mmap内存映射复习

c语言初学时，比较常见的一个习题就是实现cp。

使用c库实现的cp就不赘述了。

最近工作用到内存映射，就拿来练下手，复习一下mmap的用法。

很简单，将目标文件和源文件映射到内存，然后使用memcpy拷贝即可。

可以省去中间缓存的创建，代码页较为简单，拷贝速度也不错。

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>

#define COFYMODE 0666

int copy(const char* src, const char* dest)
{
    int ret = -1;
    int in_fd = -1, out_fd = -1;
    size_t filesize;
    char nullbyte;
    void *source_addr = NULL;
    void *dest_addr = NULL;

    /* check args */
    if(src == NULL || dest == NULL){
        fprintf(stderr,"file path can not be null
");
        return ret;
    }

    /* open files */
    if((in_fd=open(src, O_RDONLY))==-1) {
        fprintf(stderr, "Cannot open %s
", src);
        return ret;
    }


#if defined(i386) || defined(__x86_64) || defined(__x86_64__) || defined(i686)
    if((out_fd=open(dest, O_RDWR|O_CREAT|O_TRUNC,COFYMODE))==-1)
    {
        fprintf(stderr, "Cannot open %s
", dest);
        ret = -1;
        goto cleanup;
    }
#else
    if((out_fd=open(dest, O_WRONLY|O_CREAT|O_TRUNC,COFYMODE))==-1)
    {
        fprintf(stderr, "Cannot create %s
", dest);
        ret = -1;
        goto cleanup;
    }
#endif

   if((filesize=lseek(in_fd,0,SEEK_END))==-1)
   {
       fprintf(stderr, "Could not seek to end of file %s
", src);
        ret = -1;
        goto cleanup;
   }

   if(filesize == 0)
   {
       ret = 0;
       goto cleanup;
   }

    lseek(out_fd,filesize-1,SEEK_SET);
    write(out_fd,&nullbyte,1);

    /* setup the memory maps */
    if((source_addr=mmap(NULL,filesize,PROT_READ,MAP_SHARED,in_fd,0))==(void *)-1)
    {
        fprintf(stderr, "Error mapping file %s
", src);
        ret = -1;
        goto cleanup;
    }


    if((dest_addr=mmap(NULL,filesize,PROT_WRITE,MAP_SHARED,out_fd,0))==(void *)-1)
    {
        fprintf(stderr, "Error mapping file %s
", dest);
        ret = -1;
        goto cleanup;
    }

    /* copy the input to output by doing a memcpy */
    memcpy(dest_addr,source_addr,filesize);

cleanup:
    /*unmap the fiels */
    if(source_addr) munmap(source_addr,filesize);
    if(dest_addr) munmap(dest_addr,filesize);

    /* close the files */
    if(in_fd > 0)close(in_fd);
    if(out_fd > 0) close(out_fd);

    return ret;
}

int main(int argc, char* argv[])
{
    if(argc < 3)
    {
        fprintf(stderr, "useage: %s src_file dest_file", argv[0]);
        return -1;
    }

    return copy(argv[1], argv[2]);
}