Based on kernel version 4.7.2. Page generated on 2016-08-22 22:45 EST.
1 <refentry id="func-write"> 2 <refmeta> 3 <refentrytitle>V4L2 write()</refentrytitle> 4 &manvol; 5 </refmeta> 6 7 <refnamediv> 8 <refname>v4l2-write</refname> 9 <refpurpose>Write to a V4L2 device</refpurpose> 10 </refnamediv> 11 12 <refsynopsisdiv> 13 <funcsynopsis> 14 <funcsynopsisinfo>#include <unistd.h></funcsynopsisinfo> 15 <funcprototype> 16 <funcdef>ssize_t <function>write</function></funcdef> 17 <paramdef>int <parameter>fd</parameter></paramdef> 18 <paramdef>void *<parameter>buf</parameter></paramdef> 19 <paramdef>size_t <parameter>count</parameter></paramdef> 20 </funcprototype> 21 </funcsynopsis> 22 </refsynopsisdiv> 23 24 <refsect1> 25 <title>Arguments</title> 26 27 <variablelist> 28 <varlistentry> 29 <term><parameter>fd</parameter></term> 30 <listitem> 31 <para>&fd;</para> 32 </listitem> 33 </varlistentry> 34 <varlistentry> 35 <term><parameter>buf</parameter></term> 36 <listitem> 37 <para></para> 38 </listitem> 39 </varlistentry> 40 <varlistentry> 41 <term><parameter>count</parameter></term> 42 <listitem> 43 <para></para> 44 </listitem> 45 </varlistentry> 46 </variablelist> 47 </refsect1> 48 49 <refsect1> 50 <title>Description</title> 51 52 <para><function>write()</function> writes up to 53 <parameter>count</parameter> bytes to the device referenced by the 54 file descriptor <parameter>fd</parameter> from the buffer starting at 55 <parameter>buf</parameter>. When the hardware outputs are not active 56 yet, this function enables them. When <parameter>count</parameter> is 57 zero, <function>write()</function> returns 58 <returnvalue>0</returnvalue> without any other effect.</para> 59 60 <para>When the application does not provide more data in time, the 61 previous video frame, raw VBI image, sliced VPS or WSS data is 62 displayed again. Sliced Teletext or Closed Caption data is not 63 repeated, the driver inserts a blank line instead.</para> 64 </refsect1> 65 66 <refsect1> 67 <title>Return Value</title> 68 69 <para>On success, the number of bytes written are returned. Zero 70 indicates nothing was written. On error, <returnvalue>-1</returnvalue> 71 is returned, and the <varname>errno</varname> variable is set 72 appropriately. In this case the next write will start at the beginning 73 of a new frame. Possible error codes are:</para> 74 75 <variablelist> 76 <varlistentry> 77 <term><errorcode>EAGAIN</errorcode></term> 78 <listitem> 79 <para>Non-blocking I/O has been selected using the <link 80 linkend="func-open"><constant>O_NONBLOCK</constant></link> flag and no 81 buffer space was available to write the data immediately.</para> 82 </listitem> 83 </varlistentry> 84 <varlistentry> 85 <term><errorcode>EBADF</errorcode></term> 86 <listitem> 87 <para><parameter>fd</parameter> is not a valid file 88 descriptor or is not open for writing.</para> 89 </listitem> 90 </varlistentry> 91 <varlistentry> 92 <term><errorcode>EBUSY</errorcode></term> 93 <listitem> 94 <para>The driver does not support multiple write streams and the 95 device is already in use.</para> 96 </listitem> 97 </varlistentry> 98 <varlistentry> 99 <term><errorcode>EFAULT</errorcode></term> 100 <listitem> 101 <para><parameter>buf</parameter> references an inaccessible 102 memory area.</para> 103 </listitem> 104 </varlistentry> 105 <varlistentry> 106 <term><errorcode>EINTR</errorcode></term> 107 <listitem> 108 <para>The call was interrupted by a signal before any 109 data was written.</para> 110 </listitem> 111 </varlistentry> 112 <varlistentry> 113 <term><errorcode>EIO</errorcode></term> 114 <listitem> 115 <para>I/O error. This indicates some hardware problem.</para> 116 </listitem> 117 </varlistentry> 118 <varlistentry> 119 <term><errorcode>EINVAL</errorcode></term> 120 <listitem> 121 <para>The <function>write()</function> function is not 122 supported by this driver, not on this device, or generally not on this 123 type of device.</para> 124 </listitem> 125 </varlistentry> 126 </variablelist> 127 </refsect1> 128 </refentry>
