[PATCH 1/8] mm/damon/dbgfs: add and use mappings between 'schemes' action inputs and 'damos_action' values

[SeongJae Park <sj@kernel.org>]

DAMON debugfs interface assumes users will write 'damos_action' value
directly to the 'schemes' file.  This makes adding new 'damos_action' in
the middle of its definition breaks the backward compatibility of DAMON
debugfs interface, as values of some 'damos_action' could be changed.
To mitigate the situation, this commit adds mappings between the user
inputs and 'damos_action' value and makes DAMON debugfs code uses those.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/dbgfs.c | 64 +++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 50 insertions(+), 14 deletions(-)

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 5ae810927309..cb8a7e9926a4 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -97,6 +97,31 @@ static ssize_t dbgfs_attrs_write(struct file *file,
 	return ret;
 }
 
+/*
+ * Return corresponding dbgfs' scheme action value (int) for the given
+ * damos_action if the given damos_action value is valid and supported by
+ * dbgfs, negative error code otherwise.
+ */
+static int damos_action_to_dbgfs_scheme_action(enum damos_action action)
+{
+	switch (action) {
+	case DAMOS_WILLNEED:
+		return 0;
+	case DAMOS_COLD:
+		return 1;
+	case DAMOS_PAGEOUT:
+		return 2;
+	case DAMOS_HUGEPAGE:
+		return 3;
+	case DAMOS_NOHUGEPAGE:
+		return 4;
+	case DAMOS_STAT:
+		return 5;
+	default:
+		return -EINVAL;
+	}
+}
+
 static ssize_t sprint_schemes(struct damon_ctx *c, char *buf, ssize_t len)
 {
 	struct damos *s;
@@ -109,7 +134,7 @@ static ssize_t sprint_schemes(struct damon_ctx *c, char *buf, ssize_t len)
 				s->min_sz_region, s->max_sz_region,
 				s->min_nr_accesses, s->max_nr_accesses,
 				s->min_age_region, s->max_age_region,
-				s->action,
+				damos_action_to_dbgfs_scheme_action(s->action),
 				s->quota.ms, s->quota.sz,
 				s->quota.reset_interval,
 				s->quota.weight_sz,
@@ -160,18 +185,27 @@ static void free_schemes_arr(struct damos **schemes, ssize_t nr_schemes)
 	kfree(schemes);
 }
 
-static bool damos_action_valid(int action)
+/*
+ * Return corresponding damos_action for the given dbgfs input for a scheme
+ * action if the input is valid, negative error code otherwise.
+ */
+static enum damos_action dbgfs_scheme_action_to_damos_action(int dbgfs_action)
 {
-	switch (action) {
-	case DAMOS_WILLNEED:
-	case DAMOS_COLD:
-	case DAMOS_PAGEOUT:
-	case DAMOS_HUGEPAGE:
-	case DAMOS_NOHUGEPAGE:
-	case DAMOS_STAT:
-		return true;
+	switch (dbgfs_action) {
+	case 0:
+		return DAMOS_WILLNEED;
+	case 1:
+		return DAMOS_COLD;
+	case 2:
+		return DAMOS_PAGEOUT;
+	case 3:
+		return DAMOS_HUGEPAGE;
+	case 4:
+		return DAMOS_NOHUGEPAGE;
+	case 5:
+		return DAMOS_STAT;
 	default:
-		return false;
+		return -EINVAL;
 	}
 }
 
@@ -189,7 +223,8 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
 	int pos = 0, parsed, ret;
 	unsigned long min_sz, max_sz;
 	unsigned int min_nr_a, max_nr_a, min_age, max_age;
-	unsigned int action;
+	unsigned int action_input;
+	enum damos_action action;
 
 	schemes = kmalloc_array(max_nr_schemes, sizeof(scheme),
 			GFP_KERNEL);
@@ -204,7 +239,7 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
 		ret = sscanf(&str[pos],
 				"%lu %lu %u %u %u %u %u %lu %lu %lu %u %u %u %u %lu %lu %lu %lu%n",
 				&min_sz, &max_sz, &min_nr_a, &max_nr_a,
-				&min_age, &max_age, &action, &quota.ms,
+				&min_age, &max_age, &action_input, &quota.ms,
 				&quota.sz, &quota.reset_interval,
 				&quota.weight_sz, &quota.weight_nr_accesses,
 				&quota.weight_age, &wmarks.metric,
@@ -212,7 +247,8 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
 				&wmarks.low, &parsed);
 		if (ret != 18)
 			break;
-		if (!damos_action_valid(action))
+		action = dbgfs_scheme_action_to_damos_action(action_input);
+		if ((int)action < 0)
 			goto fail;
 
 		if (min_sz > max_sz || min_nr_a > max_nr_a || min_age > max_age)
-- 
2.25.1