Re: [RFC PATCH] Fix usage of stdatomic.h for C++ compilers

[Bart Van Assche <bvanassche@acm.org>]

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On 2020-06-27 08:39, Hrvoje Zeba wrote:
> Any suggestions?

How about the two attached (untested) patches?

Thanks,

Bart.



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From 2d6b8423ece7f00798d73ede08719d4da6abbd46 Mon Sep 17 00:00:00 2001
From: Bart Van Assche <bvanassche@acm.org>
Date: Sat, 27 Jun 2020 08:40:23 -0700
Subject: [PATCH liburing 1/2] Make the liburing header files again compatible
 with C++

This patch has been tested by inspecting the output of the following
command:

g++ -I src/include -c -Wall -Wextra src/*.c

Fixes: b9c0bf79aa87 ("src/include/liburing/barrier.h: Use C11 atomics") # .
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 src/include/liburing.h         |  8 ++++----
 src/include/liburing/barrier.h | 37 ++++++++++++++++++++++++++++++++--
 2 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/src/include/liburing.h b/src/include/liburing.h
index c9034fc0df1b..76e2b854f957 100644
--- a/src/include/liburing.h
+++ b/src/include/liburing.h
@@ -2,10 +2,6 @@
 #ifndef LIB_URING_H
 #define LIB_URING_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <sys/socket.h>
 #include <sys/uio.h>
 #include <sys/stat.h>
@@ -19,6 +15,10 @@ extern "C" {
 #include "liburing/io_uring.h"
 #include "liburing/barrier.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /*
  * Library interface to io_uring
  */
diff --git a/src/include/liburing/barrier.h b/src/include/liburing/barrier.h
index c8aa4210371c..5ad337f33262 100644
--- a/src/include/liburing/barrier.h
+++ b/src/include/liburing/barrier.h
@@ -2,8 +2,6 @@
 #ifndef LIBURING_BARRIER_H
 #define LIBURING_BARRIER_H
 
-#include <stdatomic.h>
-
 /*
 From the kernel documentation file refcount-vs-atomic.rst:
 
@@ -23,6 +21,40 @@ after the acquire operation executes. This is implemented using
 :c:func:`smp_acquire__after_ctrl_dep`.
 */
 
+#ifdef __cplusplus
+#include <atomic>
+
+template <typename T>
+static inline void IO_URING_WRITE_ONCE(T &var, T val)
+{
+	std::atomic_store_explicit(reinterpret_cast<std::atomic<T> *>(&var),
+				   val, std::memory_order_relaxed);
+}
+template <typename T>
+static inline T IO_URING_READ_ONCE(const T &var)
+{
+	return std::atomic_load_explicit(
+		reinterpret_cast<const std::atomic<T> *>(&var),
+		std::memory_order_relaxed);
+}
+
+template <typename T>
+static inline void io_uring_smp_store_release(T *p, T v)
+{
+	std::atomic_store_explicit(reinterpret_cast<std::atomic<T> *>(p), v,
+				   std::memory_order_release);
+}
+
+template <typename T>
+static inline T io_uring_smp_load_acquire(const T *p)
+{
+	return std::atomic_load_explicit(
+		reinterpret_cast<const std::atomic<T> *>(p),
+		std::memory_order_acquire);
+}
+#else
+#include <stdatomic.h>
+
 #define IO_URING_WRITE_ONCE(var, val)				\
 	atomic_store_explicit(&(var), (val), memory_order_relaxed)
 #define IO_URING_READ_ONCE(var)					\
@@ -32,5 +64,6 @@ after the acquire operation executes. This is implemented using
 	atomic_store_explicit((p), (v), memory_order_release)
 #define io_uring_smp_load_acquire(p)				\
 	atomic_load_explicit((p), memory_order_acquire)
+#endif
 
 #endif /* defined(LIBURING_BARRIER_H) */

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From 0b896d7bf992caadde8f0c4d57478800b2261507 Mon Sep 17 00:00:00 2001
From: Bart Van Assche <bvanassche@acm.org>
Date: Sat, 27 Jun 2020 09:09:59 -0700
Subject: [PATCH liburing 2/2] Add a C++ unit test

Since the liburing header files support C++ compilers, add a C++ unit test.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 test/Makefile       |  9 +++++++--
 test/sq-full-cpp.cc | 45 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 2 deletions(-)
 create mode 100644 test/sq-full-cpp.cc

diff --git a/test/Makefile b/test/Makefile
index e103296fabdd..8b81d2d5f67c 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -10,7 +10,8 @@ override CFLAGS += -Wall -Wextra -Wno-unused-parameter -Wno-sign-compare\
 	-I../src/include/ -include ../config-host.h
 
 all_targets += poll poll-cancel ring-leak fsync io_uring_setup io_uring_register \
-	       io_uring_enter nop sq-full cq-full 35fa71a030ca-test \
+	       io_uring_enter nop sq-full sq-full-cpp cq-full \
+		35fa71a030ca-test \
 		917257daa0fe-test b19062a56726-test eeed8b54e0df-test link \
 		send_recvmsg a4c0b3decb33-test 500f9fbadef8-test timeout \
 		sq-space_left stdout cq-ready cq-peek-batch file-register \
@@ -41,8 +42,12 @@ all: $(all_targets)
 %: %.c
 	$(QUIET_CC)$(CC) $(CFLAGS) -o $@ $< -luring $(XCFLAGS)
 
+%: %.cc
+	$(QUIET_CC)$(CXX) $(CFLAGS) -o $@ $< -luring $(XCFLAGS)
+
 test_srcs := poll.c poll-cancel.c ring-leak.c fsync.c io_uring_setup.c \
-	io_uring_register.c io_uring_enter.c nop.c sq-full.c cq-full.c \
+	io_uring_register.c io_uring_enter.c nop.c sq-full.c sq-full-cpp.cc \
+	cq-full.c \
 	35fa71a030ca-test.c 917257daa0fe-test.c b19062a56726-test.c \
 	eeed8b54e0df-test.c link.c send_recvmsg.c a4c0b3decb33-test.c \
 	500f9fbadef8-test.c timeout.c sq-space_left.c stdout.c cq-ready.c\
diff --git a/test/sq-full-cpp.cc b/test/sq-full-cpp.cc
new file mode 100644
index 000000000000..ba400996e615
--- /dev/null
+++ b/test/sq-full-cpp.cc
@@ -0,0 +1,45 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Description: test SQ queue full condition
+ *
+ */
+#include <errno.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+
+#include "liburing.h"
+
+int main(int argc, char *argv[])
+{
+	struct io_uring_sqe *sqe;
+	struct io_uring ring;
+	int ret, i;
+
+	if (argc > 1)
+		return 0;
+
+	ret = io_uring_queue_init(8, &ring, 0);
+	if (ret) {
+		fprintf(stderr, "ring setup failed: %d\n", ret);
+		return 1;
+
+	}
+
+	i = 0;
+	while ((sqe = io_uring_get_sqe(&ring)) != NULL)
+		i++;
+
+	if (i != 8) {
+		fprintf(stderr, "Got %d SQEs, wanted 8\n", i);
+		goto err;
+	}
+
+	io_uring_queue_exit(&ring);
+	return 0;
+err:
+	io_uring_queue_exit(&ring);
+	return 1;
+}