[OSSTEST PATCH v2 05/41] sg-report-flight: Add a comment re same-flight search narrowing

[Ian Jackson <ian.jackson@eu.citrix.com>]

In afe851ca1771e5da6395b596afa69e509dbbc278
  sg-report-flight: When justifying, disregard out-of-flight build jobs
we narrowed sg-report-flight's search algorith.

An extensive justification is in the commit message.  I think much of
this information belongs in-tree, so c&p it (with slight edits) here.

No code change.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
---
 sg-report-flight | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/sg-report-flight b/sg-report-flight
index 831917a9..fc439495 100755
--- a/sg-report-flight
+++ b/sg-report-flight
@@ -242,9 +242,27 @@ END
 	# jobs.  We start with all jobs in $tflight, and for each job
 	# we also process any other jobs it refers to in *buildjob runvars.
 	#
+	# The real thing we want to check that the build jobs *in the
+	# same flight as the justifying job* used the right revisions.
+	# Build jobs from other flights were either (i) build jobs for
+	# components not being targed for testing by this branch, but
+	# which were necessary for the justifying job and for which we
+	# decided to reuse another build job (in which case we don't
+	# really care what versions they used, even if underlying it
+	# all there might be a different version of a tree we are
+	# actually interested in (ii) the kind of continuous update
+	# thing seen with freebsdbuildjob.
+	#
+	# (This is rather different to cs-bisection-step, which is
+	# less focused on changes in a particular set of trees.)
+	#
+	# So we limit the scope of our recursive descent into build
+	# jobs, to jobs in the same flight.
+	#
 	# We don't actually use a recursive algorithm because that
 	# would involve recursive use of the same sql query object;
 	# hence the @binfos_todo queue.
+
 	my @binfos_todo;
 	my $binfos_queue = sub {
 	    my ($inflight,$q,$why) = @_;
-- 
2.20.1