122 lines
3.5 KiB
XML
122 lines
3.5 KiB
XML
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<refentry id="func-open">
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<refmeta>
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<refentrytitle>V4L2 open()</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>v4l2-open</refname>
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<refpurpose>Open 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 <fcntl.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>open</function></funcdef>
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<paramdef>const char *<parameter>device_name</parameter></paramdef>
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<paramdef>int <parameter>flags</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>device_name</parameter></term>
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<listitem>
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<para>Device to be opened.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>flags</parameter></term>
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<listitem>
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<para>Open flags. Access mode must be
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<constant>O_RDWR</constant>. This is just a technicality, input devices
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still support only reading and output devices only writing.</para>
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<para>When the <constant>O_NONBLOCK</constant> flag is
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given, the read() function and the &VIDIOC-DQBUF; ioctl will return
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the &EAGAIN; when no data is available or no buffer is in the driver
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outgoing queue, otherwise these functions block until data becomes
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available. All V4L2 drivers exchanging data with applications must
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support the <constant>O_NONBLOCK</constant> flag.</para>
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<para>Other flags have no effect.</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 open a V4L2 device applications call
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<function>open()</function> with the desired device name. This
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function has no side effects; all data format parameters, current
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input or output, control values or other properties remain unchanged.
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At the first <function>open()</function> call after loading the driver
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they will be reset to default values, drivers are never in an
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undefined state.</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 <function>open</function> returns the new file
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descriptor. On error -1 is returned, and the <varname>errno</varname>
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variable is set appropriately. Possible error codes are:</para>
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<variablelist>
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<varlistentry>
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<term><errorcode>EACCES</errorcode></term>
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<listitem>
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<para>The caller has no permission to access the
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device.</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 opens 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>ENXIO</errorcode></term>
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<listitem>
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<para>No device corresponding to this device special file
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exists.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>ENOMEM</errorcode></term>
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<listitem>
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<para>Not enough kernel memory was available to complete the
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request.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>EMFILE</errorcode></term>
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<listitem>
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<para>The process already has the maximum number of
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files open.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>ENFILE</errorcode></term>
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<listitem>
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<para>The limit on the total number of files open on the
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system has been reached.</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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