Documentation/DocBook/media/v4l/cec-func-poll.xml

<refentry id="cec-func-poll">
  <refmeta>
    <refentrytitle>cec poll()</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>cec-poll</refname>
    <refpurpose>Wait for some event on a file descriptor</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;sys/poll.h&gt;</funcsynopsisinfo>
      <funcprototype>
	<funcdef>int <function>poll</function></funcdef>
	<paramdef>struct pollfd *<parameter>ufds</parameter></paramdef>
	<paramdef>unsigned int <parameter>nfds</parameter></paramdef>
	<paramdef>int <parameter>timeout</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>
      Note: this documents the proposed CEC API. This API is not yet finalized and
      is currently only available as a staging kernel module.
    </para>

    <para>With the <function>poll()</function> function applications
can wait for CEC events.</para>

    <para>On success <function>poll()</function> returns the number of
file descriptors that have been selected (that is, file descriptors
for which the <structfield>revents</structfield> field of the
respective <structname>pollfd</structname> structure is non-zero).
CEC devices set the <constant>POLLIN</constant> and
<constant>POLLRDNORM</constant> flags in the
<structfield>revents</structfield> field if there are messages in the
receive queue. If the transmit queue has room for new messages, the
<constant>POLLOUT</constant> and <constant>POLLWRNORM</constant>
flags are set. If there are events in the event queue, then the
<constant>POLLPRI</constant> flag is set.
When the function timed out it returns a value of zero, on
failure it returns <returnvalue>-1</returnvalue> and the
<varname>errno</varname> variable is set appropriately.
</para>

    <para>For more details see the
<function>poll()</function> manual page.</para>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para>On success, <function>poll()</function> returns the number
structures which have non-zero <structfield>revents</structfield>
fields, or zero if the call timed out. On error
<returnvalue>-1</returnvalue> is returned, and the
<varname>errno</varname> variable is set appropriately:</para>

    <variablelist>
      <varlistentry>
	<term><errorcode>EBADF</errorcode></term>
	<listitem>
	  <para>One or more of the <parameter>ufds</parameter> members
specify an invalid file descriptor.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><errorcode>EFAULT</errorcode></term>
	<listitem>
	  <para><parameter>ufds</parameter> references an inaccessible
memory area.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><errorcode>EINTR</errorcode></term>
	<listitem>
	  <para>The call was interrupted by a signal.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	  <para>The <parameter>nfds</parameter> argument is greater
than <constant>OPEN_MAX</constant>.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>