[PATCH v2] selftests/mm: read memory information without popen

[Warren Xiong <warren.xiong@ugreen.com>]

read_memory_info() invokes two shell pipelines to obtain MemFree and
Hugepagesize from /proc/meminfo. It does not check whether popen()
returns NULL before passing the result to fgets(), and it does not call
pclose() when fgets() fails.

Open /proc/meminfo directly and obtain both values in a single pass.
This removes the unchecked NULL path, closes the file on all paths, and
avoids dependencies on external commands.

The compaction test continues to pass after this change.

Signed-off-by: Warren Xiong <warren.xiong@ugreen.com>
---
Changes in v2:
- Replace the two boolean flags with a hit counter, as suggested by
  David Hildenbrand.

v1: https://lore.kernel.org/1785720615-5826-1-git-send-email-warren.xiong@ugreen.com/

 tools/testing/selftests/mm/compaction_test.c | 38 +++++++++++++++-------------
 1 file changed, 21 insertions(+), 17 deletions(-)

diff --git a/tools/testing/selftests/mm/compaction_test.c b/tools/testing/selftests/mm/compaction_test.c
index 5b58258..30d4ace 100644
--- a/tools/testing/selftests/mm/compaction_test.c
+++ b/tools/testing/selftests/mm/compaction_test.c
@@ -29,30 +29,34 @@ struct map_list {
 
 int read_memory_info(unsigned long *memfree, unsigned long *hugepagesize)
 {
-	char  buffer[256] = {0};
-	char *cmd = "cat /proc/meminfo | grep -i memfree | grep -o '[0-9]*'";
-	FILE *cmdfile = popen(cmd, "r");
+	char buffer[256];
+	int found = 0;
+	FILE *file;
+	int ret = -1;
 
-	if (!(fgets(buffer, sizeof(buffer), cmdfile))) {
-		ksft_print_msg("Failed to read meminfo: %s\n", strerror(errno));
+	file = fopen("/proc/meminfo", "r");
+	if (!file) {
+		ksft_print_msg("Failed to open /proc/meminfo: %s\n",
+			       strerror(errno));
 		return -1;
 	}
 
-	pclose(cmdfile);
-
-	*memfree = atoll(buffer);
-	cmd = "cat /proc/meminfo | grep -i hugepagesize | grep -o '[0-9]*'";
-	cmdfile = popen(cmd, "r");
-
-	if (!(fgets(buffer, sizeof(buffer), cmdfile))) {
-		ksft_print_msg("Failed to read meminfo: %s\n", strerror(errno));
-		return -1;
+	while (fgets(buffer, sizeof(buffer), file) && found != 2) {
+		if (sscanf(buffer, "MemFree: %lu kB", memfree) == 1 ||
+		    sscanf(buffer, "Hugepagesize: %lu kB", hugepagesize) == 1)
+			found++;
 	}
 
-	pclose(cmdfile);
-	*hugepagesize = atoll(buffer);
+	if (ferror(file))
+		ksft_print_msg("Failed to read /proc/meminfo: %s\n",
+			       strerror(errno));
+	else if (found != 2)
+		ksft_print_msg("Failed to parse /proc/meminfo\n");
+	else
+		ret = 0;
 
-	return 0;
+	fclose(file);
+	return ret;
 }
 
 int prereq(void)
-- 
2.7.4