path: root/lib/inets/doc/src/tftp.xml

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>2006</year><year>2013</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.
    
    </legalnotice>

    <title>tftp</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
  </header>
  <module>tftp</module>
  <modulesummary>Trivial FTP</modulesummary>
  <description>
    <p>This is a complete implementation of the following IETF standards:</p>
    <list type="bulleted">
      <item>RFC 1350, The TFTP Protocol (revision 2).</item>
      <item>RFC 2347, TFTP Option Extension.</item>
      <item>RFC 2348, TFTP Blocksize Option.</item>
      <item>RFC 2349, TFTP Timeout Interval and Transfer Size Options.</item>
    </list>
    <p>The only feature that not is implemented in this release is
      the "netascii" transfer mode.</p>
    <p>The <seealso marker="#start/1">start/1</seealso> function starts
      a daemon process which listens for UDP packets on a port. When it
      receives a request for read or write it spawns a temporary server
      process which handles the actual transfer of the file.</p>
    <p>On the client side
      the <seealso marker="#read_file/3">read_file/3</seealso>
      and <seealso marker="#write_file/3">write_file/3</seealso>
      functions spawns a temporary client process which establishes
      contact with a TFTP daemon and performs the actual transfer of
      the file.</p>
    <p><c>tftp</c> uses a callback module to handle the actual file
      transfer. Two such callback modules are provided,
      <c>tftp_binary</c> and <c>tftp_file</c>. See
      <seealso marker="#read_file/3">read_file/3</seealso> and
      <seealso marker="#write_file/3">write_file/3</seealso> for
      more information about these. The user can also implement own
      callback modules, see <seealso marker="#tftp_callback">CALLBACK FUNCTIONS</seealso> below. A callback module provided by
      the user is registered using the <c>callback</c> option, see
      <seealso marker="#options">DATA TYPES</seealso> below.</p>
  </description>
  
 <section>
    <title>TFTP SERVER SERVICE START/STOP </title>
    
    <p>A TFTP server can be configured to start statically when starting
      the Inets application. Alternatively it can be started dynamically
      (when Inets already is started) by calling the Inets application API
      <c>inets:start(tftpd, ServiceConfig)</c>, or
      <c>inets:start(tftpd, ServiceConfig, How)</c>,
      see <seealso marker="inets">inets(3)</seealso> for details.
      The <c>ServiceConfig</c> for TFTP is described below in
      the <seealso marker="#options">COMMON DATA TYPES</seealso>
      section.</p>
    
    <p>The TFTP server can be stopped using <c>inets:stop(tftpd, Pid)</c>,
      see <seealso marker="inets">inets(3)</seealso> for details.</p>

    <p>The TPFT client is of such a temporary nature that it is not
      handled as a service in the Inets service framework.</p>
    
