media/v4l/func-read.xml

1 <refentry id="func-read">
3     <refentrytitle>V4L2 read()</refentrytitle>
8     <refname>v4l2-read</refname>
9     <refpurpose>Read from a V4L2 device</refpurpose>
16 	<funcdef>ssize_t <function>read</function></funcdef>
52     <para><function>read()</function> attempts to read up to
57 <function>read()</function> returns zero and has no other results. If
61 <function>read()</function> call will provide at most one frame (two
64     <para>By default <function>read()</function> blocks until data
70 drivers supporting the <function>read()</function> function must also
74     <para>Drivers can implement read functionality in different
78     <para><function>read()</function> never returns a "snapshot" of a
81 read is finished. Thus only the period of the vertical blanking
86 <function>read()</function> when called during the active picture
90 overwriting the previously, not read frame, and returns the frame
91 being received at the time of the <function>read()</function> call as
95 the next <function>read()</function> call. The frame being received at
96 <function>read()</function> time is discarded, returning the following
99 is the video read mode of the bttv driver, initiating a DMA to user
100 memory when <function>read()</function> is called and returning when
119     <para>On success, the number of bytes read is returned. It is not
122 example because <function>read()</function> was interrupted by a
124 variable is set appropriately. In this case the next read will start
146 	  <para>The driver does not support multiple read streams and the
161 data was read.</para>
174 	  <para>The <function>read()</function> function is not