics gathered by
the network stack.
These function are declared in ``rtems/rtems_bsdnet.h``.

``rtems_bsdnet_show_if_stats``
    Display statistics gathered by network interfaces.

``rtems_bsdnet_show_ip_stats``
    Display IP packet statistics.

``rtems_bsdnet_show_icmp_stats``
    Display ICMP packet statistics.

``rtems_bsdnet_show_tcp_stats``
    Display TCP packet statistics.

``rtems_bsdnet_show_udp_stats``
    Display UDP packet statistics.

``rtems_bsdnet_show_mbuf_stats``
    Display mbuf statistics.

``rtems_bsdnet_show_inet_routes``
    Display the routing table.

Tapping Into an Interface
-------------------------

RTEMS add two new ioctls to the BSD networking code:
SIOCSIFTAP and SIOCGIFTAP.  These may be used to set and get a*tap function*.  The tap function will be called for every
Ethernet packet received by the interface.

These are called like other interface ioctls, such as SIOCSIFADDR.
When setting the tap function with SIOCSIFTAP, set the ifr_tap field
of the ifreq struct to the tap function.  When retrieving the tap
function with SIOCGIFTAP, the current tap function will be returned in
the ifr_tap field.  To stop tapping packets, call SIOCSIFTAP with a
ifr_tap field of 0.

The tap function is called like this:
.. code:: c

    int tap (struct ifnet \*, struct ether_header \*, struct mbuf \*)

The tap function should return 1 if the packet was fully handled, in
which case the caller will simply discard the mbuf.  The tap function
should return 0 if the packet should be passed up to the higher
networking layers.

The tap function is called with the network semaphore locked.  It must
not make any calls on the application levels of the networking level
itself.  It is safe to call other non-networking RTEMS functions.

Socket Options
--------------

RTEMS adds two new ``SOL_SOCKET`` level options for ``setsockopt`` and``getsockopt``: ``SO_SNDWAKEUP`` and ``SO_RCVWAKEUP``.  For both, the
option value should point to a sockwakeup structure.  The sockwakeup
structure has the following fields:
.. code:: c

    void    (\*sw_pfn) (struct socket \*, caddr_t);
    caddr_t sw_arg;

These options are used to set a callback function to be called when, for
example, there is
data available from the socket (``SO_RCVWAKEUP``) and when there is space
available to accept data written to the socket (``SO_SNDWAKEUP``).

If ``setsockopt`` is called with the ``SO_RCVWAKEUP`` option, and the``sw_pfn`` field is not zero, then when there is data
available to be read from
the socket, the function pointed to by the ``sw_pfn`` field will be
called.  A pointer to the socket structure will be passed as the first
argument to the function.  The ``sw_arg`` field set by the``SO_RCVWAKEUP`` call will be passed as the second argument to the function.

If ``setsockopt`` is called with the ``SO_SNDWAKEUP``
function, and the ``sw_pfn`` field is not zero, then when
there is space available to accept data written to the socket,
the function pointed to by the ``sw_pfn`` field
will be called.  The arguments passed to the function will be as with``SO_SNDWAKEUP``.

When the function is called, the network semaphore will be locked and
the callback function runs in the context of the networking task.
The function must be careful not to call any networking functions.  It
is OK to call an RTEMS function; for example, it is OK to send an
RTEMS event.

The purpose of these callback functions is to permit a more efficient
alternative to the select call when dealing with a large number of
sockets.

The callbacks are called by the same criteria that the select
function uses for indicating "ready" sockets. In Stevens *Unix
Network Programming* on page 153-154 in the section "Under what Conditions
Is a Descriptor Ready?" you will find the definitive list of conditions
for readable and writable that also determine when the functions are
called.

When the number of received bytes equals or exceeds the socket receive
buffer "low water mark" (default 1 byte) you get a readable callback. If
there are 100 bytes in the receive buffer and you only read 1, you will
not immediately get another callback. However, you will get another
callback after you read the remaining 99 bytes and at least 1 more byte
arrives. Using a non-blocking socket you should probably read until it
produces error  EWOULDBLOCK and then allow the readable callback to tell
you when more data has arrived.  (Condition 1.a.)

