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author | Linus Torvalds <torvalds@linux-foundation.org> | 2009-09-21 09:03:10 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-09-21 09:03:10 -0700 |
commit | c720f5655df159a630fa0290a0bd67c93e92b0bf (patch) | |
tree | 940d139d0ec1ff5201efddef6cc663166a8a2df3 /Documentation/DocBook/v4l/func-poll.xml | |
parent | Merge branch 'linux-next' of git://git.infradead.org/ubifs-2.6 (diff) | |
parent | V4L/DVB (13033): pt1: Don't use a deprecated DMA_BIT_MASK macro (diff) | |
download | linux-dev-c720f5655df159a630fa0290a0bd67c93e92b0bf.tar.xz linux-dev-c720f5655df159a630fa0290a0bd67c93e92b0bf.zip |
Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-2.6
* 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-2.6: (222 commits)
V4L/DVB (13033): pt1: Don't use a deprecated DMA_BIT_MASK macro
V4L/DVB (13029): radio-si4713: remove #include <linux/version.h>
V4L/DVB (13027): go7007: convert printks to v4l2_info
V4L/DVB (13026): s2250-board: Implement brightness and contrast controls
V4L/DVB (13025): s2250-board: Fix memory leaks
V4L/DVB (13024): go7007: Implement vidioc_g_std and vidioc_querystd
V4L/DVB (13023): go7007: Merge struct gofh and go declarations
V4L/DVB (13022): go7007: Fix mpeg controls
V4L/DVB (13021): go7007: Fix whitespace and line lengths
V4L/DVB (13020): go7007: Updates to Kconfig and Makefile
V4L/DVB (13019): video: initial support for ADV7180
V4L/DVB (13018): kzalloc failure ignored in au8522_probe()
V4L/DVB (13017): gspca: kmalloc failure ignored in sd_start()
V4L/DVB (13016): kmalloc failure ignored in lgdt3304_attach() and s921_attach()
V4L/DVB (13015): kmalloc failure ignored in m920x_firmware_download()
V4L/DVB (13014): Add support for Compro VideoMate E800 (DVB-T part only)
V4L/DVB (13013): FM TX: si4713: Kconfig: Fixed two typos.
V4L/DVB (13012): uvc: introduce missing kfree
V4L/DVB (13011): Change tuner type of BeholdTV cards
V4L/DVB (13009): gspca - stv06xx-hdcs: Reduce exposure range
...
Diffstat (limited to 'Documentation/DocBook/v4l/func-poll.xml')
-rw-r--r-- | Documentation/DocBook/v4l/func-poll.xml | 127 |
1 files changed, 127 insertions, 0 deletions
diff --git a/Documentation/DocBook/v4l/func-poll.xml b/Documentation/DocBook/v4l/func-poll.xml new file mode 100644 index 000000000000..ec3c718f5963 --- /dev/null +++ b/Documentation/DocBook/v4l/func-poll.xml @@ -0,0 +1,127 @@ +<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 <sys/poll.h></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: +--> |