userspace/CMakeLists.txt

@@ -10,6 +10,7 @@ set(USERSPACE_PROJECTS
 	id
 	init
 	ls
+	mmap-shared-test
 	poweroff
 	Shell
 	snake

userspace/mmap-shared-test/CMakeLists.txt

@@ -0,0 +1,17 @@
+cmake_minimum_required(VERSION 3.26)
+
+project(mmap-shared-test CXX)
+
+set(SOURCES
+	main.cpp
+)
+
+add_executable(mmap-shared-test ${SOURCES})
+target_compile_options(mmap-shared-test PUBLIC -O2 -g)
+target_link_libraries(mmap-shared-test PUBLIC libc)
+
+add_custom_target(mmap-shared-test-install
+	COMMAND sudo cp ${CMAKE_CURRENT_BINARY_DIR}/mmap-shared-test ${BANAN_BIN}/
+	DEPENDS mmap-shared-test
+	USES_TERMINAL
+)

userspace/mmap-shared-test/main.cpp

@@ -0,0 +1,115 @@
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#define FILE_NAME "test-file"
+#define FILE_SIZE (1024*1024)
+
+int prepare_file()
+{
+	int fd = open(FILE_NAME, O_RDWR | O_TRUNC | O_CREAT, 0666);
+	if (fd == -1)
+	{
+		perror("open");
+		return 1;
+	}
+
+	void* null_buffer = malloc(FILE_SIZE);
+	memset(null_buffer, 0x00, FILE_SIZE);
+
+	if (write(fd, null_buffer, FILE_SIZE) == -1)
+	{
+		perror("write");
+		return 1;
+	}
+
+	free(null_buffer);
+	close(fd);
+
+	printf("file created\n");
+
+	return 0;
+}
+
+int job1()
+{
+	int fd = open(FILE_NAME, O_RDONLY);
+	if (fd == -1)
+	{
+		perror("open");
+		return 1;
+	}
+
+	void* addr = mmap(nullptr, FILE_SIZE, PROT_READ, MAP_SHARED, fd, 0);
+	if (addr == MAP_FAILED)
+	{
+		perror("mmap");
+		return 1;
+	}
+
+	sleep(4);
+
+	size_t sum = 0;
+	for (int i = 0; i < FILE_SIZE; i++)
+		sum += ((uint8_t*)addr)[i];
+
+	munmap(addr, FILE_SIZE);
+	close(fd);
+
+	printf("sum: %zu\n", sum);
+
+	return 0;
+}
+
+int job2()
+{
+	sleep(2);
+
+	int fd = open(FILE_NAME, O_RDWR);
+	if (fd == -1)
+	{
+		perror("open");
+		return 1;
+	}
+
+	void* addr = mmap(nullptr, FILE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	if (addr == MAP_FAILED)
+	{
+		perror("mmap");
+		return 1;
+	}
+
+	memset(addr, 'a', FILE_SIZE);
+
+	munmap(addr, FILE_SIZE);
+	close(fd);
+
+	printf("expecting: %zu\n", (size_t)'a' * FILE_SIZE);
+
+	return 0;
+}
+
+int main()
+{
+	if (int ret = prepare_file())
+		return ret;
+
+	pid_t pid = fork();
+	if (pid == 0)
+		return job1();
+
+	if (pid == -1)
+	{
+		perror("fork");
+		return 1;
+	}
+
+	int ret = job2();
+	waitpid(pid, nullptr, 0);
+
+	return ret;
+}