selftests/bpf: add file dynptr tests

Introducing selftests for validating file-backed dynptr works as
expected.
 * validate implementation supports dynptr slice and read operations
 * validate destructors should be paired with initializers
 * validate sleepable progs can page in.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20251026203853.135105-11-mykyta.yatsenko5@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 113 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/file_reader.c b/tools/testing/selftests/bpf/prog_tests/file_reader.c
new file mode 100644
index 000000000000..2a034d43b73e
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/file_reader.c
@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#include <test_progs.h>
+#include <network_helpers.h>
+#include "file_reader.skel.h"
+#include "file_reader_fail.skel.h"
+#include <dlfcn.h>
+#include <sys/mman.h>
+
+const char *user_ptr = "hello world";
+char file_contents[256000];
+
+void *get_executable_base_addr(void)
+{
+	Dl_info info;
+
+	if (!dladdr((void *)&get_executable_base_addr, &info)) {
+		fprintf(stderr, "dladdr failed\n");
+		return NULL;
+	}
+
+	return info.dli_fbase;
+}
+
+static int initialize_file_contents(void)
+{
+	int fd, page_sz = sysconf(_SC_PAGESIZE);
+	ssize_t n = 0, cur, off;
+	void *addr;
+
+	fd = open("/proc/self/exe", O_RDONLY);
+	if (!ASSERT_OK_FD(fd, "Open /proc/self/exe\n"))
+		return 1;
+
+	do {
+		cur = read(fd, file_contents + n, sizeof(file_contents) - n);
+		if (!ASSERT_GT(cur, 0, "read success"))
+			break;
+		n += cur;
+	} while (n < sizeof(file_contents));
+
+	close(fd);
+
+	if (!ASSERT_EQ(n, sizeof(file_contents), "Read /proc/self/exe\n"))
+		return 1;
+
+	addr = get_executable_base_addr();
+	if (!ASSERT_NEQ(addr, NULL, "get executable address"))
+		return 1;
+
+	/* page-align base file address */
+	addr = (void *)((unsigned long)addr & ~(page_sz - 1));
+
+	for (off = 0; off < sizeof(file_contents); off += page_sz) {
+		if (!ASSERT_OK(madvise(addr + off, page_sz, MADV_PAGEOUT),
+			       "madvise pageout"))
+			return errno;
+	}
+
+	return 0;
+}
+
+static void run_test(const char *prog_name)
+{
+	struct file_reader *skel;
+	struct bpf_program *prog;
+	int err, fd;
+
+	err = initialize_file_contents();
+	if (!ASSERT_OK(err, "initialize file contents"))
+		return;
+
+	skel = file_reader__open();
+	if (!ASSERT_OK_PTR(skel, "file_reader__open"))
+		return;
+
+	bpf_object__for_each_program(prog, skel->obj) {
+		bpf_program__set_autoload(prog, strcmp(bpf_program__name(prog), prog_name) == 0);
+	}
+
+	memcpy(skel->bss->user_buf, file_contents, sizeof(file_contents));
+	skel->bss->pid = getpid();
+
+	err = file_reader__load(skel);
+	if (!ASSERT_OK(err, "file_reader__load"))
+		goto cleanup;
+
+	err = file_reader__attach(skel);
+	if (!ASSERT_OK(err, "file_reader__attach"))
+		goto cleanup;
+
+	fd = open("/proc/self/exe", O_RDONLY);
+	if (fd >= 0)
+		close(fd);
+
+	ASSERT_EQ(skel->bss->err, 0, "err");
+	ASSERT_EQ(skel->bss->run_success, 1, "run_success");
+cleanup:
+	file_reader__destroy(skel);
+}
+
+void test_file_reader(void)
+{
+	if (test__start_subtest("on_open_expect_fault"))
+		run_test("on_open_expect_fault");
+
+	if (test__start_subtest("on_open_validate_file_read"))
+		run_test("on_open_validate_file_read");
+
+	if (test__start_subtest("negative"))
+		RUN_TESTS(file_reader_fail);
+}