From: Mathieu Desnoyers Date: Wed, 18 May 2016 14:06:45 +0000 (-0400) Subject: Documentation: ring buffer: SWITCH_FLUSH can be used when active X-Git-Tag: v2.6.7~2 X-Git-Url: http://git.liburcu.org/?p=lttng-ust.git;a=commitdiff_plain;h=5c67b05c1736b91a1b8b9799e54855e1e1f57f16 Documentation: ring buffer: SWITCH_FLUSH can be used when active Snapshot mode tracing may use SWITCH_FLUSH while tracing is active. Signed-off-by: Mathieu Desnoyers --- diff --git a/libringbuffer/ring_buffer_frontend.c b/libringbuffer/ring_buffer_frontend.c index 6c3fa740..7136abbc 100644 --- a/libringbuffer/ring_buffer_frontend.c +++ b/libringbuffer/ring_buffer_frontend.c @@ -1386,7 +1386,8 @@ void lib_ring_buffer_print_errors(struct channel *chan, /* * lib_ring_buffer_switch_old_start: Populate old subbuffer header. * - * Only executed when the buffer is finalized, in SWITCH_FLUSH. + * Only executed by SWITCH_FLUSH, which can be issued while tracing is + * active or at buffer finalization (destroy). */ static void lib_ring_buffer_switch_old_start(struct lttng_ust_lib_ring_buffer *buf, @@ -1560,12 +1561,14 @@ int lib_ring_buffer_try_switch_slow(enum switch_mode mode, unsigned long sb_index, commit_count; /* - * We are performing a SWITCH_FLUSH. At this stage, there are no - * concurrent writes into the buffer. + * We are performing a SWITCH_FLUSH. There may be concurrent + * writes into the buffer if e.g. invoked while performing a + * snapshot on an active trace. * - * The client does not save any header information. Don't - * switch empty subbuffer on finalize, because it is invalid to - * deliver a completely empty subbuffer. + * If the client does not save any header information + * (sub-buffer header size == 0), don't switch empty subbuffer + * on finalize, because it is invalid to deliver a completely + * empty subbuffer. */ if (!config->cb.subbuffer_header_size()) return -1;