[bpf-next 2/4] selftests/bpf: add read_with_timeout() utility function

[Eduard Zingerman <eddyz87@gmail.com>]

int read_with_timeout(int fd, char *buf, size_t count, long usec)

As a regular read(2), but allows to specify a timeout in
micro-seconds. Returns -EAGAIN on timeout.
Implemented using select().

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
 tools/testing/selftests/bpf/Makefile     |  1 +
 tools/testing/selftests/bpf/io_helpers.c | 21 +++++++++++++++++++++
 tools/testing/selftests/bpf/io_helpers.h |  7 +++++++
 3 files changed, 29 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/io_helpers.c
 create mode 100644 tools/testing/selftests/bpf/io_helpers.h

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index edef5df08cb2..b1080284522d 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -742,6 +742,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c		\
 			 unpriv_helpers.c 	\
 			 netlink_helpers.c	\
 			 jit_disasm_helpers.c	\
+			 io_helpers.c		\
 			 test_loader.c		\
 			 xsk.c			\
 			 disasm.c		\
diff --git a/tools/testing/selftests/bpf/io_helpers.c b/tools/testing/selftests/bpf/io_helpers.c
new file mode 100644
index 000000000000..4ada0a74aa1f
--- /dev/null
+++ b/tools/testing/selftests/bpf/io_helpers.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <sys/select.h>
+#include <unistd.h>
+#include <errno.h>
+
+int read_with_timeout(int fd, char *buf, size_t count, long usec)
+{
+	const long M = 1000 * 1000;
+	struct timeval tv = { usec / M, usec % M };
+	fd_set fds;
+	int err;
+
+	FD_ZERO(&fds);
+	FD_SET(fd, &fds);
+	err = select(fd + 1, &fds, NULL, NULL, &tv);
+	if (err < 0)
+		return err;
+	if (FD_ISSET(fd, &fds))
+		return read(fd, buf, count);
+	return -EAGAIN;
+}
diff --git a/tools/testing/selftests/bpf/io_helpers.h b/tools/testing/selftests/bpf/io_helpers.h
new file mode 100644
index 000000000000..21e1134cd3ce
--- /dev/null
+++ b/tools/testing/selftests/bpf/io_helpers.h
@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <unistd.h>
+
+/* As a regular read(2), but allows to specify a timeout in micro-seconds.
+ * Returns -EAGAIN on timeout.
+ */
+int read_with_timeout(int fd, char *buf, size_t count, long usec);
-- 
2.47.0