[RFC PATCH 3/4] mm/damon/sysfs: Link DAMON to 'state' file read/write functions

[SeongJae Park <sj@kernel.org>]

This commit implements 'state' DAMON sysfs interface file read/write
functions.  In detail, writing 'on' or 'off' to the 'state' file turns
DAMON for the context on or off, accordingly.  Reading the file shows
the state.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 166 +++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 162 insertions(+), 4 deletions(-)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 59bdc7268dc6..721ee086265f 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -793,18 +793,176 @@ static void damon_sysfs_kdamond_rm_dirs(struct damon_sysfs_kdamond *kdamond)
 	kobject_put(&kdamond->contexts->kobj);
 }
 
+static bool damon_sysfs_ctx_running(struct damon_ctx *ctx)
+{
+	bool running;
+
+	mutex_lock(&ctx->kdamond_lock);
+	running = ctx->kdamond != NULL;
+	mutex_unlock(&ctx->kdamond_lock);
+	return running;
+}
+
 static ssize_t damon_sysfs_kdamond_state_show(struct kobject *kobj,
 		struct kobj_attribute *attr, char *buf)
 {
-	/* TODO: Link with DAMON */
-	return sysfs_emit(buf, "off\n");
+	struct damon_sysfs_kdamond *kdamond = container_of(kobj,
+			struct damon_sysfs_kdamond, kobj);
+	struct damon_ctx *ctx = kdamond->damon_ctx;
+	bool running;
+
+	if (!ctx)
+		running = false;
+	else
+		running = damon_sysfs_ctx_running(ctx);
+
+	return sysfs_emit(buf, "%s\n", running ? "on" : "off");
+}
+
+static void damon_sysfs_destroy_targets(struct damon_ctx *ctx)
+{
+	struct damon_target *t, *next;
+
+	damon_for_each_target_safe(t, next, ctx) {
+		if (ctx->ops.id == DAMON_OPS_VADDR)
+			put_pid(t->pid);
+		damon_destroy_target(t);
+	}
+}
+
+static int damon_sysfs_set_targets(struct damon_ctx *ctx,
+		struct damon_sysfs_context *sysfs_ctx)
+{
+	struct damon_sysfs_targets *targets = sysfs_ctx->targets;
+	int i;
+
+	for (i = 0; i < targets->nr_targets; i++) {
+		struct damon_target *t;
+
+		t = damon_new_target();
+		if (!t) {
+			damon_sysfs_destroy_targets(ctx);
+			return -ENOMEM;
+		}
+		if (ctx->ops.id == DAMON_OPS_VADDR) {
+			t->pid = find_get_pid(targets->targets_arr[i]->pid);
+			if (!t->pid) {
+				damon_sysfs_destroy_targets(ctx);
+				return -EINVAL;
+			}
+		}
+		damon_add_target(ctx, t);
+	}
+	return 0;
+}
+
+static inline bool target_has_pid(const struct damon_ctx *ctx)
+{
+	return ctx->ops.id == DAMON_OPS_VADDR;
+}
+
+static void damon_sysfs_before_terminate(struct damon_ctx *ctx)
+{
+	struct damon_target *t, *next;
+
+	if (!target_has_pid(ctx))
+		return;
+
+	mutex_lock(&ctx->kdamond_lock);
+	damon_for_each_target_safe(t, next, ctx) {
+		put_pid(t->pid);
+		damon_destroy_target(t);
+	}
+	mutex_unlock(&ctx->kdamond_lock);
+}
+
+static struct damon_ctx *damon_sysfs_build_ctx(
+		struct damon_sysfs_context *sys_ctx)
+{
+	struct damon_ctx *ctx = damon_new_ctx();
+	struct damon_sysfs_attrs *sys_attrs = sys_ctx->attrs;
+	struct damon_sysfs_ul_range *sys_nr_regions = sys_attrs->nr_regions;
+	struct damon_sysfs_intervals *sys_intervals = sys_attrs->intervals;
+	int err;
+
+	if (!ctx)
+		return ERR_PTR(-ENOMEM);
+
+	err = damon_select_ops(ctx, sys_ctx->ops_id);
+	if (err)
+		goto out;
+
+	err = damon_set_attrs(ctx, sys_intervals->sample_us,
+			sys_intervals->aggr_us, sys_intervals->update_us,
+			sys_nr_regions->min, sys_nr_regions->max);
+	if (err)
+		goto out;
+	err = damon_sysfs_set_targets(ctx, sys_ctx);
+	if (err)
+		goto out;
+	ctx->callback.before_terminate = damon_sysfs_before_terminate;
+	return ctx;
+
+out:
+	damon_destroy_ctx(ctx);
+	return ERR_PTR(err);
 }
 
 static ssize_t damon_sysfs_kdamond_state_store(struct kobject *kobj,
 		struct kobj_attribute *attr, const char *buf, size_t count)
 {
-	/* TODO: Link with DAMON */
-	return count;
+	struct damon_sysfs_kdamond *kdamond = container_of(kobj,
+			struct damon_sysfs_kdamond, kobj);
+	struct damon_ctx *ctx;
+	ssize_t ret;
+
+	if (!mutex_trylock(&damon_sysfs_lock))
+		return -EBUSY;
+	if (!strncmp(buf, "on\n", count)) {
+		if (kdamond->damon_ctx &&
+				damon_sysfs_ctx_running(kdamond->damon_ctx)) {
+			ret = -EBUSY;
+			goto out;
+		}
+		if (kdamond->contexts->nr != 1) {
+			ret = -EINVAL;
+			goto out;
+		}
+
+		if (kdamond->damon_ctx)
+			damon_destroy_ctx(kdamond->damon_ctx);
+		kdamond->damon_ctx = NULL;
+
+		ctx = damon_sysfs_build_ctx(
+				kdamond->contexts->contexts_arr[0]);
+		if (IS_ERR(ctx)) {
+			ret = PTR_ERR(ctx);
+			goto out;
+		}
+		ret = damon_start(&ctx, 1, false);
+		if (ret) {
+			damon_destroy_ctx(ctx);
+			goto out;
+		}
+		kdamond->damon_ctx = ctx;
+	} else if (!strncmp(buf, "off\n", count)) {
+		if (!kdamond->damon_ctx) {
+			ret = -EINVAL;
+			goto out;
+		}
+		ret = damon_stop(&kdamond->damon_ctx, 1);
+		/*
+		 * kdamond->damon_ctx will be freed in next on, or
+		 * kdamonds_nr_store()
+		 */
+	} else {
+		ret = -EINVAL;
+	}
+out:
+	mutex_unlock(&damon_sysfs_lock);
+	if (!ret)
+		ret = count;
+	return ret;
 }
 
 static ssize_t damon_sysfs_kdamond_pid_show(struct kobject *kobj,
-- 
2.17.1