  </section>
  
  <section>
    <marker id="options"></marker>
    <title>COMMON DATA TYPES</title>
    <pre>
      ServiceConfig = Options
      Options = [option()]
      option() -- see below
    </pre>
    <p>Most of the options are common for both the client and the server
      side, but some of them differs a little. Here are the available
      options:</p>
    <taglist>
      <tag><c>{debug, Level}</c></tag>
      <item>
        <p><c>Level = none | error | warning | brief | normal | verbose | all</c></p>
        <p>Controls the level of debug printouts. The default is
          <c>none</c>.</p>
      </item>
      <tag><c>{host, Host}</c></tag>
      <item>
        <p><c>Host = hostname()</c> see
          <seealso marker="kernel:inet">inet(3)</seealso></p>
        <p>The name or IP address of the host where the TFTP daemon
          resides. This option is only used by the client.</p>
      </item>
      <tag><c>{port, Port}</c></tag>
      <item>
        <p><c>Port = int()</c></p>
        <p>The TFTP port where the daemon listens. It defaults to
          the standardized number 69. On the server side it may
          sometimes make sense to set it to 0, which means that
          the daemon just will pick a free port (which one is
          returned by the <c>info/1</c> function).</p>
        <p>If a socket has somehow already has been connected, the
          {udp, [{fd, integer()}]} option can be used to pass the
          open file descriptor to gen_udp. This can be automated
          a bit by using a command line argument stating the
          prebound file descriptor number. For example, if the
          Port is 69 and the file descriptor 22 has been opened by
          setuid_socket_wrap. Then the command line argument
          "-tftpd_69 22" will trigger the prebound file
          descriptor 22 to be used instead of opening port 69.
          The UDP option {udp, [{fd, 22}]} automatically be added.
          See init:get_argument/ about command line arguments and
          gen_udp:open/2 about UDP options.</p>
      </item>
      <tag><c>{port_policy, Policy}</c></tag>
      <item>
        <p><c>Policy = random | Port | {range, MinPort, MaxPort}</c>          <br></br>
<c>Port = MinPort = MaxPort = int()</c></p>
        <p>Policy for the selection of the temporary port which is used
          by the server/client during the file transfer. It defaults to
          <c>random</c> which is the standardized policy. With this
          policy a randomized free port used. A single port or a range
          of ports can be useful if the protocol should pass through a
          firewall.</p>
      </item>
      <tag><c>{udp, Options}</c></tag>
      <item>
        <p><c>Options = [Opt]</c> see
          <seealso marker="kernel:gen_udp#open/1">gen_udp:open/2</seealso></p>
      </item>
      <tag><c>{use_tsize, Bool}</c></tag>
      <item>
        <p><c>Bool = bool()</c></p>
        <p>Flag for automated usage of the <c>tsize</c> option. With
          this set to true, the <c>write_file/3</c> client will
          determine the filesize and send it to the server as
          the standardized <c>tsize</c> option. A <c>read_file/3</c>
          client will just acquire filesize from the server by sending
          a zero <c>tsize</c>.</p>
      </item>
      <tag><c>{max_tsize, MaxTsize}</c></tag>
      <item>
        <p><c>MaxTsize = int() | infinity</c></p>
        <p>Threshold for the maximal filesize in bytes. The transfer
          will be aborted if the limit is exceeded. It defaults to
          <c>infinity</c>.</p>
      </item>
      <tag><c>{max_conn, MaxConn}</c></tag>
      <item>
        <p><c>MaxConn = int() | infinity</c></p>
        <p>Threshold for the maximal number of active connections.
          The daemon will reject the setup of new connections if
          the limit is exceeded. It defaults to <c>infinity</c>.</p>
      </item>
      <tag><c>{TftpKey, TftpVal}</c></tag>
      <item>
        <p><c>TftpKey = string()</c>          <br></br>
<c>TftpVal = string()</c></p>
        <p>The name and value of a TFTP option.</p>
      </item>
      <tag><c>{reject, Feature}</c></tag>
      <item>
        <p><c>Feature = Mode | TftpKey</c>          <br></br>
<c>&nbsp;Mode = read | write</c>          <br></br>
<c>&nbsp;TftpKey = string()</c></p>
        <p>Control which features that should be rejected. This is
          mostly useful for the server as it may restrict usage of
          certain TFTP options or read/write access.</p>
      </item>
      <tag><c>{callback, {RegExp, Module, State}}</c></tag>
      <item>
        <p><c>RegExp = string()</c>          <br></br>
<c>Module = atom()</c>          <br></br>
<c>State  = term()</c></p>
        <p>Registration of a callback module. When a file is to be
          transferred, its local filename will be matched to the regular
          expressions of the registered callbacks. The first matching
          callback will be used the during the transfer. See
          <seealso marker="#read_file/3">read_file/3</seealso> and
          <seealso marker="#write_file/3">write_file/3</seealso>.
          </p>
        <p>The callback module must implement the <c>tftp</c> behavior,
          <seealso marker="#tftp_callback">CALLBACK FUNCTIONS</seealso>.</p>
      </item>

   <tag><c>{logger, Module}</c></tag>
      <item>
        <p><c>Module = module()()</c></p>

