The st_blocks field reported by fstat should reflect the number of
allocated 512-byte blocks for the guest memfd file.

Extend the fallocate test to verify that st_blocks is correctly updated
when memory is allocated or deallocated via
fallocate(FALLOC_FL_PUNCH_HOLE).

Add checks after each fallocate call to ensure that st_blocks increases on
allocation, decreases when a hole is punched, and is restored when the hole
is re-allocated. Also verify that st_blocks remains unchanged for failing
fallocate calls.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
 tools/testing/selftests/kvm/guest_memfd_test.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
index 638906298ed73..3381a556f397d 100644
--- a/tools/testing/selftests/kvm/guest_memfd_test.c
+++ b/tools/testing/selftests/kvm/guest_memfd_test.c
@@ -276,41 +276,58 @@ static void test_file_size(int fd, size_t total_size)
 	TEST_ASSERT_EQ(sb.st_blksize, page_size);
 }
 
+static void assert_st_blocks_matches_size(int fd, size_t expected_size)
+{
+	struct stat sb;
+
+	kvm_fstat(fd, &sb);
+	TEST_ASSERT_EQ(sb.st_blocks, expected_size / 512);
+}
+
 static void test_fallocate(int fd, size_t total_size)
 {
 	int ret;
 
 	ret = fallocate(fd, FALLOC_FL_KEEP_SIZE, 0, total_size);
 	TEST_ASSERT(!ret, "fallocate with aligned offset and size should succeed");
+	assert_st_blocks_matches_size(fd, total_size);
 
 	ret = fallocate(fd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE,
 			page_size - 1, page_size);
 	TEST_ASSERT(ret, "fallocate with unaligned offset should fail");
+	assert_st_blocks_matches_size(fd, total_size);
 
 	ret = fallocate(fd, FALLOC_FL_KEEP_SIZE, total_size, page_size);
 	TEST_ASSERT(ret, "fallocate beginning at total_size should fail");
+	assert_st_blocks_matches_size(fd, total_size);
 
 	ret = fallocate(fd, FALLOC_FL_KEEP_SIZE, total_size + page_size, page_size);
 	TEST_ASSERT(ret, "fallocate beginning after total_size should fail");
+	assert_st_blocks_matches_size(fd, total_size);
 
 	ret = fallocate(fd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE,
 			total_size, page_size);
 	TEST_ASSERT(!ret, "fallocate(PUNCH_HOLE) at total_size should succeed");
+	assert_st_blocks_matches_size(fd, total_size);
 
 	ret = fallocate(fd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE,
 			total_size + page_size, page_size);
 	TEST_ASSERT(!ret, "fallocate(PUNCH_HOLE) after total_size should succeed");
+	assert_st_blocks_matches_size(fd, total_size);
 
 	ret = fallocate(fd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE,
 			page_size, page_size - 1);
 	TEST_ASSERT(ret, "fallocate with unaligned size should fail");
+	assert_st_blocks_matches_size(fd, total_size);
 
 	ret = fallocate(fd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE,
 			page_size, page_size);
 	TEST_ASSERT(!ret, "fallocate(PUNCH_HOLE) with aligned offset and size should succeed");
+	assert_st_blocks_matches_size(fd, total_size - page_size);
 
 	ret = fallocate(fd, FALLOC_FL_KEEP_SIZE, page_size, page_size);
 	TEST_ASSERT(!ret, "fallocate to restore punched hole should succeed");
+	assert_st_blocks_matches_size(fd, total_size);
 }
 
 static void test_invalid_punch_hole(int fd, size_t total_size)

-- 
2.53.0.473.g4a7958ca14-goog