diff options
Diffstat (limited to 'Documentation/DocBook/v4l/func-write.xml')
| -rw-r--r-- | Documentation/DocBook/v4l/func-write.xml | 136 |
1 files changed, 136 insertions, 0 deletions
diff --git a/Documentation/DocBook/v4l/func-write.xml b/Documentation/DocBook/v4l/func-write.xml new file mode 100644 index 00000000000..2c09c09371c --- /dev/null +++ b/Documentation/DocBook/v4l/func-write.xml @@ -0,0 +1,136 @@ +<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 <unistd.h></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> + +<!-- +Local Variables: +mode: sgml +sgml-parent-document: "v4l2.sgml" +indent-tabs-mode: nil +End: +--> |