        <p>Callback module for customized logging of error, warning and
	  info messages. >The callback module must implement the
	  <c>tftp_logger</c> behavior,
          <seealso marker="#tftp_logger">LOGGER FUNCTIONS</seealso>.
          The default module is <c>tftp_logger</c>.</p>
      </item>

      <tag><c>{max_retries, MaxRetries}</c></tag>
      <item>
        <p><c>MaxRetries = int()</c></p>

        <p>Threshold for the maximal number of retries. By default
	  the server/client will try to resend a message up to
	  <c>5</c> times when the timeout expires.</p>
      </item>
    </taglist>

    <marker id="start1"></marker>
  </section>

  <funcs>
    <func>
      <name>start(Options) -> {ok, Pid} | {error, Reason}</name>
      <fsummary>Start a daemon process</fsummary>
      <type>
        <v>Options = [option()]</v>
        <v>Pid = pid()</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Starts a daemon process which listens for udp packets on a
	port. When it receives a request for read or write it spawns
	a temporary server process which handles the actual transfer
	of the (virtual) file.</p>
	
	<marker id="read_file"></marker>
      </desc>
    </func>

    <func>
      <name>read_file(RemoteFilename, LocalFilename, Options) -> {ok, LastCallbackState} | {error, Reason}</name>
      <fsummary>Read a (virtual) file from a TFTP server</fsummary>
      <type>
        <v>RemoteFilename = string()</v>
        <v>LocalFilename = binary | string()</v>
        <v>Options = [option()]</v>
        <v>LastCallbackState = term()</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Reads a (virtual) file <c>RemoteFilename</c> from a TFTP
	server.</p>
	<p>If <c>LocalFilename</c> is the atom <c>binary</c>,
	<c>tftp_binary</c> is used as callback module. It concatenates
	all transferred blocks and returns them as one single binary
	in <c>LastCallbackState</c>.</p>
	<p>If <c>LocalFilename</c> is a string and there are no
	registered callback modules, <c>tftp_file</c> is used as
	callback module. It writes each transferred block to the file
	named <c>LocalFilename</c> and returns the number of
	transferred bytes in <c>LastCallbackState</c>.</p>
	<p>If <c>LocalFilename</c> is a string and there are registered
	callback modules, <c>LocalFilename</c> is tested against
	the regexps of these and the callback module corresponding to
	the first match is used, or an error tuple is returned if no
	matching regexp is found.</p>
      </desc>
	
      <marker id="write_file"></marker>
    </func>

    <func>
      <name>write_file(RemoteFilename, LocalFilename, Options) -> {ok, LastCallbackState} | {error, Reason}</name>
      <fsummary>Write a (virtual) file to a TFTP server</fsummary>
      <type>
        <v>RemoteFilename = string()</v>
        <v>LocalFilename = binary() | string()</v>
        <v>Options = [option()]</v>
        <v>LastCallbackState = term()</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Writes a (virtual) file <c>RemoteFilename</c> to a TFTP
          server.</p>
        <p>If <c>LocalFilename</c> is a binary, <c>tftp_binary</c> is
          used as callback module. The binary is transferred block by
          block and the number of transferred bytes is returned in
          <c>LastCallbackState</c>.</p>
        <p>If <c>LocalFilename</c> is a string and there are no
          registered callback modules, <c>tftp_file</c> is used as
          callback module. It reads the file named <c>LocalFilename</c>
          block by block and returns the number of transferred bytes
          in <c>LastCallbackState</c>.</p>
        <p>If <c>LocalFilename</c> is a string and there are registered
	callback modules, <c>LocalFilename</c> is tested against
	the regexps of these and the callback module corresponding to
	the first match is used, or an error tuple is returned if no
	matching regexp is found.</p>
	
	<marker id="info_daemons"></marker>
      </desc>
    </func>

    <func>
      <name>info(daemons) -> [{Pid, Options}]</name>
      <fsummary>Return information about all daemons</fsummary>
      <type>
        <v>Pid = [pid()()]</v>
        <v>Options = [option()]</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Returns info about all TFTP daemon processes. </p>
	
