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