[Bug 765801] New: v4l2: pipeline crashes when GST_DEBUG_DUMP_DOT_DIR is enabled

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=765801

            Bug ID: 765801
           Summary: v4l2: pipeline crashes when GST_DEBUG_DUMP_DOT_DIR is
                    enabled
    Classification: Platform
           Product: GStreamer
           Version: git master
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gst-plugins-good
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: arjen.veenhuizen at tno.nl
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

Platform: Ubuntu 14.04 x64
GStreamer: master, but has been observed on other releases as well (e.g. 1.6.x)

When dot file generation is enabled (with the required dependencies and setting
GST_DEBUG_DUMP_DOT_DIR), pipelines using v4l2src and v4l2sink crash.


For example, this pipeline works when your webcam is connected to /dev/video0:

export GST_DEBUG_DUMP_DOT_DIR=; gst-launch-1.0 v4l2src device=/dev/video0 !
autovideosink

However, this pipeline does not work and causes errors/segfaults:

export GST_DEBUG_DUMP_DOT_DIR=/tmp/; gst-launch-1.0 v4l2src device=/dev/video0
! autovideosink

This problem was already reported back in 2013 for gstreamer-0.10 [1] but still
seems to be around. Stefan Sauer assessment read back then:

By default the dot dump include element properties that are different 
from the defaults. I sounds to me that reading the properties on your 
life v4l2src trips it up. I wonder if some variables are marked as readable,
but in fact are not. 

[1]
http://gstreamer-devel.966125.n4.nabble.com/problem-with-GST-DEBUG-DUMP-DOT-DIR-amp-v4l2src-td4656432.html

Small excerpt from stdout: 

WARNING: from element /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: Failed to get
value for control 9963779 on device '/dev/video0'.
Additional debug info:
v4l2_calls.c(928): gst_v4l2_get_attribute ():
/GstPipeline:pipeline0/GstV4l2Src:v4l2src0:
system error: Invalid argument
WARNING: from element /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: Failed to get
value for control 9963779 on device '/dev/video0'.
Additional debug info:
v4l2_calls.c(928): gst_v4l2_get_attribute ():
/GstPipeline:pipeline0/GstV4l2Src:v4l2src0:
system error: Invalid argument
WARNING: from element /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: Failed to get
value for control 9963779 on device '/dev/video0'.
Additional debug info:
v4l2_calls.c(928): gst_v4l2_get_attribute ():
/GstPipeline:pipeline0/GstV4l2Src:v4l2src0:
system error: Invalid argument

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