hugetlb_dio test uses sub-page offsets (pagesize / 2) to verify that
hugepages used as DIO user buffers are correctly unpinned at completion.

However, on filesystems with a logical block size larger than half the
page size (e.g., 4K-sector block devices), these unaligned DIO writes
are rejected with -EINVAL, causing the test to fail unexpectedly.

Add get_dio_alignment() to query the filesystem's required DIO alignment
via statx(STATX_DIOALIGN) and pass it to run_dio_using_hugetlb(). Skip
individual test cases whose write length is not a multiple of the
alignment, so that aligned cases are still tested.

=== Reproduce Steps ===

  # dd if=/dev/zero of=/tmp/test.img bs=1M count=512
  # losetup --sector-size 4096 /dev/loop0 /tmp/test.img
  # mkfs.xfs /dev/loop0
  # mkdir -p /mnt/dio_test
  # mount /dev/loop0 /mnt/dio_test

  // Modify test to open /mnt/dio_test and rebuild it:
  -       fd = open("/tmp", O_TMPFILE | O_RDWR | O_DIRECT, 0664);
  +       fd = open("/mnt/dio_test", O_TMPFILE | O_RDWR | O_DIRECT, 0664);

  # getconf PAGESIZE
  4096

  # echo 100 >/proc/sys/vm/nr_hugepages

  # ./hugetlb_dio
  TAP version 13
  1..4
  # No. Free pages before allocation : 100
  # No. Free pages after munmap : 100
  ok 1 free huge pages from 0-12288
  Bail out! Error writing to file
  : Invalid argument (22)
  # Planned tests != run tests (4 != 1)
  # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0

Signed-off-by: Li Wang <liwang@redhat.com>
---

Notes:
    v2:
    	- Pass dio_align as a parameter to run_dio_using_hugetlb()
    	  instead of generally page_size/2 alignment check.

 tools/testing/selftests/mm/hugetlb_dio.c | 56 +++++++++++++++++-------
 1 file changed, 40 insertions(+), 16 deletions(-)

diff --git a/tools/testing/selftests/mm/hugetlb_dio.c b/tools/testing/selftests/mm/hugetlb_dio.c
index 9ac62eb4c97d..638a8abe3ae2 100644
--- a/tools/testing/selftests/mm/hugetlb_dio.c
+++ b/tools/testing/selftests/mm/hugetlb_dio.c
@@ -20,7 +20,35 @@
 #include "vm_util.h"
 #include "kselftest.h"
 
-void run_dio_using_hugetlb(unsigned int start_off, unsigned int end_off)
+#ifndef STATX_DIOALIGN
+#define STATX_DIOALIGN		0x00002000U
+#endif
+
+unsigned int get_dio_alignment(void)
+{
+	int fd, ret;
+	struct statx stx;
+	unsigned int dio_align = 1;
+
+	fd = open("/tmp", O_TMPFILE | O_RDWR | O_DIRECT, 0664);
+	if (fd < 0)
+		ksft_exit_skip("Unable to allocate file: %s\n", strerror(errno));
+
+	ret = statx(fd, "", AT_EMPTY_PATH, STATX_DIOALIGN, &stx);
+	if (ret < 0) {
+		ksft_perror("statx() failed");
+	} else if ((stx.stx_mask & STATX_DIOALIGN) &&
+			stx.stx_dio_offset_align) {
+		dio_align = stx.stx_dio_offset_align;
+	}
+
+	close(fd);
+
+	return dio_align;
+}
+
+void run_dio_using_hugetlb(unsigned int start_off, unsigned int end_off,
+			unsigned int dio_align)
 {
 	int fd;
 	char *buffer =  NULL;
@@ -33,6 +61,11 @@ void run_dio_using_hugetlb(unsigned int start_off, unsigned int end_off)
 	const int mmap_prot  = PROT_READ | PROT_WRITE;
 
 	writesize = end_off - start_off;
+	if (writesize % dio_align != 0) {
+		ksft_test_result_skip("DIO alignment (%u) incompatible with offset %zu\n",
+				dio_align, writesize);
+		return;
+	}
 
 	/* Get the default huge page size */
 	h_pagesize = default_huge_page_size();
@@ -89,37 +122,28 @@ void run_dio_using_hugetlb(unsigned int start_off, unsigned int end_off)
 
 int main(void)
 {
-	size_t pagesize = 0;
-	int fd;
+	size_t pagesize = psize();
+	unsigned int dio_align = get_dio_alignment();
 
 	ksft_print_header();
 
-	/* Open the file to DIO */
-	fd = open("/tmp", O_TMPFILE | O_RDWR | O_DIRECT, 0664);
-	if (fd < 0)
-		ksft_exit_skip("Unable to allocate file: %s\n", strerror(errno));
-	close(fd);
-
 	/* Check if huge pages are free */
 	if (!get_free_hugepages())
 		ksft_exit_skip("No free hugepage, exiting\n");
 
 	ksft_set_plan(4);
 
-	/* Get base page size */
-	pagesize  = psize();
-
 	/* start and end is aligned to pagesize */
-	run_dio_using_hugetlb(0, (pagesize * 3));
+	run_dio_using_hugetlb(0, (pagesize * 3), dio_align);
 
 	/* start is aligned but end is not aligned */
-	run_dio_using_hugetlb(0, (pagesize * 3) - (pagesize / 2));
+	run_dio_using_hugetlb(0, (pagesize * 3) - (pagesize / 2), dio_align);
 
 	/* start is unaligned and end is aligned */
-	run_dio_using_hugetlb(pagesize / 2, (pagesize * 3));
+	run_dio_using_hugetlb(pagesize / 2, (pagesize * 3), dio_align);
 
 	/* both start and end are unaligned */
-	run_dio_using_hugetlb(pagesize / 2, (pagesize * 3) + (pagesize / 2));
+	run_dio_using_hugetlb(pagesize / 2, (pagesize * 3) + (pagesize / 2), dio_align);
 
 	ksft_finished();
 }
-- 
2.53.0