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Dhcpclient: Bootconf, Lease, bootp, dhcp, applycfg, removecfg - client's side of dynamic host configuration protocol


include "dhcp.m";   # sic
dhcpclient := load Dhcpclient Dhcpclient->PATH;
Bootconf, Lease: import dhcpclient;

Bootconf: adt {
    ip:      string;
    ipgw:    string;
    ipmask:  string;
    bootf:   string;
    bootip:  string;
    dhcpip:  string;
    siaddr:  string;
    serverid: string;
    sys:     string;
    dom:     string;
    lease:   int;
    options: array of array of byte;
    vendor:  array of array of byte;

    new:     fn(): ref Bootconf;
    get:     fn(c: self ref Bootconf, n: int): array of byte;
    getint:  fn(c: self ref Bootconf, n: int): int;
    getip:   fn(c: self ref Bootconf, n: int): string;
    getips:  fn(c: self ref Bootconf, n: int): list of string;
    gets:    fn(c: self ref Bootconf, n: int): string;
    put:     fn(c: self ref Bootconf, n: int, a: array of byte);
    putint:  fn(c: self ref Bootconf, n: int, v: int);
    putips:  fn(c: self ref Bootconf, n: int, ips: list of string);
    puts:    fn(c: self ref Bootconf, n: int, s: string);

Lease: adt {
    configs: chan of (ref Bootconf, string);

    release: fn(l: self ref Lease);

init:      fn();
tracing:   fn(debug: int);
bootp:     fn(net: string, ctlifc: ref Sys->FD, device: string,
               init: ref Bootconf): (ref Bootconf, string);
dhcp:      fn(net: string, ctlifc: ref Sys->FD, device: string,
               init: ref Bootconf, options: array of int):
               (ref Bootconf, ref Lease, string);

applycfg:  fn(net: string, ctlifc: ref Sys->FD,
               conf: ref Bootconf): string;
removecfg: fn(net: string, ctlifc: ref Sys->FD,
               conf: ref Bootconf): string;


Dhcpclient implements the client side of the Dynamic Host Configuration Protocol (DHCP) of Internet RFC2131. In the interface, Internet addresses are represented as strings, in forms that ip(2) can parse, and that can be written directly to control files in ip(3).

Init must be called before invoking any other operation of the module.

Bootp reserves the UDP port on net for use by BOOTP/DHCP clients, and sends a BOOTP request (ie, one without a DHCP operation code). Net is the name of the network directory (if nil, the default is /net). If bootp is to configure the interface according to the results received, ctlifc should be open on the control file of the net/ipifc directory for the interface to be configured; otherwise it should be nil. Bootp repeats the request periodically until it either receives a reply or has made 5 attempts. It returns a tuple (conf, err). If it has received a reply, conf refers to a Bootconf value that contains the values received, and err is nil. If ctlifc is not nil, the interface will also have been configured appropriately. If a valid reply has not been received, or some other error occurred, conf is nil, and err is a diagnostic.

Dhcp has a similar interface, but runs the full DHCP protocol. The options array has integers representing possible DHCP options; dhcp asks the server to provide values for them. If options is nil, a few option values are requested that might be useful for Inferno (eg, subnet mask, gateway, DNS server, authentication and file servers, and so on). If the server does supply them, they can be retrieved either from specific fields of Bootconf, or using its get operations. Init is also usually nil, but can refer to a Bootconf that provides some values to suggest to the server, for instance if the client knows a previously-assigned address stored in non-volatile memory. Dhcp returns a tuple (conf, lease, err), where conf and err are just as for bootp, and the new component lease is a reference to a Lease value that gives access to the state of the client's address assignment.

DHCP allows a server to assign a client an address permanently, or to lease it for a specified time. In the latter case, Bootconf.lease will have a non-zero value, and the client must periodically renew the lease to retain the address, and dhcp creates a process to do so. The Lease value provides a way for that process to communicate changes (if any) to the network configuration. Each time the configuration changes, the process will send a message on the channel configs. (The channel is buffered, and dhcp first discards any previous notifications not yet received, so there are no ill effects if no process ever receives from the channel.) Each message is a tuple (conf, diag). If a new state change has been made successfully, conf refers to a Bootconf value with the details. Otherwise, conf is nil and diag explains what went wrong. In any case, the watchdog process continues to try to extend the lease, or failing that, obtain a new network configuration, perhaps from another server. Lease.release may be called to release the leased address and stop the watchdog.

Bootconf has the following operations:

Return a reference to a Bootconf with values initialised to nil or 0.
Return the value of DHCP option n as a raw array of bytes. Return nil if the option is not set.
Return the value of option n interpreted as an integer. Return zero if the option is not set.
Return the first Internet address provided for option n.
Return a list of all the Internet addresses provided for option n.
Return the value of option n as a string.
bc.put(n, a)
Set the value of DHCP option n to the bytes of byte array a. If a is nil, put removes any existing value for the option.
bc.putint(n, v)
Set option n to the integer value v.
bc.putips(n, ips)
Set option n to the list of Internet addresses ips.
bc.puts(n, s)
Set option n to the string n.

Dhcpclient names a few constants representing commonly-used configuration options (attributes). They are suitable parameters for the option selector n of Bootconf's get and put functions. The first set of constants name options for both BOOTP and DHCP:

Internet address(es) of Domain Name Servers
Current domain (see Bootconf.dom)
Host name (see Bootconf.sys)
Network mask (IPv4). Also see Bootconf.ipmask.
NetBIOS servers
Network Time Protocol servers
POP3 mail servers
Default router for subnet (see Bootconf.ipgw)
SMTP mail delivery servers
Vendor-specific data (see below)
HTTP proxy

The second set has DHCP options:

Name of the file containing a kernel for the client to load (eg, by TFTP); see Bootconf.bootf.
Lease time for IP address, in seconds (also see Bootconf.lease)
Maximum DHCP size the client is willing to accept (minimum 576 bytes).
Time interval in seconds from address assignment to the time address must be rebound.
Time interval in seconds from address assignment to first attempt to renew the address.
TFTP server from which to fetch kernel and parameter files; see Bootconf.bootip.
Identify vendor type and configuration of client. Inferno sets this to plan9_386 (sic) to encourage Plan 9 DHCP servers to respond; other servers will ignore it.

The final set give vendor-specific options that Inferno shares with Plan 9:

Flag OR'd in to an option number to mark it as destined for the `vendor information' section.
Authentication server (Ovendor|129)
File server (Ovendor|128)

Given a network configuration in conf, and a valid file descriptor for a network interface's control file, in the network net, applycfg sets the basic interface parameters (address, network mask, default gateway), and writes other parameters to net/ndb; conversely, removecfg removes from the interface just those parameters set by conf. Normally these functions are called automatically, as required, by dhcp and its watchdog process.




bootpd(8), dhcp(8)

DHCPCLIENT(2 ) Rev:  Thu Feb 15 14:43:27 GMT 2007