tools/testing/selftests/memfd/fuse_test.c

Source file repositories/reference/linux-study-clean/tools/testing/selftests/memfd/fuse_test.c

File Facts

System
Linux kernel
Corpus path
tools/testing/selftests/memfd/fuse_test.c
Extension
.c
Size
7714 bytes
Lines
332
Domain
Support Tooling And Documentation
Bucket
tools
Inferred role
Support Tooling And Documentation: implementation source
Status
source implementation candidate

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

if (!strcmp(argv[2], "hugetlbfs")) {
			unsigned long hpage_size = default_huge_page_size();

			if (!hpage_size) {
				printf("Unable to determine huge page size\n");
				abort();
			}

			hugetlbfs_test = 1;
			mfd_def_size = hpage_size * 2;
		} else {
			printf("Unknown option: %s\n", argv[2]);
			abort();
		}
	}

	zero = calloc(sizeof(*zero), mfd_def_size);

	/* open FUSE memfd file for GUP testing */
	printf("opening: %s\n", argv[1]);
	fd = open(argv[1], O_RDONLY | O_CLOEXEC);
	if (fd < 0) {
		printf("cannot open(\"%s\"): %m\n", argv[1]);
		abort();
	}

	/* create new memfd-object */
	mfd = mfd_assert_new("kern_memfd_fuse",
			     mfd_def_size,
			     MFD_CLOEXEC | MFD_ALLOW_SEALING);

	/* mmap memfd-object for writing */
	p = mfd_assert_mmap_shared(mfd);

	/* pass mfd+mapping to a separate sealing-thread which tries to seal
	 * the memfd objects with SEAL_WRITE while we write into it */
	global_mfd = mfd;
	global_p = p;
	pid = spawn_sealing_thread();

	/* Use read() on the FUSE file to read into our memory-mapped memfd
	 * object. This races the other thread which tries to seal the
	 * memfd-object.
	 * If @fd is on the memfd-fake-FUSE-FS, the read() is delayed by 1s.
	 * This guarantees that the receive-buffer is pinned for 1s until the
	 * data is written into it. The racing ADD_SEALS should thus fail as
	 * the pages are still pinned. */
	r = read(fd, p, mfd_def_size);
	if (r < 0) {
		printf("read() failed: %m\n");
		abort();
	} else if (!r) {
		printf("unexpected EOF on read()\n");
		abort();
	}

	was_sealed = mfd_assert_get_seals(mfd) & F_SEAL_WRITE;

	/* Wait for sealing-thread to finish and verify that it
	 * successfully sealed the file after the second try. */
	join_sealing_thread(pid);
	mfd_assert_has_seals(mfd, F_SEAL_WRITE);

	/* *IF* the memfd-object was sealed at the time our read() returned,
	 * then the kernel did a page-replacement or canceled the read() (or
	 * whatever magic it did..). In that case, the memfd object is still
	 * all zero.
	 * In case the memfd-object was *not* sealed, the read() was successful
	 * and the memfd object must *not* be all zero.
	 * Note that in real scenarios, there might be a mixture of both, but
	 * in this test-cases, we have explicit 200ms delays which should be
	 * enough to avoid any in-flight writes. */

	p = mfd_assert_mmap_private(mfd);
	if (was_sealed && memcmp(p, zero, mfd_def_size)) {
		printf("memfd sealed during read() but data not discarded\n");
		abort();
	} else if (!was_sealed && !memcmp(p, zero, mfd_def_size)) {
		printf("memfd sealed after read() but data discarded\n");
		abort();
	}

	close(mfd);
	close(fd);

	printf("fuse: DONE\n");
	free(zero);

	return 0;
}

Annotation

Implementation Notes