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[media] DocBook media: fix the poll() 'no QBUF' documentation

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Clarify what poll() returns if STREAMON was called but not QBUF.
Make explicit the different behavior for this scenario for
capture and output devices.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
This commit is contained in:
Hans Verkuil 2014-09-20 16:16:36 -03:00 committed by Mauro Carvalho Chehab
parent 58d75f4b1c
commit acf92046a0
1 changed files with 10 additions and 2 deletions
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12
Documentation/DocBook/media/v4l/func-poll.xml
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@ -44,10 +44,18 @@ Capture devices set the <constant>POLLIN</constant> and
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
application did not call &VIDIOC-STREAMON; the
<function>poll()</function> function succeeds, but sets the
<constant>POLLERR</constant> flag in the
<structfield>revents</structfield> field.</para>
<structfield>revents</structfield> field. When the
application has called &VIDIOC-STREAMON; for a capture device but hasn't
yet called &VIDIOC-QBUF;, the <function>poll()</function> function
succeeds and sets the <constant>POLLERR</constant> flag in the
<structfield>revents</structfield> field. For output devices this
same situation will cause <function>poll()</function> to succeed
as well, but it sets the <constant>POLLOUT</constant> and
<constant>POLLWRNORM</constant> flags 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