mirror of https://gitee.com/openkylin/linux.git
129 lines
4.5 KiB
XML
129 lines
4.5 KiB
XML
<refentry id="vidioc-streamon">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_STREAMON</refname>
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<refname>VIDIOC_STREAMOFF</refname>
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<refpurpose>Start or stop streaming I/O</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>const int *<parameter>argp</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>request</parameter></term>
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<listitem>
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<para>VIDIOC_STREAMON, VIDIOC_STREAMOFF</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</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>The <constant>VIDIOC_STREAMON</constant> and
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<constant>VIDIOC_STREAMOFF</constant> ioctl start and stop the capture
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or output process during streaming (<link linkend="mmap">memory
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mapping</link>, <link linkend="userp">user pointer</link> or
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<link linkend="dmabuf">DMABUF</link>) I/O.</para>
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<para>Capture hardware is disabled and no input
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buffers are filled (if there are any empty buffers in the incoming
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queue) until <constant>VIDIOC_STREAMON</constant> has been called.
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Output hardware is disabled and no video signal is
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produced until <constant>VIDIOC_STREAMON</constant> has been called.
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The ioctl will succeed when at least one output buffer is in the
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incoming queue.</para>
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<para>Memory-to-memory devices will not start until
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<constant>VIDIOC_STREAMON</constant> has been called for both the capture
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and output stream types.</para>
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<para>If <constant>VIDIOC_STREAMON</constant> fails then any already
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queued buffers will remain queued.</para>
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<para>The <constant>VIDIOC_STREAMOFF</constant> ioctl, apart of
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aborting or finishing any DMA in progress, unlocks any user pointer
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buffers locked in physical memory, and it removes all buffers from the
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incoming and outgoing queues. That means all images captured but not
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dequeued yet will be lost, likewise all images enqueued for output but
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not transmitted yet. I/O returns to the same state as after calling
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&VIDIOC-REQBUFS; and can be restarted accordingly.</para>
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<para>If buffers have been queued with &VIDIOC-QBUF; and
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<constant>VIDIOC_STREAMOFF</constant> is called without ever having
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called <constant>VIDIOC_STREAMON</constant>, then those queued buffers
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will also be removed from the incoming queue and all are returned to the
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same state as after calling &VIDIOC-REQBUFS; and can be restarted
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accordingly.</para>
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<para>Both ioctls take a pointer to an integer, the desired buffer or
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stream type. This is the same as &v4l2-requestbuffers;
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<structfield>type</structfield>.</para>
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<para>If <constant>VIDIOC_STREAMON</constant> is called when streaming
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is already in progress, or if <constant>VIDIOC_STREAMOFF</constant> is called
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when streaming is already stopped, then 0 is returned. Nothing happens in the
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case of <constant>VIDIOC_STREAMON</constant>, but <constant>VIDIOC_STREAMOFF</constant>
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will return queued buffers to their starting state as mentioned above.</para>
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<para>Note that applications can be preempted for unknown periods right
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before or after the <constant>VIDIOC_STREAMON</constant> or
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<constant>VIDIOC_STREAMOFF</constant> calls, there is no notion of
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starting or stopping "now". Buffer timestamps can be used to
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synchronize with other events.</para>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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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 buffer <structfield>type</structfield> is not supported,
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or no buffers have been allocated (memory mapping) or enqueued
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(output) yet.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>EPIPE</errorcode></term>
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<listitem>
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<para>The driver implements <link
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linkend="pad-level-formats">pad-level format configuration</link> and
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the pipeline configuration is invalid.
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</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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