projects / deliverable / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| 8e080c2e MCC |
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> |