	<marker id="info_servers"></marker>
      </desc>
    </func>

    <func>
      <name>info(servers) -> [{Pid, Options}]</name>
      <fsummary>Return information about all servers</fsummary>
      <type>
        <v>Pid = [pid()()]</v>
        <v>Options = [option()]</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Returns info about all TFTP server processes. </p>
	
	<marker id="info_pid"></marker>
      </desc>
    </func>

    <func>
      <name>info(Pid) -> {ok, Options} | {error, Reason}</name>
      <fsummary>Return information about a daemon, server or client process</fsummary>
      <type>
        <v>Options = [option()]</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Returns info about a TFTP daemon, server or client process.</p>
	
	<marker id="change_config_daemons"></marker>
      </desc>
    </func>

   <func>
      <name>change_config(daemons, Options) -> [{Pid, Result}]</name>
      <fsummary>Changes config for all daemons
      </fsummary>
      <type>
        <v>Options = [option()]</v>
        <v>Pid = pid()</v>
        <v>Result = ok | {error, Reason}</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Changes config for all TFTP daemon processes. </p>
	
	<marker id="change_config_servers"></marker>
      </desc>
    </func>

    <func>
      <name>change_config(servers, Options) -> [{Pid, Result}]</name>
      <fsummary>Changes config for all servers
      </fsummary>
      <type>
        <v>Options = [option()]</v>
        <v>Pid = pid()</v>
        <v>Result = ok | {error, Reason}</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Changes config for all TFTP server processes. </p>
	
	<marker id="change_config_pid"></marker>
      </desc>
    </func>

    <func>
      <name>change_config(Pid, Options) -> Result</name>
      <fsummary>Changes config for a TFTP daemon, server or client process</fsummary>
      <type>
        <v>Pid = pid()</v>
        <v>Options = [option()]</v>
        <v>Result = ok | {error, Reason}</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Changes config for a TFTP daemon, server or client process</p>
	
	<marker id="start2"></marker>
      </desc>
    </func>

    <func>
      <name>start() -> ok | {error, Reason}</name>
      <fsummary>Start the Inets application</fsummary>
      <type>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Starts the Inets application.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <marker id="tftp_callback"></marker>
    <title>CALLBACK FUNCTIONS</title>
    <p>A <c>tftp</c> callback module should be implemented as a
      <c>tftp</c> behavior and export the functions listed below.</p>
    <p>On the server side the callback interaction starts with a call to
      <c>open/5</c> with the registered initial callback state.
      <c>open/5</c> is expected to open the (virtual) file. Then either
      the <c>read/1</c> or <c>write/2</c> functions are invoked
      repeatedly, once per transferred block. At each function call
      the state returned from the previous call is obtained. When
      the last block has been encountered the <c>read/1</c> or
      <c>write/2</c> functions is expected to close the (virtual) file
      and return its last state. The <c>abort/3</c> function is only
      used in error situations. <c>prepare/5</c> is not used on
      the server side.</p>
    <p>On the client side the callback interaction is the same, but it
      starts and ends a bit differently. It starts with a call to
      <c>prepare/5</c> with the same arguments as <c>open/5</c> takes.
      <c>prepare/5</c> is expected to validate the TFTP options,
      suggested by the user and return the subset of them that it
      accepts. Then the options is sent to the server which will perform
      the same TFTP option negotiation procedure. The options that are
      accepted by the server are forwarded to the <c>open/5</c> function
      on the client side. On the client side the <c>open/5</c> function
      must accept all option as is or reject the transfer. Then
      the callback interaction follows the same pattern as described
      above for the server side. When the last block is encountered in
      <c>read/1</c> or <c>write/2</c> the returned state is forwarded to
      the user and returned from <c>read_file</c>/3 or
      <c>write_file/3</c>.</p>

    <p> If a callback (which performs the file access
    in the TFTP server) takes too long time (more than
    the double TFTP timeout), the server will abort the
    connection and send an error reply to the client.
    This implies that the server will release resources
    attached to the connection faster than before. The
    server simply assumes that the client has given
    up.</p>

