[PATCH v2 1/3] selftests/mm: handle EINVAL when configuring gigantic hugepages

[Sayali Patil <sayalip@linux.ibm.com>]

Some MM selftests attempt to configure the amount of
HugeTLB pages of different sizes by writing to nr_hugepages.

PowerPC hash MMU pSeries systems advertise gigantic hugepage sizes
but do not support runtime allocation of such pages, writes
to the corresponding nr_hugepages file fail with -EINVAL.
This causes the test to bail out even though the failure is due
to a platform limitation rather than the
functionality being tested.

Treat -EINVAL from the sysfs write as a skipped configuration request
and continue running the test instead of failing.

Before patch:
   -------------------------
   running ./hugetlb-madvise
   -------------------------
   TAP version 13
   1..1
     [INFO] detected hugetlb page size: 16777216 KiB
     [INFO] detected hugetlb page size: 16384 KiB
    ok 1 MADV_DONTNEED and MADV_REMOVE on hugetlb
    Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
    Bail out! /sys/kernel/mm/hugepages/hugepages-16777216kB/nr_hugepages
    write(0) failed: Invalid argument
    Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0
    [FAIL]

After patch:
   -------------------------
   running ./hugetlb-madvise
   -------------------------
   TAP version 13
   1..1
    [INFO] detected hugetlb page size: 16777216 KiB
    [INFO] detected hugetlb page size: 16384 KiB
   ok 1 MADV_DONTNEED and MADV_REMOVE on hugetlb
   Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
   /sys/kernel/mm/hugepages/hugepages-16777216kB/nr_hugepages
   write(0) failed: Invalid argument
   [PASS]

Fixes: 27477b28b74f ("selftests/mm: hugepage_settings: add APIs to get and set nr_hugepages")
Signed-off-by: Sayali Patil <sayalip@linux.ibm.com>
---
 .../testing/selftests/mm/hugepage_settings.c  | 32 ++++++++++++++++++-
 .../testing/selftests/mm/hugepage_settings.h  |  1 +
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/hugepage_settings.c b/tools/testing/selftests/mm/hugepage_settings.c
index 2eab2110ac6a..ce38ae3da01a 100644
--- a/tools/testing/selftests/mm/hugepage_settings.c
+++ b/tools/testing/selftests/mm/hugepage_settings.c
@@ -422,6 +422,36 @@ static void hugetlb_sysfs_path(char *buf, size_t buflen,
 		 size / 1024, attr);
 }
 
+void hugetlb_write_num(const char *path, unsigned long num)
+{
+	int fd, saved_errno;
+	ssize_t numwritten;
+	char buf[21];
+
+	sprintf(buf, "%lu", num);
+
+	fd = open(path, O_WRONLY);
+	if (fd == -1)
+		ksft_exit_fail_msg("%s open failed: %s\n", path, strerror(errno));
+
+	numwritten = write(fd, buf, strlen(buf));
+	saved_errno = errno;
+	close(fd);
+	errno = saved_errno;
+
+	/* Treat EINVAL as a skipped configuration (e.g., unsupported gigantic pages) */
+	if (numwritten < 0 && errno == EINVAL) {
+		ksft_print_msg("%s write(%s) failed: %s\n", path, buf, strerror(errno));
+		return;
+	}
+
+	if (numwritten < 0)
+		ksft_exit_fail_msg("%s write(%s) failed: %s\n", path, buf, strerror(errno));
+	if (numwritten != strlen(buf))
+		ksft_exit_fail_msg("%s write(%s) is truncated, expected %zu bytes, got %zd bytes\n",
+				   path, buf, strlen(buf), numwritten);
+}
+
 unsigned long hugetlb_nr_pages(unsigned long size)
 {
 	char path[PATH_MAX];
@@ -437,7 +467,7 @@ void hugetlb_set_nr_pages(unsigned long size, unsigned long nr)
 
 	hugetlb_sysfs_path(path, sizeof(path), size, "nr_hugepages");
 
-	write_num(path, nr);
+	hugetlb_write_num(path, nr);
 }
 
 unsigned long hugetlb_free_pages(unsigned long size)
diff --git a/tools/testing/selftests/mm/hugepage_settings.h b/tools/testing/selftests/mm/hugepage_settings.h
index 726c73c43c05..390fcc483b9e 100644
--- a/tools/testing/selftests/mm/hugepage_settings.h
+++ b/tools/testing/selftests/mm/hugepage_settings.h
@@ -95,6 +95,7 @@ bool thp_is_enabled(void);
 int detect_hugetlb_page_sizes(unsigned long sizes[], int max);
 unsigned long default_huge_page_size(void);
 
+void hugetlb_write_num(const char *path, unsigned long num);
 unsigned long hugetlb_nr_pages(unsigned long size);
 void hugetlb_set_nr_pages(unsigned long size, unsigned long nr);
 unsigned long hugetlb_free_pages(unsigned long size);
-- 
2.52.0