[RFC PATCH 2/5] samples/damon/wsse: implement DAMON starting and stopping

[SeongJae Park <sj@kernel.org>]

Start running DAMON for the process that user requested to estimate the
process via 'pid' parameter, when 'y' is passed to 'enable' parameter.
If 'n' is passed, stop running DAMON.  Iterating the DAMON monitoring
results and estimating the working set side is not yet implemented.  It
will be implemented by the following commit.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 samples/damon/wsse.c | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/samples/damon/wsse.c b/samples/damon/wsse.c
index 5912f15181c8..119ac8a2c901 100644
--- a/samples/damon/wsse.c
+++ b/samples/damon/wsse.c
@@ -27,15 +27,48 @@ static bool enable __read_mostly;
 module_param_cb(enable, &enable_param_ops, &enable, 0600);
 MODULE_PARM_DESC(enable, "Enable or disable DAMON_SAMPLE_WSSE");
 
+static struct damon_ctx *ctx;
+static struct pid *target_pidp;
+
 static int damon_sample_wsse_start(void)
 {
+	struct damon_target *target;
+
 	pr_info("start\n");
-	return 0;
+
+	ctx = damon_new_ctx();
+	if (!ctx)
+		return -ENOMEM;
+	if (damon_select_ops(ctx, DAMON_OPS_VADDR)) {
+		damon_destroy_ctx(ctx);
+		return -EINVAL;
+	}
+
+	target = damon_new_target();
+	if (!target) {
+		damon_destroy_ctx(ctx);
+		return -ENOMEM;
+	}
+	damon_add_target(ctx, target);
+	target_pidp = find_get_pid(target_pid);
+	if (!target_pidp) {
+		damon_destroy_ctx(ctx);
+		return -EINVAL;
+	}
+	target->pid = target_pidp;
+
+	return damon_start(&ctx, 1, true);
 }
 
 static void damon_sample_wsse_stop(void)
 {
 	pr_info("stop\n");
+	if (ctx) {
+		damon_stop(&ctx, 1);
+		damon_destroy_ctx(ctx);
+	}
+	if (target_pidp)
+		put_pid(target_pidp);
 }
 
 static int damon_sample_wsse_enable_store(
-- 
2.39.5