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145 lines
4.1 KiB
145 lines
4.1 KiB
16 years ago
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<refentry id="vidioc-g-priority">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_G_PRIORITY</refname>
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<refname>VIDIOC_S_PRIORITY</refname>
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<refpurpose>Query or request the access priority associated with a
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file descriptor</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>enum v4l2_priority *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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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 enum v4l2_priority *<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_G_PRIORITY, VIDIOC_S_PRIORITY</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>Pointer to an enum v4l2_priority type.</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>To query the current access priority
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applications call the <constant>VIDIOC_G_PRIORITY</constant> ioctl
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with a pointer to an enum v4l2_priority variable where the driver stores
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the current priority.</para>
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<para>To request an access priority applications store the
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desired priority in an enum v4l2_priority variable and call
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<constant>VIDIOC_S_PRIORITY</constant> ioctl with a pointer to this
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variable.</para>
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<table frame="none" pgwide="1" id="v4l2-priority">
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<title>enum v4l2_priority</title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_PRIORITY_UNSET</constant></entry>
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<entry>0</entry>
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<entry></entry>
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</row>
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<row>
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<entry><constant>V4L2_PRIORITY_BACKGROUND</constant></entry>
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<entry>1</entry>
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<entry>Lowest priority, usually applications running in
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background, for example monitoring VBI transmissions. A proxy
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application running in user space will be necessary if multiple
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applications want to read from a device at this priority.</entry>
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</row>
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<row>
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<entry><constant>V4L2_PRIORITY_INTERACTIVE</constant></entry>
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<entry>2</entry>
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<entry></entry>
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</row>
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<row>
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<entry><constant>V4L2_PRIORITY_DEFAULT</constant></entry>
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<entry>2</entry>
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<entry>Medium priority, usually applications started and
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interactively controlled by the user. For example TV viewers, Teletext
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browsers, or just "panel" applications to change the channel or video
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controls. This is the default priority unless an application requests
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another.</entry>
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</row>
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<row>
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<entry><constant>V4L2_PRIORITY_RECORD</constant></entry>
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<entry>3</entry>
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<entry>Highest priority. Only one file descriptor can have
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this priority, it blocks any other fd from changing device properties.
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Usually applications which must not be interrupted, like video
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recording.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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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 requested priority value is invalid, or the
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driver does not support access priorities.</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>Another application already requested higher
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priority.</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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<!--
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Local Variables:
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mode: sgml
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sgml-parent-document: "v4l2.sgml"
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indent-tabs-mode: nil
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End:
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-->
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