selftests/mm: vm_util: split up /proc/self/smaps parsing

Upcoming changes want to reuse the /proc/self/smaps parsing logic to parse
the VmFlags field.

As that works differently from the currently parsed HugePage counters,
split up the logic so common functionality can be shared.

While reworking this code, also use the correct sscanf placeholder for the
"uint64_t thp" variable.

Link: https://lkml.kernel.org/r/20250114-virtual_address_range-tests-v4-3-6fd7269934a5@linutronix.de
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: kernel test robot <oliver.sang@intel.com>
Cc: Shuah Khan (Samsung OSG) <shuah@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: t-8ch

tools/testing/selftests/mm/vm_util.c

@@ -2,6 +2,7 @@
 #include <string.h>
 #include <fcntl.h>
 #include <dirent.h>
+#include <inttypes.h>
 #include <sys/ioctl.h>
 #include <linux/userfaultfd.h>
 #include <linux/fs.h>
@@ -193,13 +194,11 @@ unsigned long rss_anon(void)
 	return rss_anon;
 }
 
-bool __check_huge(void *addr, char *pattern, int nr_hpages,
-		  uint64_t hpage_size)
+char *__get_smap_entry(void *addr, const char *pattern, char *buf, size_t len)
 {
-	uint64_t thp = -1;
 	int ret;
 	FILE *fp;
-	char buffer[MAX_LINE_LENGTH];
+	char *entry = NULL;
 	char addr_pattern[MAX_LINE_LENGTH];
 
 	ret = snprintf(addr_pattern, MAX_LINE_LENGTH, "%08lx-",
@@ -211,23 +210,40 @@ bool __check_huge(void *addr, char *pattern, int nr_hpages,
 	if (!fp)
 		ksft_exit_fail_msg("%s: Failed to open file %s\n", __func__, SMAP_FILE_PATH);
 
-	if (!check_for_pattern(fp, addr_pattern, buffer, sizeof(buffer)))
+	if (!check_for_pattern(fp, addr_pattern, buf, len))
 		goto err_out;
 
-	/*
-	 * Fetch the pattern in the same block and check the number of
-	 * hugepages.
-	 */
-	if (!check_for_pattern(fp, pattern, buffer, sizeof(buffer)))
+	/* Fetch the pattern in the same block */
+	if (!check_for_pattern(fp, pattern, buf, len))
 		goto err_out;
 
-	snprintf(addr_pattern, MAX_LINE_LENGTH, "%s%%9ld kB", pattern);
+	/* Trim trailing newline */
+	entry = strchr(buf, '\n');
+	if (entry)
+		*entry = '\0';
 
-	if (sscanf(buffer, addr_pattern, &thp) != 1)
-		ksft_exit_fail_msg("Reading smap error\n");
+	entry = buf + strlen(pattern);
 
 err_out:
 	fclose(fp);
+	return entry;
+}
+
+bool __check_huge(void *addr, char *pattern, int nr_hpages,
+		  uint64_t hpage_size)
+{
+	char buffer[MAX_LINE_LENGTH];
+	uint64_t thp = -1;
+	char *entry;
+
+	entry = __get_smap_entry(addr, pattern, buffer, sizeof(buffer));
+	if (!entry)
+		goto err_out;
+
+	if (sscanf(entry, "%9" SCNu64 " kB", &thp) != 1)
+		ksft_exit_fail_msg("Reading smap error\n");
+
+err_out:
 	return thp == (nr_hpages * (hpage_size >> 10));
 }