[PATCH 2/5] userfaultfd/selftests: use memfd_create for shmem test type

[Axel Rasmussen <axelrasmussen@xxxxxxxxxx>]

This is a preparatory commit. In the future, we want to be able to setup
alias mappings for area_src and area_dst in the shmem test, like we do
in the hugetlb_shared test. With a VMA obtained via
mmap(MAP_ANONYMOUS | MAP_SHARED), it isn't clear how to do this.

So, mmap() with an fd, so we can create alias mappings. Use memfd_create
instead of actually passing in a tmpfs path like hugetlb does, since
it's more convenient / simpler to run, and works just as well.

Future commits will:

1. Setup the alias mappings.
2. Extend our tests to actually take advantage of this, to test new
   userfaultfd behavior being introduced in this series.

Also, a small fix in the area we're changing: when the hugetlb setup
fails in main(), pass in the right argv[] so we actually print out the
hugetlb file path.

Signed-off-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
---
 tools/testing/selftests/vm/userfaultfd.c | 35 ++++++++++++++++++++----
 1 file changed, 30 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
index f5ab5e0312e7..859398efb4fe 100644
--- a/tools/testing/selftests/vm/userfaultfd.c
+++ b/tools/testing/selftests/vm/userfaultfd.c
@@ -85,6 +85,7 @@ static bool test_uffdio_wp = false;
 static bool test_uffdio_minor = false;
 
 static bool map_shared;
+static int shm_fd;
 static int huge_fd;
 static char *huge_fd_off0;
 static unsigned long long *count_verify;
@@ -297,12 +298,20 @@ static int shmem_release_pages(char *rel_area)
 
 static void shmem_allocate_area(void **alloc_area)
 {
+	unsigned long offset =
+		alloc_area == (void **)&area_src ? 0 : nr_pages * page_size;
+
 	*alloc_area = mmap(NULL, nr_pages * page_size, PROT_READ | PROT_WRITE,
-			   MAP_ANONYMOUS | MAP_SHARED, -1, 0);
+			   MAP_SHARED, shm_fd, offset);
 	if (*alloc_area == MAP_FAILED) {
-		fprintf(stderr, "shared memory mmap failed\n");
-		*alloc_area = NULL;
+		perror("mmap of memfd failed");
+		goto fail;
 	}
+
+	return;
+
+fail:
+	*alloc_area = NULL;
 }
 
 struct uffd_test_ops {
@@ -1672,15 +1681,31 @@ int main(int argc, char **argv)
 			usage();
 		huge_fd = open(argv[4], O_CREAT | O_RDWR, 0755);
 		if (huge_fd < 0) {
-			fprintf(stderr, "Open of %s failed", argv[3]);
+			fprintf(stderr, "Open of %s failed", argv[4]);
 			perror("open");
 			exit(1);
 		}
 		if (ftruncate(huge_fd, 0)) {
-			fprintf(stderr, "ftruncate %s to size 0 failed", argv[3]);
+			fprintf(stderr, "ftruncate %s to size 0 failed", argv[4]);
 			perror("ftruncate");
 			exit(1);
 		}
+	} else if (test_type == TEST_SHMEM) {
+		shm_fd = memfd_create(argv[0], 0);
+		if (shm_fd < 0) {
+			perror("memfd_create");
+			exit(1);
+		}
+		if (ftruncate(shm_fd, nr_pages * page_size * 2)) {
+			perror("ftruncate");
+			exit(1);
+		}
+		if (fallocate(shm_fd,
+			      FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, 0,
+			      nr_pages * page_size * 2)) {
+			perror("fallocate");
+			exit(1);
+		}
 	}
 	printf("nr_pages: %lu, nr_pages_per_cpu: %lu\n",
 	       nr_pages, nr_pages_per_cpu);
-- 
2.30.0.617.g56c4b15f3c-goog