[PATCH -mm] tmpfs: test link accounting with O_TMPFILE

[Alexey Dobriyan <adobriyan@gmail.com>]

Mount tmpfs with "nr_inodes=3" for easy check.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

	-ENOTEST

	fold into tmpfs-fix-link-accounting-when-a-tmpfile-is-linked-in.patch

 tools/testing/selftests/Makefile                   |    1 
 tools/testing/selftests/tmpfs/.gitignore           |    1 
 tools/testing/selftests/tmpfs/Makefile             |    7 ++
 tools/testing/selftests/tmpfs/bug-link-o-tmpfile.c |   67 +++++++++++++++++++++
 4 files changed, 76 insertions(+)

--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -48,6 +48,7 @@ TARGETS += sysctl
 ifneq (1, $(quicktest))
 TARGETS += timers
 endif
+TARGETS += tmpfs
 TARGETS += user
 TARGETS += vm
 TARGETS += x86
new file mode 100644
--- /dev/null
+++ b/tools/testing/selftests/tmpfs/.gitignore
@@ -0,0 +1 @@
+/bug-link-o-tmpfile
new file mode 100644
--- /dev/null
+++ b/tools/testing/selftests/tmpfs/Makefile
@@ -0,0 +1,7 @@
+CFLAGS += -Wall -O2
+CFLAGS += -D_GNU_SOURCE
+
+TEST_GEN_PROGS :=
+TEST_GEN_PROGS += bug-link-o-tmpfile
+
+include ../lib.mk
new file mode 100644
--- /dev/null
+++ b/tools/testing/selftests/tmpfs/bug-link-o-tmpfile.c
@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2019 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/* Test that open(O_TMPFILE), linkat() doesn't screw accounting. */
+#include <errno.h>
+#include <sched.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <sys/mount.h>
+#include <unistd.h>
+
+int main(void)
+{
+	int fd;
+
+	if (unshare(CLONE_NEWNS) == -1) {
+		if (errno == ENOSYS || errno == EPERM) {
+			fprintf(stderr, "error: unshare, errno %d\n", errno);
+			return 4;
+		}
+		fprintf(stderr, "error: unshare, errno %d\n", errno);
+		return 1;
+	}
+	if (mount(NULL, "/", NULL, MS_PRIVATE|MS_REC, NULL) == -1) {
+		fprintf(stderr, "error: mount '/', errno %d\n", errno);
+		return 1;
+	}
+
+	/* Our heroes: 1 root inode, 1 O_TMPFILE inode, 1 permanent inode. */
+	if (mount(NULL, "/tmp", "tmpfs", 0, "nr_inodes=3") == -1) {
+		fprintf(stderr, "error: mount tmpfs, errno %d\n", errno);
+		return 1;
+	}
+
+	fd = openat(AT_FDCWD, "/tmp", O_WRONLY|O_TMPFILE, 0600);
+	if (fd == -1) {
+		fprintf(stderr, "error: open 1, errno %d\n", errno);
+		return 1;
+	}
+	if (linkat(fd, "", AT_FDCWD, "/tmp/1", AT_EMPTY_PATH) == -1) {
+		fprintf(stderr, "error: linkat, errno %d\n", errno);
+		return 1;
+	}
+	close(fd);
+
+	fd = openat(AT_FDCWD, "/tmp", O_WRONLY|O_TMPFILE, 0600);
+	if (fd == -1) {
+		fprintf(stderr, "error: open 2, errno %d\n", errno);
+		return 1;
+	}
+
+	return 0;
+}