1<refentry id="func-open"> 2 <refmeta> 3 <refentrytitle>V4L2 open()</refentrytitle> 4 &manvol; 5 </refmeta> 6 7 <refnamediv> 8 <refname>v4l2-open</refname> 9 <refpurpose>Open a V4L2 device</refpurpose> 10 </refnamediv> 11 12 <refsynopsisdiv> 13 <funcsynopsis> 14 <funcsynopsisinfo>#include <fcntl.h></funcsynopsisinfo> 15 <funcprototype> 16 <funcdef>int <function>open</function></funcdef> 17 <paramdef>const char *<parameter>device_name</parameter></paramdef> 18 <paramdef>int <parameter>flags</parameter></paramdef> 19 </funcprototype> 20 </funcsynopsis> 21 </refsynopsisdiv> 22 23 <refsect1> 24 <title>Arguments</title> 25 26 <variablelist> 27 <varlistentry> 28 <term><parameter>device_name</parameter></term> 29 <listitem> 30 <para>Device to be opened.</para> 31 </listitem> 32 </varlistentry> 33 <varlistentry> 34 <term><parameter>flags</parameter></term> 35 <listitem> 36 <para>Open flags. Access mode must be 37<constant>O_RDWR</constant>. This is just a technicality, input devices 38still support only reading and output devices only writing.</para> 39 <para>When the <constant>O_NONBLOCK</constant> flag is 40given, the read() function and the &VIDIOC-DQBUF; ioctl will return 41the &EAGAIN; when no data is available or no buffer is in the driver 42outgoing queue, otherwise these functions block until data becomes 43available. All V4L2 drivers exchanging data with applications must 44support the <constant>O_NONBLOCK</constant> flag.</para> 45 <para>Other flags have no effect.</para> 46 </listitem> 47 </varlistentry> 48 </variablelist> 49 </refsect1> 50 <refsect1> 51 <title>Description</title> 52 53 <para>To open a V4L2 device applications call 54<function>open()</function> with the desired device name. This 55function has no side effects; all data format parameters, current 56input or output, control values or other properties remain unchanged. 57At the first <function>open()</function> call after loading the driver 58they will be reset to default values, drivers are never in an 59undefined state.</para> 60 </refsect1> 61 <refsect1> 62 <title>Return Value</title> 63 64 <para>On success <function>open</function> returns the new file 65descriptor. On error -1 is returned, and the <varname>errno</varname> 66variable is set appropriately. Possible error codes are:</para> 67 68 <variablelist> 69 <varlistentry> 70 <term><errorcode>EACCES</errorcode></term> 71 <listitem> 72 <para>The caller has no permission to access the 73device.</para> 74 </listitem> 75 </varlistentry> 76 <varlistentry> 77 <term><errorcode>EBUSY</errorcode></term> 78 <listitem> 79 <para>The driver does not support multiple opens and the 80device is already in use.</para> 81 </listitem> 82 </varlistentry> 83 <varlistentry> 84 <term><errorcode>ENXIO</errorcode></term> 85 <listitem> 86 <para>No device corresponding to this device special file 87exists.</para> 88 </listitem> 89 </varlistentry> 90 <varlistentry> 91 <term><errorcode>ENOMEM</errorcode></term> 92 <listitem> 93 <para>Not enough kernel memory was available to complete the 94request.</para> 95 </listitem> 96 </varlistentry> 97 <varlistentry> 98 <term><errorcode>EMFILE</errorcode></term> 99 <listitem> 100 <para>The process already has the maximum number of 101files open.</para> 102 </listitem> 103 </varlistentry> 104 <varlistentry> 105 <term><errorcode>ENFILE</errorcode></term> 106 <listitem> 107 <para>The limit on the total number of files open on the 108system has been reached.</para> 109 </listitem> 110 </varlistentry> 111 </variablelist> 112 </refsect1> 113</refentry> 114 115<!-- 116Local Variables: 117mode: sgml 118sgml-parent-document: "v4l2.sgml" 119indent-tabs-mode: nil 120End: 121--> 122