    <p>If the TFTP server receives yet another request from
    the same client (same host and port) while it
    already has an active connection to the client, it
    will simply ignore the new request if the request is
    equal with the first one (same filename and options).
    This implies that the (new) client will be served
    by the already ongoing connection on the server
    side. By not setting up yet another connection, in
    parallel with the ongoing one, the server will
    consumer lesser resources. </p>
    
    <marker id="prepare"></marker>
  </section>

  <funcs>
    <func>
      <name>prepare(Peer, Access, Filename, Mode, SuggestedOptions, InitialState) -> {ok, AcceptedOptions, NewState} | {error, {Code, Text}}</name>
      <fsummary>Prepare to open a file on the client side</fsummary>
      <type>
        <v>Peer = {PeerType, PeerHost, PeerPort}</v>
        <v>PeerType = inet | inet6</v>
        <v>PeerHost = ip_address()</v>
        <v>PeerPort = integer()</v>
        <v>Access = read | write</v>
        <v>Filename = string()</v>
        <v>Mode = string()</v>
        <v>SuggestedOptions = AcceptedOptions = [{Key, Value}]</v>
        <v>&nbsp;Key = Value = string()</v>
        <v>InitialState = [] | [{root_dir, string()}]</v>
        <v>NewState = term()</v>
        <v>Code = undef | enoent | eacces | enospc</v>
        <v>&nbsp;&nbsp;| badop | eexist | baduser | badopt</v>
        <v>&nbsp;&nbsp;| int()</v>
        <v>Text = string()</v>
      </type>
      <desc>
	<p>Prepares to open a file on the client side.</p>
	<p>No new options may be added, but the ones that are present in
	<c>SuggestedOptions</c> may be omitted or replaced with new
	values in <c>AcceptedOptions</c>.</p>
	<p>Will be followed by a call to <c>open/4</c> before any
	read/write access is performed. <c>AcceptedOptions</c> is
	sent to the server which replies with those options that it
	accepts. These will be forwarded to <c>open/4</c> as
	<c>SuggestedOptions</c>.</p>
    
	<marker id="open"></marker>
      </desc>
    </func>

    <func>
      <name>open(Peer, Access, Filename, Mode, SuggestedOptions, State) -> {ok, AcceptedOptions, NewState} | {error, {Code, Text}}</name>
      <fsummary>Open a file for read or write access</fsummary>
      <type>
        <v>Peer = {PeerType, PeerHost, PeerPort}</v>
        <v>PeerType = inet | inet6</v>
        <v>PeerHost = ip_address()</v>
        <v>PeerPort = integer()</v>
        <v>Access = read | write</v>
        <v>Filename = string()</v>
        <v>Mode = string()</v>
        <v>SuggestedOptions = AcceptedOptions = [{Key, Value}]</v>
        <v>&nbsp;Key = Value = string()</v>
        <v>State = InitialState | term()</v>
        <v>&nbsp;InitialState = [] | [{root_dir, string()}]</v>
        <v>NewState = term()</v>
        <v>Code = undef | enoent | eacces | enospc</v>
        <v>&nbsp;&nbsp;| badop | eexist | baduser | badopt</v>
        <v>&nbsp;&nbsp;| int()</v>
        <v>Text = string()</v>
      </type>
      <desc>
        <p>Opens a file for read or write access.</p>
        <p>On the client side where the <c>open/5</c> call has been
	preceded by a call to <c>prepare/5</c>, all options must be
	accepted or rejected.</p>
	<p>On the server side, where there is no preceding
	<c>prepare/5</c> call, no new options may be added, but
	the ones that are present in <c>SuggestedOptions</c> may be
	omitted or replaced with new values in <c>AcceptedOptions</c>.</p>
    
