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-<refentry id="func-write">
- <refmeta>
- <refentrytitle>V4L2 write()</refentrytitle>
- &manvol;
- </refmeta>
-
- <refnamediv>
- <refname>v4l2-write</refname>
- <refpurpose>Write to a V4L2 device</refpurpose>
- </refnamediv>
-
- <refsynopsisdiv>
- <funcsynopsis>
- <funcsynopsisinfo>#include &lt;unistd.h&gt;</funcsynopsisinfo>
- <funcprototype>
- <funcdef>ssize_t <function>write</function></funcdef>
- <paramdef>int <parameter>fd</parameter></paramdef>
- <paramdef>void *<parameter>buf</parameter></paramdef>
- <paramdef>size_t <parameter>count</parameter></paramdef>
- </funcprototype>
- </funcsynopsis>
- </refsynopsisdiv>
-
- <refsect1>
- <title>Arguments</title>
-
- <variablelist>
- <varlistentry>
- <term><parameter>fd</parameter></term>
- <listitem>
- <para>&fd;</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><parameter>buf</parameter></term>
- <listitem>
- <para></para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><parameter>count</parameter></term>
- <listitem>
- <para></para>
- </listitem>
- </varlistentry>
- </variablelist>
- </refsect1>
-
- <refsect1>
- <title>Description</title>
-
- <para><function>write()</function> writes up to
-<parameter>count</parameter> bytes to the device referenced by the
-file descriptor <parameter>fd</parameter> from the buffer starting at
-<parameter>buf</parameter>. When the hardware outputs are not active
-yet, this function enables them. When <parameter>count</parameter> is
-zero, <function>write()</function> returns
-<returnvalue>0</returnvalue> without any other effect.</para>
-
- <para>When the application does not provide more data in time, the
-previous video frame, raw VBI image, sliced VPS or WSS data is
-displayed again. Sliced Teletext or Closed Caption data is not
-repeated, the driver inserts a blank line instead.</para>
- </refsect1>
-
- <refsect1>
- <title>Return Value</title>
-
- <para>On success, the number of bytes written are returned. Zero
-indicates nothing was written. On error, <returnvalue>-1</returnvalue>
-is returned, and the <varname>errno</varname> variable is set
-appropriately. In this case the next write will start at the beginning
-of a new frame. Possible error codes are:</para>
-
- <variablelist>
- <varlistentry>
- <term><errorcode>EAGAIN</errorcode></term>
- <listitem>
- <para>Non-blocking I/O has been selected using the <link
-linkend="func-open"><constant>O_NONBLOCK</constant></link> flag and no
-buffer space was available to write the data immediately.</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><errorcode>EBADF</errorcode></term>
- <listitem>
- <para><parameter>fd</parameter> is not a valid file
-descriptor or is not open for writing.</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><errorcode>EBUSY</errorcode></term>
- <listitem>
- <para>The driver does not support multiple write streams and the
-device is already in use.</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><errorcode>EFAULT</errorcode></term>
- <listitem>
- <para><parameter>buf</parameter> references an inaccessible
-memory area.</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><errorcode>EINTR</errorcode></term>
- <listitem>
- <para>The call was interrupted by a signal before any
-data was written.</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><errorcode>EIO</errorcode></term>
- <listitem>
- <para>I/O error. This indicates some hardware problem.</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><errorcode>EINVAL</errorcode></term>
- <listitem>
- <para>The <function>write()</function> function is not
-supported by this driver, not on this device, or generally not on this
-type of device.</para>
- </listitem>
- </varlistentry>
- </variablelist>
- </refsect1>
-</refentry>