Fix: use "flush empty" ioctl for snapshots
authorMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Thu, 11 May 2017 21:53:58 +0000 (17:53 -0400)
committerJérémie Galarneau <jeremie.galarneau@efficios.com>
Fri, 19 May 2017 21:00:51 +0000 (17:00 -0400)
commitf22dd89135f6b1749cd75735f04e3cb309da12c1
tree1db7c41e97eb7ff2b7d5926e59590eb5aaa8eb8c
parent001b7e62c1cb15f9d6cb835647b81028d56cf2d8
Fix: use "flush empty" ioctl for snapshots

When the flush empty ioctl is available, use it to produce an empty
packet at the end of the snapshot, which ensures the stream intersection
feature works.

If this specific ioctl is not available, fallback on the "flush" ioctl,
which does not produce empty packets.

In that situation, there were two prior behaviors possible for
lttng-modules: earlier versions implement a "snapshot" command which
does not perform an implicit "flush_empty". In that case, the stream
intersection feature may not be reliable. In more recent lttng-modules
versions (included stable branch) which did not implement the
flush_empty ioctl, the snapshot ioctl implicitly performed a
flush_empty, which makes the stream intersection feature work, but has
side-effects on the snapshot ioctl performed by the live timer (produces
a stream of empty packets in live mode).

[ Please apply to master, 2.10, 2.9, 2.8 branches. ]

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
src/common/kernel-consumer/kernel-consumer.c
src/common/kernel-ctl/kernel-ctl.c
src/common/kernel-ctl/kernel-ctl.h
src/common/kernel-ctl/kernel-ioctl.h
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