For sending, when the socket is connected and the free space becomes at
or above the "low water mark" for the send buffer (default 4096 bytes)
you will receive a writable callback. You don't get continuous callbacks
if you don't write anything. Using a non-blocking write socket, you can
then call write until it returns a value less than the amount of data
requested to be sent or it produces error EWOULDBLOCK (indicating buffer
full and no longer writable). When this happens you can
try the write again, but it is often better to go do other things and
let the writable callback tell you when space is available to send
again. You only get a writable callback when the free space transitions
to above the "low water mark" and not every time you
write to a non-full send buffer. (Condition 2.a.)

The remaining conditions enumerated by Stevens handle the fact that
sockets become readable and/or writable when connects, disconnects and
errors occur, not just when data is received or sent. For example, when
a server "listening" socket becomes readable it indicates that a client
has connected and accept can be called without blocking, not that
network data was received (Condition 1.c).

Adding an IP Alias
------------------

The following code snippet adds an IP alias:
.. code:: c

    void addAlias(const char \*pName, const char \*pAddr, const char \*pMask)
    {
    struct ifaliasreq      aliasreq;
    struct sockaddr_in    \*in;
    /* initialize alias request \*/
    memset(&aliasreq, 0, sizeof(aliasreq));
    sprintf(aliasreq.ifra_name, pName);
    /* initialize alias address \*/
    in = (struct sockaddr_in \*)&aliasreq.ifra_addr;
    in->sin_family = AF_INET;
    in->sin_len    = sizeof(aliasreq.ifra_addr);
    in->sin_addr.s_addr = inet_addr(pAddr);
    /* initialize alias mask \*/
    in = (struct sockaddr_in \*)&aliasreq.ifra_mask;
    in->sin_family = AF_INET;
    in->sin_len    = sizeof(aliasreq.ifra_mask);
    in->sin_addr.s_addr = inet_addr(pMask);
    /* call to setup the alias \*/
    rtems_bsdnet_ifconfig(pName, SIOCAIFADDR, &aliasreq);
    }

Thanks to `Mike Seirs <mailto:mikes@poliac.com>`_ for this example
code.

Adding a Default Route
----------------------

The function provided in this section is functionally equivalent to
the command ``route add default gw yyy.yyy.yyy.yyy``:
.. code:: c

