Linux内存映射函数mmap与匿名内存块

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/termios.h>
#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>

#include <fcntl.h>
#include <sys/mman.h>

#define COPYINCR (1024 * 1024 * 1024) /* 1 GB */

int main(int argc, char *argv[])
{
	int fdin, fdout;
	void *src;
	void *dst;
	size_t copysz;
	struct stat sbuf;
	off_t fsz = 0;

	if (argc != 3)
	{
		printf("usage: %s <fromfile> <tofile>\n", argv[0]);
		exit(1);
	}

	if ((fdin = open(argv[1], O_RDONLY)) < 0)
	{
		printf("can't open %s for reading\n", argv[1]);
	}

	if ((fdout = open(argv[2], O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)) < 0)
	{
		printf("can't creat %s for writing\n", argv[2]);
	}

	if (fstat(fdin, &sbuf) < 0) /* need size of input file */
	{
		printf("fstat error\n");
	}

	if (ftruncate(fdout, sbuf.st_size) < 0) /* set output file size */
	{
		printf("ftruncate error\n");
	}

	while (fsz < sbuf.st_size)
	{
		if ((sbuf.st_size - fsz) > COPYINCR)
		{
			copysz = COPYINCR;
		}
		else
		{
			copysz = sbuf.st_size - fsz;
		}

		if ((src = mmap(0, copysz, PROT_READ, MAP_SHARED, fdin, fsz)) == MAP_FAILED)
		{
			printf("mmap error for input\n");
		}
		printf("src: %p\n", (char *)src);
		if ((dst = mmap(0, copysz, PROT_READ | PROT_WRITE, MAP_SHARED, fdout, fsz)) == MAP_FAILED)
		{
			printf("mmap error for output\n");
		}
		printf("dst: %p\n", (char *)src);
		memcpy(dst, src, copysz); /* does the file copy */
		munmap(src, copysz);
		munmap(dst, copysz);
		fsz += copysz;
	}
	exit(0);
}

// gcc -o main1 -Wall -g -ggdb -O0 -g3 -gdwarf-2 main1.c

[mingjie@centos ~/proj/mmap]$ gcc -o main1 -Wall -g -ggdb -O0 -g3 -gdwarf-2 main1.c
[mingjie@centos ~/proj/mmap]$ ./main1 a.data b.data
src: 0x7fde70798000
dst: 0x7fde70798000
[mingjie@centos ~/proj/mmap]$ cat a.data 
aaaaaaaa
bbb
[mingjie@centos ~/proj/mmap]$ cat b.data 
aaaaaaaa
bbb

// 定义：
 void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset);


// 实例1中：
mmap(0, copysz, PROT_READ, MAP_SHARED, fdin, fsz)
mmap(0, copysz, PROT_READ | PROT_WRITE, MAP_SHARED, fdout, fsz)

CreateAnonymousSegment
  ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,  PG_MMAP_FLAGS | mmap_flags, -1, 0);

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
	/*Pointer to shared memory region*/
	int *addr;

	addr = mmap(NULL, sizeof(int), PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
	if (addr == MAP_FAILED)
	{
		fprintf(stderr, "mmap() failed\n");
		exit(EXIT_FAILURE);
	}

	*addr = 1;

	/*Parent and child share mapping*/
	switch (fork())
	{
	case -1:
		fprintf(stderr, "fork() failed\n");
		exit(EXIT_FAILURE);

	case 0:
		/*Child: increment shared integer and exit*/
		printf("Child started, value = %d, ++value\n", *addr);
		(*addr)++;

		if (munmap(addr, sizeof(int)) == -1)
		{
			fprintf(stderr, "munmap()() failed\n");
			exit(EXIT_FAILURE);
		}
		exit(EXIT_SUCCESS);

	default:
		/*Parent: wait for child to terminate*/
		if (wait(NULL) == -1)
		{
			fprintf(stderr, "wait() failed\n");
			exit(EXIT_FAILURE);
		}

		printf("In parent, value = %d\n", *addr);
		if (munmap(addr, sizeof(int)) == -1)
		{
			fprintf(stderr, "munmap()() failed\n");
			exit(EXIT_FAILURE);
		}
		exit(EXIT_SUCCESS);
	}
}

// gcc -o main3 -Wall -g -ggdb -O0 -g3 -gdwarf-2 main3.c

[mingjie@centos ~/proj/mmap]$ ./main3
Child started, value = 1, ++value
In parent, value = 2