From 09434f96935202d1e6cf64a74d4da4b95d06246d Mon Sep 17 00:00:00 2001 From: Francis Deslauriers Date: Thu, 16 Apr 2020 19:44:06 -0400 Subject: [PATCH] filter: bytecode already in the list should go before Background ========== This `seqnum` (sequence number) feature is currently unused. It was designed so that the session daemon could tell the tracer the order in which the bytecode should be run. Issue ===== The current implementation of the session daemon doesn't use this feature so there is only ever a single bytecode to execute per callsite. During work on an upcoming feature uses this `seqnum` became useful and it was realized that the current bytecode linking code would reverse the order in which the bytecode were executed when all bytecodes have the same `seqnum` value. This is due to the fact that the `cds_list_for_each_entry_reverse` loops until it finds a `seqnum` smaller than the new one. So if all bytecodes have the same `seqnum`, the new bytecode will be added at the beginning of the list. This is not technically a problem since it's the session daemon's job to set the sequence number if it wants a particular ordering. Even considering that, we found it counterintuitive that new bytecodes are added at the beginning of the list in those cases. Solution ======== This commit makes it so that on equality, the insertion is done after the existing bytecodes. Signed-off-by: Francis Deslauriers Signed-off-by: Mathieu Desnoyers Change-Id: Ie323b3ff5df346f222e22abfb9bbad6c5b7e4a27 --- liblttng-ust/lttng-filter.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/liblttng-ust/lttng-filter.c b/liblttng-ust/lttng-filter.c index 1967d540..bbc21289 100644 --- a/liblttng-ust/lttng-filter.c +++ b/liblttng-ust/lttng-filter.c @@ -536,11 +536,12 @@ void lttng_enabler_event_link_bytecode(struct lttng_event *event, /* * Insert at specified priority (seqnum) in increasing - * order. + * order. If there already is a bytecode of the same priority, + * insert the new bytecode right after it. */ cds_list_for_each_entry_reverse(runtime, &event->bytecode_runtime_head, node) { - if (runtime->bc->bc.seqnum < bc->bc.seqnum) { + if (runtime->bc->bc.seqnum <= bc->bc.seqnum) { /* insert here */ insert_loc = &runtime->node; goto add_within; -- 2.34.1