	<marker id="read"></marker>
      </desc>
    </func>

    <func>
      <name>read(State) -> {more, Bin, NewState} | {last, Bin, FileSize} | {error, {Code, Text}}</name>
      <fsummary>Read a chunk from the file</fsummary>
      <type>
        <v>State = NewState = term()</v>
        <v>Bin = binary()</v>
        <v>FileSize = int()</v>
        <v>Code = undef | enoent | eacces | enospc</v>
        <v>&nbsp;&nbsp;| badop | eexist | baduser | badopt</v>
        <v>&nbsp;&nbsp;| int()</v>
        <v>Text = string()</v>
      </type>
      <desc>
        <p>Read a chunk from the file.</p>
        <p>The callback function is expected to close
	the file when the last file chunk is
	encountered. When an error is encountered
	the callback function is expected to clean
	up after the aborted file transfer, such as
	closing open file descriptors etc. In both
	cases there will be no more calls to any of
	the callback functions.</p>
    
	<marker id="write"></marker>
      </desc>
    </func>

    <func>
      <name>write(Bin, State) -> {more, NewState} | {last, FileSize} | {error, {Code, Text}}</name>
      <fsummary>Write a chunk to the file</fsummary>
      <type>
        <v>Bin = binary()</v>
        <v>State = NewState = term()</v>
        <v>FileSize = int()</v>
        <v>Code = undef | enoent | eacces | enospc</v>
        <v>&nbsp;&nbsp;| badop | eexist | baduser | badopt</v>
        <v>&nbsp;&nbsp;| int()</v>
        <v>Text = string()</v>
      </type>
      <desc>
        <p>Write a chunk to the file.</p>
        <p>The callback function is expected to close
	the file when the last file chunk is
	encountered. When an error is encountered
	the callback function is expected to clean
	up after the aborted file transfer, such as
	closing open file descriptors etc. In both
	cases there will be no more calls to any of
	the callback functions.</p>
    
	<marker id="abort"></marker>
      </desc>
    </func>

    <func>
      <name>abort(Code, Text, State) -> ok</name>
      <fsummary>Abort the file transfer</fsummary>
      <type>
        <v>Code = undef | enoent | eacces | enospc</v>
        <v>&nbsp;&nbsp;| badop | eexist | baduser | badopt</v>
        <v>&nbsp;&nbsp;| int()</v>
        <v>Text = string()</v>
        <v>State = term()</v>
      </type>
      <desc>
        <p>Invoked when the file transfer is aborted.</p>
        <p>The callback function is expected to clean
	up its used resources after the aborted file
	transfer, such as closing open file
	descriptors etc. The function will not be
	invoked if any of the other callback
	functions returns an error, as it is
	expected that they already have cleaned up
	the necessary resources. It will however be
	invoked if the functions fails (crashes).</p>
      </desc>
    </func>
  </funcs>
  
  <section>
    <marker id="tftp_logger"></marker>
    <title>LOGGER FUNCTIONS</title>
    
    <p>A <c>tftp_logger</c> callback module should be implemented as a
    <c>tftp_logger</c> behavior and export the functions listed below.</p>
    
    <marker id="error_msg"></marker>
    </section>

  <funcs>
    <func>
      <name>error_msg(Format, Data) -> ok | exit(Reason)</name>
      <fsummary>Log an error message</fsummary>
      <type>
        <v>Format = string()</v>
        <v>Data = [term()]</v>
        <v>Reason = term()</v>
      </type>
      <desc>
	<p>Log an error message. 
	See <c>error_logger:error_msg/2 for details.</c> </p>
	
	<marker id="warning_msg"></marker>
      </desc>
    </func>

    <func>
      <name>warning_msg(Format, Data) -> ok | exit(Reason)</name>
      <fsummary>Log an error message</fsummary>
      <type>
        <v>Format = string()</v>
        <v>Data = [term()]</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Log a warning message. 
	See <c>error_logger:warning_msg/2 for details.</c> </p>
	
	<marker id="info_msg"></marker>
      </desc>
    </func>

    <func>
      <name>info_msg(Format, Data) -> ok | exit(Reason)</name>
      <fsummary>Log an error message</fsummary>
      <type>
        <v>Format = string()</v>
        <v>Data = [term()]</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Log an info message. 
	See <c>error_logger:info_msg/2 for details.</c> </p>
      </desc>
    </func>
  </funcs>
</erlref>