banan-os/userspace/mmap-shared-test/main.cpp

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#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;
}