[PATCH bpf-next v3 08/10] selftests/bpf: Test partial reads for io_uring, epoll iterators

[Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>]

Ensure that the output is consistent in face of partial reads that
return to userspace and then resume again later. To this end, we do
reads in 1-byte chunks, which is a bit stupid in real life, but works
well to simulate interrupted iteration. This also tests case where
seq_file buffer is consumed (after seq_printf) on interrupted read
before iterator invoked BPF prog again.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
---
 .../selftests/bpf/prog_tests/bpf_iter.c       | 33 ++++++++++++-------
 1 file changed, 22 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index cc0555c5b373..3a07fdf31874 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
@@ -73,13 +73,13 @@ static void do_dummy_read(struct bpf_program *prog)
 	bpf_link__destroy(link);
 }
 
-static int read_fd_into_buffer(int fd, char *buf, int size)
+static int __read_fd_into_buffer(int fd, char *buf, int size, size_t chunks)
 {
 	int bufleft = size;
 	int len;
 
 	do {
-		len = read(fd, buf, bufleft);
+		len = read(fd, buf, chunks ?: bufleft);
 		if (len > 0) {
 			buf += len;
 			bufleft -= len;
@@ -89,6 +89,11 @@ static int read_fd_into_buffer(int fd, char *buf, int size)
 	return len < 0 ? len : size - bufleft;
 }
 
+static int read_fd_into_buffer(int fd, char *buf, int size)
+{
+	return __read_fd_into_buffer(fd, buf, size, 0);
+}
+
 static void test_ipv6_route(void)
 {
 	struct bpf_iter_ipv6_route *skel;
@@ -1301,7 +1306,7 @@ static int io_uring_inode_match(int link_fd, int io_uring_fd)
 	return 0;
 }
 
-void test_io_uring_buf(void)
+void test_io_uring_buf(bool partial)
 {
 	DECLARE_LIBBPF_OPTS(bpf_iter_attach_opts, opts);
 	char rbuf[4096], buf[4096] = "B\n";
@@ -1375,7 +1380,7 @@ void test_io_uring_buf(void)
 	if (!ASSERT_GE(iter_fd, 0, "bpf_iter_create"))
 		goto end_close_fd;
 
-	ret = read_fd_into_buffer(iter_fd, rbuf, sizeof(rbuf));
+	ret = __read_fd_into_buffer(iter_fd, rbuf, sizeof(rbuf), partial);
 	if (!ASSERT_GT(ret, 0, "read_fd_into_buffer"))
 		goto end_close_iter;
 
@@ -1396,7 +1401,7 @@ void test_io_uring_buf(void)
 	bpf_iter_io_uring__destroy(skel);
 }
 
-void test_io_uring_file(void)
+void test_io_uring_file(bool partial)
 {
 	int reg_files[] = { [0 ... 7] = -1 };
 	DECLARE_LIBBPF_OPTS(bpf_iter_attach_opts, opts);
@@ -1464,7 +1469,7 @@ void test_io_uring_file(void)
 	if (!ASSERT_OK(ret, "io_uring_register_files"))
 		goto end_iter_fd;
 
-	ret = read_fd_into_buffer(iter_fd, rbuf, sizeof(rbuf));
+	ret = __read_fd_into_buffer(iter_fd, rbuf, sizeof(rbuf), partial);
 	if (!ASSERT_GT(ret, 0, "read_fd_into_buffer(iterator_fd, buf)"))
 		goto end_iter_fd;
 
@@ -1488,7 +1493,7 @@ void test_io_uring_file(void)
 	bpf_iter_io_uring__destroy(skel);
 }
 
-void test_epoll(void)
+void test_epoll(bool partial)
 {
 	const char *fmt = "B\npipe:%d\nsocket:%d\npipe:%d\nsocket:%d\nE\n";
 	DECLARE_LIBBPF_OPTS(bpf_iter_attach_opts, opts);
@@ -1554,7 +1559,7 @@ void test_epoll(void)
 	if (!ASSERT_GE(ret, 0, "snprintf") || !ASSERT_LT(ret, sizeof(buf), "snprintf"))
 		goto end_iter_fd;
 
-	ret = read_fd_into_buffer(iter_fd, rbuf, sizeof(rbuf));
+	ret = __read_fd_into_buffer(iter_fd, rbuf, sizeof(rbuf), partial);
 	if (!ASSERT_GT(ret, 0, "read_fd_into_buffer"))
 		goto end_iter_fd;
 
@@ -1666,9 +1671,15 @@ void test_bpf_iter(void)
 	if (test__start_subtest("buf-neg-offset"))
 		test_buf_neg_offset();
 	if (test__start_subtest("io_uring_buf"))
-		test_io_uring_buf();
+		test_io_uring_buf(false);
 	if (test__start_subtest("io_uring_file"))
-		test_io_uring_file();
+		test_io_uring_file(false);
 	if (test__start_subtest("epoll"))
-		test_epoll();
+		test_epoll(false);
+	if (test__start_subtest("io_uring_buf-partial"))
+		test_io_uring_buf(true);
+	if (test__start_subtest("io_uring_file-partial"))
+		test_io_uring_file(true);
+	if (test__start_subtest("epoll-partial"))
+		test_epoll(true);
 }
-- 
2.34.1