    void mon_ifconfig(int argc, char \*argv[],  unsigned32 command_arg,
    bool verbose)
    {
    struct sockaddr_in  ipaddr;
    struct sockaddr_in  dstaddr;
    struct sockaddr_in  netmask;
    struct sockaddr_in  broadcast;
    char               \*iface;
    int                 f_ip        = 0;
    int                 f_ptp       = 0;
    int                 f_netmask   = 0;
    int                 f_up        = 0;
    int                 f_down      = 0;
    int                 f_bcast     = 0;
    int                 cur_idx;
    int                 rc;
    int                 flags;
    bzero((void*) &ipaddr, sizeof(ipaddr));
    bzero((void*) &dstaddr, sizeof(dstaddr));
    bzero((void*) &netmask, sizeof(netmask));
    bzero((void*) &broadcast, sizeof(broadcast));
    ipaddr.sin_len = sizeof(ipaddr);
    ipaddr.sin_family = AF_INET;
    dstaddr.sin_len = sizeof(dstaddr);
    dstaddr.sin_family = AF_INET;
    netmask.sin_len = sizeof(netmask);
    netmask.sin_family = AF_INET;
    broadcast.sin_len = sizeof(broadcast);
    broadcast.sin_family = AF_INET;
    cur_idx = 0;
    if (argc <= 1) {
    /* display all interfaces \*/
    iface = NULL;
    cur_idx += 1;
    } else {
    iface = argv[1];
    if (isdigit(\*argv[2])) {
    if (inet_pton(AF_INET, argv[2], &ipaddr.sin_addr) < 0) {
    printf("bad ip address: %s\\n", argv[2]);
    return;
    }
    f_ip = 1;
    cur_idx += 3;
    } else {
    cur_idx += 2;
    }
    }
    if ((f_down !=0) && (f_ip != 0)) {
    f_up = 1;
    }
    while(argc > cur_idx) {
    if (strcmp(argv[cur_idx], "up") == 0) {
    f_up = 1;
    if (f_down != 0) {
    printf("Can't make interface up and down\\n");
    }
    } else if(strcmp(argv[cur_idx], "down") == 0) {
    f_down = 1;
    if (f_up != 0) {
    printf("Can't make interface up and down\\n");
    }
    } else if(strcmp(argv[cur_idx], "netmask") == 0) {
    if ((cur_idx + 1) >= argc) {
    printf("No netmask address\\n");
    return;
    }
    if (inet_pton(AF_INET, argv[cur_idx+1], &netmask.sin_addr) < 0) {
    printf("bad netmask: %s\\n", argv[cur_idx]);
    return;
    }
    f_netmask = 1;
    cur_idx += 1;
    } else if(strcmp(argv[cur_idx], "broadcast") == 0) {
    if ((cur_idx + 1) >= argc) {
    printf("No broadcast address\\n");
    return;
    }
    if (inet_pton(AF_INET, argv[cur_idx+1], &broadcast.sin_addr) < 0) {
    printf("bad broadcast: %s\\n", argv[cur_idx]);
    return;
    }
    f_bcast = 1;
    cur_idx += 1;
    } else if(strcmp(argv[cur_idx], "pointopoint") == 0) {
    if ((cur_idx + 1) >= argc) {
    printf("No pointopoint address\\n");
    return;
    }
    if (inet_pton(AF_INET, argv[cur_idx+1], &dstaddr.sin_addr) < 0) {
    printf("bad pointopoint: %s\\n", argv[cur_idx]);
    return;
    }
    f_ptp = 1;
    cur_idx += 1;
    } else {
    printf("Bad parameter: %s\\n", argv[cur_idx]);
    return;
    }
    cur_idx += 1;
    }
    printf("ifconfig ");
    if (iface != NULL) {
    printf("%s ", iface);
    if (f_ip != 0) {
    char str[256];
    inet_ntop(AF_INET, &ipaddr.sin_addr, str, 256);
    printf("%s ", str);
    }
    if (f_netmask != 0) {
    char str[256];
    inet_ntop(AF_INET, &netmask.sin_addr, str, 256);
    printf("netmask %s ", str);
    }
    if (f_bcast != 0) {
    char str[256];
    inet_ntop(AF_INET, &broadcast.sin_addr, str, 256);
    printf("broadcast %s ", str);
    }
    if (f_ptp != 0) {
    char str[256];
    inet_ntop(AF_INET, &dstaddr.sin_addr, str, 256);
    printf("pointopoint %s ", str);
    }
    if (f_up != 0) {
    printf("up\\n");
    } else if (f_down != 0) {
    printf("down\\n");
    } else {
    printf("\\n");
    }
    }
    if ((iface == NULL) \|| ((f_ip == 0) && (f_down == 0) && (f_up == 0))) {
    rtems_bsdnet_show_if_stats();
    return;
    }
    flags = 0;
    if (f_netmask) {
    rc = rtems_bsdnet_ifconfig(iface, SIOCSIFNETMASK, &netmask);
    if (rc < 0) {
    printf("Could not set netmask: %s\\n", strerror(errno));
    return;
    }
    }
    if (f_bcast) {
    rc = rtems_bsdnet_ifconfig(iface, SIOCSIFBRDADDR, &broadcast);
    if (rc < 0) {
    printf("Could not set broadcast: %s\\n", strerror(errno));
    return;
    }
    }
    if (f_ptp) {
    rc = rtems_bsdnet_ifconfig(iface, SIOCSIFDSTADDR, &dstaddr);
