[PATCH 1/4] mm/damon/dbgfs/init_regions: Use target index instead of target id

[SeongJae Park <sj@kernel.org>]

Target id is a 'unsigned long' data, which can be interpreted
differently by each monitoring primitives.  For example, it means
'struct pid *' for the virtual address spaces monitoring, while it means
nothing but an integer to be displayed to debugfs interface users for
the physical address space monitoring.  It's flexible but makes code
ugly and type-unsafe[1].

To be prepared for eventual removal of the concept, this commit removes
a use case of the concept in 'init_regions' debugfs file handling.  In
detail, this commit replaces use of the id with the index of each target
in the context's targets list.

[1] https://lore.kernel.org/linux-mm/20211013154535.4aaeaaf9d0182922e405dd1e@linux-foundation.org/

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/dbgfs-test.h | 20 ++++++++++----------
 mm/damon/dbgfs.c      | 25 ++++++++++++-------------
 2 files changed, 22 insertions(+), 23 deletions(-)

diff --git a/mm/damon/dbgfs-test.h b/mm/damon/dbgfs-test.h
index 86b9f9528231..00bff058fe08 100644
--- a/mm/damon/dbgfs-test.h
+++ b/mm/damon/dbgfs-test.h
@@ -113,19 +113,19 @@ static void damon_dbgfs_test_set_init_regions(struct kunit *test)
 {
 	struct damon_ctx *ctx = damon_new_ctx();
 	unsigned long ids[] = {1, 2, 3};
-	/* Each line represents one region in ``<target id> <start> <end>`` */
-	char * const valid_inputs[] = {"2 10 20\n 2   20 30\n2 35 45",
-		"2 10 20\n",
-		"2 10 20\n1 39 59\n1 70 134\n  2  20 25\n",
+	/* Each line represents one region in ``<target idx> <start> <end>`` */
+	char * const valid_inputs[] = {"1 10 20\n 1   20 30\n1 35 45",
+		"1 10 20\n",
+		"1 10 20\n0 39 59\n0 70 134\n  1  20 25\n",
 		""};
 	/* Reading the file again will show sorted, clean output */
-	char * const valid_expects[] = {"2 10 20\n2 20 30\n2 35 45\n",
-		"2 10 20\n",
-		"1 39 59\n1 70 134\n2 10 20\n2 20 25\n",
+	char * const valid_expects[] = {"1 10 20\n1 20 30\n1 35 45\n",
+		"1 10 20\n",
+		"0 39 59\n0 70 134\n1 10 20\n1 20 25\n",
 		""};
-	char * const invalid_inputs[] = {"4 10 20\n",	/* target not exists */
-		"2 10 20\n 2 14 26\n",		/* regions overlap */
-		"1 10 20\n2 30 40\n 1 5 8"};	/* not sorted by address */
+	char * const invalid_inputs[] = {"3 10 20\n",	/* target not exists */
+		"1 10 20\n 1 14 26\n",		/* regions overlap */
+		"0 10 20\n1 30 40\n 0 5 8"};	/* not sorted by address */
 	char *input, *expect;
 	int i, rc;
 	char buf[256];
diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 5b899601e56c..3f65af04e4e6 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -440,18 +440,20 @@ static ssize_t sprint_init_regions(struct damon_ctx *c, char *buf, ssize_t len)
 {
 	struct damon_target *t;
 	struct damon_region *r;
+	int target_idx = 0;
 	int written = 0;
 	int rc;
 
 	damon_for_each_target(t, c) {
 		damon_for_each_region(r, t) {
 			rc = scnprintf(&buf[written], len - written,
-					"%lu %lu %lu\n",
-					t->id, r->ar.start, r->ar.end);
+					"%d %lu %lu\n",
+					target_idx, r->ar.start, r->ar.end);
 			if (!rc)
 				return -ENOMEM;
 			written += rc;
 		}
+		target_idx++;
 	}
 	return written;
 }
@@ -485,22 +487,19 @@ static ssize_t dbgfs_init_regions_read(struct file *file, char __user *buf,
 	return len;
 }
 
-static int add_init_region(struct damon_ctx *c,
-			 unsigned long target_id, struct damon_addr_range *ar)
+static int add_init_region(struct damon_ctx *c, int target_idx,
+		struct damon_addr_range *ar)
 {
 	struct damon_target *t;
 	struct damon_region *r, *prev;
-	unsigned long id;
+	unsigned long idx = 0;
 	int rc = -EINVAL;
 
 	if (ar->start >= ar->end)
 		return -EINVAL;
 
 	damon_for_each_target(t, c) {
-		id = t->id;
-		if (targetid_is_pid(c))
-			id = (unsigned long)pid_vnr((struct pid *)id);
-		if (id == target_id) {
+		if (idx++ == target_idx) {
 			r = damon_new_region(ar->start, ar->end);
 			if (!r)
 				return -ENOMEM;
@@ -523,7 +522,7 @@ static int set_init_regions(struct damon_ctx *c, const char *str, ssize_t len)
 	struct damon_target *t;
 	struct damon_region *r, *next;
 	int pos = 0, parsed, ret;
-	unsigned long target_id;
+	int target_idx;
 	struct damon_addr_range ar;
 	int err;
 
@@ -533,11 +532,11 @@ static int set_init_regions(struct damon_ctx *c, const char *str, ssize_t len)
 	}
 
 	while (pos < len) {
-		ret = sscanf(&str[pos], "%lu %lu %lu%n",
-				&target_id, &ar.start, &ar.end, &parsed);
+		ret = sscanf(&str[pos], "%d %lu %lu%n",
+				&target_idx, &ar.start, &ar.end, &parsed);
 		if (ret != 3)
 			break;
-		err = add_init_region(c, target_id, &ar);
+		err = add_init_region(c, target_idx, &ar);
 		if (err)
 			goto fail;
 		pos += parsed;
-- 
2.17.1