diff options
Diffstat (limited to 'Documentation/DocBook/media/v4l/func-poll.xml')
| -rw-r--r-- | Documentation/DocBook/media/v4l/func-poll.xml | 142 |
1 files changed, 0 insertions, 142 deletions
diff --git a/Documentation/DocBook/media/v4l/func-poll.xml b/Documentation/DocBook/media/v4l/func-poll.xml deleted file mode 100644 index 4c73f115219b..000000000000 --- a/Documentation/DocBook/media/v4l/func-poll.xml +++ /dev/null @@ -1,142 +0,0 @@ -<refentry id="func-poll"> - <refmeta> - <refentrytitle>V4L2 poll()</refentrytitle> - &manvol; - </refmeta> - - <refnamediv> - <refname>v4l2-poll</refname> - <refpurpose>Wait for some event on a file descriptor</refpurpose> - </refnamediv> - - <refsynopsisdiv> - <funcsynopsis> - <funcsynopsisinfo>#include <sys/poll.h></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>With the <function>poll()</function> function applications -can suspend execution until the driver has captured data or is ready -to accept data for output.</para> - - <para>When streaming I/O has been negotiated this function waits -until a buffer has been filled by the capture device and can be dequeued -with the &VIDIOC-DQBUF; ioctl. For output devices this function waits -until the device is ready to accept a new buffer to be queued up with -the &VIDIOC-QBUF; ioctl for display. When buffers are already in the outgoing -queue of the driver (capture) or the incoming queue isn't full (display) -the function returns immediately.</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). -Capture devices set the <constant>POLLIN</constant> and -<constant>POLLRDNORM</constant> flags in the -<structfield>revents</structfield> field, output devices the -<constant>POLLOUT</constant> and <constant>POLLWRNORM</constant> -flags. 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. When the -application did not call &VIDIOC-STREAMON; the -<function>poll()</function> function succeeds, but sets the -<constant>POLLERR</constant> flag in the -<structfield>revents</structfield> field. When the -application has called &VIDIOC-STREAMON; for a capture device but hasn't -yet called &VIDIOC-QBUF;, the <function>poll()</function> function -succeeds and sets the <constant>POLLERR</constant> flag in the -<structfield>revents</structfield> field. For output devices this -same situation will cause <function>poll()</function> to succeed -as well, but it sets the <constant>POLLOUT</constant> and -<constant>POLLWRNORM</constant> flags in the <structfield>revents</structfield> -field.</para> - - <para>If an event occurred (see &VIDIOC-DQEVENT;) then -<constant>POLLPRI</constant> will be set in the <structfield>revents</structfield> -field and <function>poll()</function> will return.</para> - - <para>When use of the <function>read()</function> function has -been negotiated and the driver does not capture yet, the -<function>poll</function> function starts capturing. When that fails -it returns a <constant>POLLERR</constant> as above. Otherwise it waits -until data has been captured and can be read. When the driver captures -continuously (as opposed to, for example, still images) the function -may return immediately.</para> - - <para>When use of the <function>write()</function> function has -been negotiated and the driver does not stream yet, the -<function>poll</function> function starts streaming. When that fails -it returns a <constant>POLLERR</constant> as above. Otherwise it waits -until the driver is ready for a non-blocking -<function>write()</function> call.</para> - - <para>If the caller is only interested in events (just -<constant>POLLPRI</constant> is set in the <structfield>events</structfield> -field), then <function>poll()</function> will <emphasis>not</emphasis> -start streaming if the driver does not stream yet. This makes it -possible to just poll for events and not for buffers.</para> - - <para>All drivers implementing the <function>read()</function> or -<function>write()</function> function or streaming I/O must also -support the <function>poll()</function> function.</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>EBUSY</errorcode></term> - <listitem> - <para>The driver does not support multiple read or write -streams and the device is already in use.</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> |