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authorLinus Torvalds <torvalds@linux-foundation.org>2011-07-30 00:08:53 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-07-30 00:08:53 -0700
commit664a41b8a91bf78a01a751e15175e0008977685a (patch)
treed9dc15c83400ad2dfb430ff27ae3e7fdc9395856 /Documentation/DocBook/media/v4l/func-poll.xml
parent983236b5741e557451f3ed4ec5ebf1f62a5b2c15 (diff)
parentee2ce3a0b43d14d792d34cf88e7bc2091096744b (diff)
Merge branch 'v4l_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-2.6
* 'v4l_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-2.6: (430 commits) [media] ir-mce_kbd-decoder: include module.h for its facilities [media] ov5642: include module.h for its facilities [media] em28xx: Fix DVB-C maxsize for em2884 [media] tda18271c2dd: Fix saw filter configuration for DVB-C @6MHz [media] v4l: mt9v032: Fix Bayer pattern [media] V4L: mt9m111: rewrite set_pixfmt [media] V4L: mt9m111: fix missing return value check mt9m111_reg_clear [media] V4L: initial driver for ov5642 CMOS sensor [media] V4L: sh_mobile_ceu_camera: fix Oops when USERPTR mapping fails [media] V4L: soc-camera: remove soc-camera bus and devices on it [media] V4L: soc-camera: un-export the soc-camera bus [media] V4L: sh_mobile_csi2: switch away from using the soc-camera bus notifier [media] V4L: add media bus configuration subdev operations [media] V4L: soc-camera: group struct field initialisations together [media] V4L: soc-camera: remove now unused soc-camera specific PM hooks [media] V4L: pxa-camera: switch to using standard PM hooks [media] NetUP Dual DVB-T/C CI RF: force card hardware revision by module param [media] Don't OOPS if videobuf_dvb_get_frontend return NULL [media] NetUP Dual DVB-T/C CI RF: load firmware according card revision [media] omap3isp: Support configurable HS/VS polarities ... Fix up conflicts: - arch/arm/mach-omap2/board-rx51-peripherals.c: cleanup regulator supply definitions in mach-omap2 vs OMAP3: RX-51: define vdds_csib regulator supply - drivers/staging/tm6000/tm6000-alsa.c (trivial)
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+<refentry id="func-poll">
+ <refmeta>
+ <refentrytitle>V4L2 poll()</refentrytitle>
+ &manvol;
+ </refmeta>
+
+ <refnamediv>
+ <refname>v4l2-poll</refname>
+ <refpurpose>Wait for some event on a file descriptor</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include &lt;sys/poll.h&gt;</funcsynopsisinfo>
+ <funcprototype>
+ <funcdef>int <function>poll</function></funcdef>
+ <paramdef>struct pollfd *<parameter>ufds</parameter></paramdef>
+ <paramdef>unsigned int <parameter>nfds</parameter></paramdef>
+ <paramdef>int <parameter>timeout</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para>With the <function>poll()</function> function applications
+can suspend execution until the driver has captured data or is ready
+to accept data for output.</para>
+
+ <para>When streaming I/O has been negotiated this function waits
+until a buffer has been filled or displayed and can be dequeued with
+the &VIDIOC-DQBUF; ioctl. When buffers are already in the outgoing
+queue of the driver the function returns immediately.</para>
+
+ <para>On success <function>poll()</function> returns the number of
+file descriptors that have been selected (that is, file descriptors
+for which the <structfield>revents</structfield> field of the
+respective <structname>pollfd</structname> structure is non-zero).
+Capture devices set the <constant>POLLIN</constant> and
+<constant>POLLRDNORM</constant> flags in the
+<structfield>revents</structfield> field, output devices the
+<constant>POLLOUT</constant> and <constant>POLLWRNORM</constant>
+flags. When the function timed out it returns a value of zero, on
+failure it returns <returnvalue>-1</returnvalue> and the
+<varname>errno</varname> variable is set appropriately. When the
+application did not call &VIDIOC-QBUF; or &VIDIOC-STREAMON; yet the
+<function>poll()</function> function succeeds, but sets the
+<constant>POLLERR</constant> flag in the
+<structfield>revents</structfield> field.</para>
+
+ <para>When use of the <function>read()</function> function has
+been negotiated and the driver does not capture yet, the
+<function>poll</function> function starts capturing. When that fails
+it returns a <constant>POLLERR</constant> as above. Otherwise it waits
+until data has been captured and can be read. When the driver captures
+continuously (as opposed to, for example, still images) the function
+may return immediately.</para>
+
+ <para>When use of the <function>write()</function> function has
+been negotiated the <function>poll</function> function just waits
+until the driver is ready for a non-blocking
+<function>write()</function> call.</para>
+
+ <para>All drivers implementing the <function>read()</function> or
+<function>write()</function> function or streaming I/O must also
+support the <function>poll()</function> function.</para>
+
+ <para>For more details see the
+<function>poll()</function> manual page.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Return Value</title>
+
+ <para>On success, <function>poll()</function> returns the number
+structures which have non-zero <structfield>revents</structfield>
+fields, or zero if the call timed out. On error
+<returnvalue>-1</returnvalue> is returned, and the
+<varname>errno</varname> variable is set appropriately:</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><errorcode>EBADF</errorcode></term>
+ <listitem>
+ <para>One or more of the <parameter>ufds</parameter> members
+specify an invalid file descriptor.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><errorcode>EBUSY</errorcode></term>
+ <listitem>
+ <para>The driver does not support multiple read or write
+streams and the device is already in use.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><errorcode>EFAULT</errorcode></term>
+ <listitem>
+ <para><parameter>ufds</parameter> references an inaccessible
+memory area.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><errorcode>EINTR</errorcode></term>
+ <listitem>
+ <para>The call was interrupted by a signal.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><errorcode>EINVAL</errorcode></term>
+ <listitem>
+ <para>The <parameter>nfds</parameter> argument is greater
+than <constant>OPEN_MAX</constant>.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+</refentry>
+
+<!--
+Local Variables:
+mode: sgml
+sgml-parent-document: "v4l2.sgml"
+indent-tabs-mode: nil
+End:
+-->