Utilities
v4l2-ctl: Swiss army knife for v4l2.
v4l2-compliance: V4L2 compliance driver testing.
v4l2-dbg: allows access to DBG_G_CHIP_INFO, DBG_G/S_REGISTER.
qv4l2: Qt test application.
Core debugging: 'echo 1 >/sys/class/video4linux/video0/debug'.
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1: show ioctl name
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2: show arguments as well