Allow runsc to generate coverage reports.

Add a coverage-report flag that will cause the sandbox to generate a coverage
report (with suffix .cov) in the debug log directory upon exiting. For the
report to be generated, runsc must have been built with the following Bazel
flags: `--collect_code_coverage --instrumentation_filter=...`.

With coverage reports, we should be able to aggregate results across all tests
to surface code coverage statistics for the project as a whole.

The report is simply a text file with each line representing a covered block
as `file:start_line.start_col,end_line.end_col`. Note that this is similar to
the format of coverage reports generated with `go test -coverprofile`,
although we omit the count and number of statements, which are not useful for
us.

Some simple ways of getting coverage reports:

bazel test <some_test> --collect_code_coverage \
  --instrumentation_filter=//pkg/...

bazel build //runsc --collect_code_coverage \
  --instrumentation_filter=//pkg/...
runsc -coverage-report=dir/ <other_flags> do ...

PiperOrigin-RevId: 368952911

2 files changed, 5 insertions, 1 deletions

diff --git a/runsc/config/config.go b/runsc/config/config.go
index 0b2b97cc5..fa550ebf7 100644
--- a/runsc/config/config.go
+++ b/runsc/config/config.go
@@ -55,6 +55,9 @@ type Config struct {
 	// PanicLog is the path to log GO's runtime messages, if not empty.
 	PanicLog string `flag:"panic-log"`
 
+	// CoverageReport is the path to write Go coverage information, if not empty.
+	CoverageReport string `flag:"coverage-report"`
+
 	// DebugLogFormat is the log format for debug.
 	DebugLogFormat string `flag:"debug-log-format"`
 
diff --git a/runsc/config/flags.go b/runsc/config/flags.go
index 13a1a0163..c3dca2352 100644
--- a/runsc/config/flags.go
+++ b/runsc/config/flags.go
@@ -44,7 +44,8 @@ func RegisterFlags() {
 
 		// Debugging flags.
 		flag.String("debug-log", "", "additional location for logs. If it ends with '/', log files are created inside the directory with default names. The following variables are available: %TIMESTAMP%, %COMMAND%.")
-		flag.String("panic-log", "", "file path were panic reports and other Go's runtime messages are written.")
+		flag.String("panic-log", "", "file path where panic reports and other Go's runtime messages are written.")
+		flag.String("coverage-report", "", "file path where Go coverage reports are written. Reports will only be generated if runsc is built with --collect_code_coverage and --instrumentation_filter Bazel flags.")
 		flag.Bool("log-packets", false, "enable network packet logging.")
 		flag.String("debug-log-format", "text", "log format: text (default), json, or json-k8s.")
 		flag.Bool("alsologtostderr", false, "send log messages to stderr.")