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authorMauro Carvalho Chehab <mchehab@s-opensource.com>2016-07-27 06:32:31 -0300
committerMauro Carvalho Chehab <mchehab@s-opensource.com>2016-07-28 20:08:19 -0300
commit43f71d93a0cb342f0c918fba3f6abb7661e40ad2 (patch)
treea1dc7288bc480e7027ca1827ca4876472fa12e40 /Documentation/DocBook/media/v4l/func-select.xml
parentff9a082fda424257976f08fce942609f358015e0 (diff)
downloadlwn-43f71d93a0cb342f0c918fba3f6abb7661e40ad2.tar.gz
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doc-rst: Remove the media docbook
Now that all media documentation was converted to Sphinx, we should get rid of the old DocBook one, as we don't want people to submit patches against the old stuff. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Acked-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
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-<refentry id="func-select">
- <refmeta>
- <refentrytitle>V4L2 select()</refentrytitle>
- &manvol;
- </refmeta>
-
- <refnamediv>
- <refname>v4l2-select</refname>
- <refpurpose>Synchronous I/O multiplexing</refpurpose>
- </refnamediv>
-
- <refsynopsisdiv>
- <funcsynopsis>
- <funcsynopsisinfo>
-#include &lt;sys/time.h&gt;
-#include &lt;sys/types.h&gt;
-#include &lt;unistd.h&gt;</funcsynopsisinfo>
- <funcprototype>
- <funcdef>int <function>select</function></funcdef>
- <paramdef>int <parameter>nfds</parameter></paramdef>
- <paramdef>fd_set *<parameter>readfds</parameter></paramdef>
- <paramdef>fd_set *<parameter>writefds</parameter></paramdef>
- <paramdef>fd_set *<parameter>exceptfds</parameter></paramdef>
- <paramdef>struct timeval *<parameter>timeout</parameter></paramdef>
- </funcprototype>
- </funcsynopsis>
- </refsynopsisdiv>
-
- <refsect1>
- <title>Description</title>
-
- <para>With the <function>select()</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 or displayed and can be dequeued with
-the &VIDIOC-DQBUF; ioctl. When buffers are already in the outgoing
-queue of the driver the function returns immediately.</para>
-
- <para>On success <function>select()</function> returns the total
-number of bits set in the <structname>fd_set</structname>s. 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-QBUF; or &VIDIOC-STREAMON; yet the
-<function>select()</function> function succeeds, setting the bit of
-the file descriptor in <parameter>readfds</parameter> or
-<parameter>writefds</parameter>, but subsequent &VIDIOC-DQBUF; calls
-will fail.<footnote><para>The Linux kernel implements
-<function>select()</function> like the &func-poll; function, but
-<function>select()</function> cannot return a
-<constant>POLLERR</constant>.</para>
- </footnote></para>
-
- <para>When use of the <function>read()</function> function has
-been negotiated and the driver does not capture yet, the
-<function>select()</function> function starts capturing. When that
-fails, <function>select()</function> returns successful and a
-subsequent <function>read()</function> call, which also attempts to
-start capturing, will return an appropriate error code. When the
-driver captures continuously (as opposed to, for example, still
-images) and data is already available the
-<function>select()</function> function returns immediately.</para>
-
- <para>When use of the <function>write()</function> function has
-been negotiated the <function>select()</function> function just waits
-until the driver is ready for a non-blocking
-<function>write()</function> call.</para>
-
- <para>All drivers implementing the <function>read()</function> or
-<function>write()</function> function or streaming I/O must also
-support the <function>select()</function> function.</para>
-
- <para>For more details see the <function>select()</function>
-manual page.</para>
-
- </refsect1>
-
- <refsect1>
- <title>Return Value</title>
-
- <para>On success, <function>select()</function> returns the number
-of descriptors contained in the three returned descriptor sets, which
-will be zero if the timeout expired. On error
-<returnvalue>-1</returnvalue> is returned, and the
-<varname>errno</varname> variable is set appropriately; the sets and
-<parameter>timeout</parameter> are undefined. Possible error codes
-are:</para>
-
- <variablelist>
- <varlistentry>
- <term><errorcode>EBADF</errorcode></term>
- <listitem>
- <para>One or more of the file descriptor sets specified a
-file descriptor that is not open.</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>The <parameter>readfds</parameter>,
-<parameter>writefds</parameter>, <parameter>exceptfds</parameter> or
-<parameter>timeout</parameter> pointer 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 less than
-zero or greater than <constant>FD_SETSIZE</constant>.</para>
- </listitem>
- </varlistentry>
- </variablelist>
- </refsect1>
-</refentry>