[PATCH 6.1.y] selftests/vm: fix undefined reference of the `default_huge_page_size`

[Andrey Kalachev]

The commit a584c7734a4d ("selftests: mm: fix map_hugetlb failure on
64K page size systems") backported the fix from v6.8 to stable v6.1.
The patch uses default_huge_page_size() function, which definition
moved into vm_util.[ch] by commit bd4d67e76f699 ("selftests/mm:
merge default_huge_page_size() into one") merged to upsream since
v6.4. However, in v6.1 common definition/declaration for the
default_huge_page_size() we doesn't have, the following build
error is seen:

map_hugetlb.c:79:25: warning: implicit declaration of function
‘default_huge_page_size’ [-Wimplicit-function-declaration]
   79 |         hugepage_size = default_huge_page_size();
      |                         ^~~~~~~~~~~~~~~~~~~~~~
/usr/bin/ld: /tmp/ccx95BZz.o: in function `main':
map_hugetlb.c:(.text+0x104): undefined reference to
`default_huge_page_size'

Place default_huge_page_size() function body into map_hugetlb.c
to fix this issue.

Fixes: a584c7734a4d ("selftests: mm: fix map_hugetlb failure on 64K page size 
systems")
Signed-off-by: Andrey Kalachev <kalac...@swemel.ru>
---
 tools/testing/selftests/vm/map_hugetlb.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/tools/testing/selftests/vm/map_hugetlb.c 
b/tools/testing/selftests/vm/map_hugetlb.c
index c65c55b7a789..5826c50b6736 100644
--- a/tools/testing/selftests/vm/map_hugetlb.c
+++ b/tools/testing/selftests/vm/map_hugetlb.c
@@ -67,6 +67,30 @@ static int read_bytes(char *addr, size_t length)
        return 0;
 }
 
+/*
+ * default_huge_page_size copied from mlock2-tests.c
+ */
+unsigned long default_huge_page_size(void)
+{
+       unsigned long hps = 0;
+       char *line = NULL;
+       size_t linelen = 0;
+       FILE *f = fopen("/proc/meminfo", "r");
+
+       if (!f)
+               return 0;
+       while (getline(&line, &linelen, f) > 0) {
+               if (sscanf(line, "Hugepagesize:       %lu kB", &hps) == 1) {
+                       hps <<= 10;
+                       break;
+               }
+       }
+
+       free(line);
+       fclose(f);
+       return hps;
+}
+
 int main(int argc, char **argv)
 {
        void *addr;
-- 
2.39.5