    if (rc < 0) {
    printf("Could not set destination address: %s\\n", strerror(errno));
    return;
    }
    flags \|= IFF_POINTOPOINT;
    }
    /* This must come _after_ setting the netmask, broadcast addresses \*/
    if (f_ip) {
    rc = rtems_bsdnet_ifconfig(iface, SIOCSIFADDR, &ipaddr);
    if (rc < 0) {
    printf("Could not set IP address: %s\\n", strerror(errno));
    return;
    }
    }
    if (f_up != 0) {
    flags \|= IFF_UP;
    }
    if (f_down != 0) {
    printf("Warning: taking interfaces down is not supported\\n");
    }
    rc = rtems_bsdnet_ifconfig(iface, SIOCSIFFLAGS, &flags);
    if (rc < 0) {
    printf("Could not set interface flags: %s\\n", strerror(errno));
    return;
    }
    }
    void mon_route(int argc, char \*argv[],  unsigned32 command_arg,
    bool verbose)
    {
    int                cmd;
    struct sockaddr_in dst;
    struct sockaddr_in gw;
    struct sockaddr_in netmask;
    int                f_host;
    int                f_gw       = 0;
    int                cur_idx;
    int                flags;
    int                rc;
    memset(&dst, 0, sizeof(dst));
    memset(&gw, 0, sizeof(gw));
    memset(&netmask, 0, sizeof(netmask));
    dst.sin_len = sizeof(dst);
    dst.sin_family = AF_INET;
    dst.sin_addr.s_addr = inet_addr("0.0.0.0");
    gw.sin_len = sizeof(gw);
    gw.sin_family = AF_INET;
    gw.sin_addr.s_addr = inet_addr("0.0.0.0");
    netmask.sin_len = sizeof(netmask);
    netmask.sin_family = AF_INET;
    netmask.sin_addr.s_addr = inet_addr("255.255.255.0");
    if (argc < 2) {
    rtems_bsdnet_show_inet_routes();
    return;
    }
    if (strcmp(argv[1], "add") == 0) {
    cmd = RTM_ADD;
    } else if (strcmp(argv[1], "del") == 0) {
    cmd = RTM_DELETE;
    } else {
    printf("invalid command: %s\\n", argv[1]);
    printf("\\tit should be 'add' or 'del'\\n");
    return;
    }
    if (argc < 3) {
    printf("not enough arguments\\n");
    return;
    }
    if (strcmp(argv[2], "-host") == 0) {
    f_host = 1;
    } else if (strcmp(argv[2], "-net") == 0) {
    f_host = 0;
    } else {
    printf("Invalid type: %s\\n", argv[1]);
    printf("\\tit should be '-host' or '-net'\\n");
    return;
    }
    if (argc < 4) {
    printf("not enough arguments\\n");
    return;
    }
    inet_pton(AF_INET, argv[3], &dst.sin_addr);
    cur_idx = 4;
    while(cur_idx < argc) {
    if (strcmp(argv[cur_idx], "gw") == 0) {
    if ((cur_idx +1) >= argc) {
    printf("no gateway address\\n");
    return;
    }
    f_gw = 1;
    inet_pton(AF_INET, argv[cur_idx + 1], &gw.sin_addr);
    cur_idx += 1;
    } else if(strcmp(argv[cur_idx], "netmask") == 0) {
    if ((cur_idx +1) >= argc) {
    printf("no netmask address\\n");
    return;
    }
    f_gw = 1;
    inet_pton(AF_INET, argv[cur_idx + 1], &netmask.sin_addr);
    cur_idx += 1;
    } else {
    printf("Unknown argument\\n");
    return;
    }
    cur_idx += 1;
    }
    flags = RTF_STATIC;
    if (f_gw != 0) {
    flags \|= RTF_GATEWAY;
    }
    if (f_host != 0) {
    flags \|= RTF_HOST;
    }
    rc = rtems_bsdnet_rtrequest(cmd, &dst, &gw, &netmask, flags, NULL);
    if (rc < 0) {
    printf("Error adding route\\n");
    }
    }

Thanks to `Jay Monkman <mailto:jtm@smoothmsmoothie.com>`_ for this example
code.

Time Synchronization Using NTP
------------------------------

.. code:: c

    int rtems_bsdnet_synchronize_ntp (int interval, rtems_task_priority priority);

If the interval argument is 0 the routine synchronizes the RTEMS time-of-day
clock with the first NTP server in the rtems_bsdnet_ntpserve array and
returns.  The priority argument is ignored.

If the interval argument is greater than 0, the routine also starts an
RTEMS task at the specified priority and polls the NTP server every
'interval' seconds.  NOTE: This mode of operation has not yet been
implemented.

On successful synchronization of the RTEMS time-of-day clock the routine
returns 0.  If an error occurs a message is printed and the routine returns -1
with an error code in errno.
There is no timeout - if there is no response from an NTP server the
routine will wait forever.

.. COMMENT: Written by Eric Norum

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.