我有一个程序,它是linux中复制程序的另一个变体(实际上,我在Mac OSX上)。为了支持复制大文件,我写了这样的内容:
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/mman.h>
#define BUFFSIZE 1024
int main(int argc, char **argv){
char *source, *destination;
int src_fd, dst_fd;
unsigned long long bytes_read;
size_t bytes;
struct timeval start, end;
int overall_time = 0;
unsigned long long offset = 0;
struct stat statbuf;
if(argc < 3){
printf("copy <source> <destination>\n");
exit(EXIT_FAILURE);
}
source = argv[1];
destination = argv[2];
src_fd = open(source, O_RDONLY, 0777);
if(src_fd < 0){
perror("src_fd");
exit(EXIT_FAILURE);
}
//bytes_read = lseek(src_fd, 0, SEEK_END);
fstat(src_fd, &statbuf);
bytes_read = statbuf.st_size;
dst_fd = open(destination, O_RDWR | O_CREAT, 0777);
if(dst_fd < 0){
perror("dst_fd");
exit(EXIT_FAILURE);
}
lseek(dst_fd, bytes_read -1, SEEK_SET);
write(dst_fd, "", 1);
gettimeofday(&start, NULL);
while(bytes_read > 0){
if(bytes_read < BUFFSIZE){
bytes = bytes_read;
bytes_read = 0;
}
else{
bytes = BUFFSIZE;
}
void *src_map = mmap(NULL, bytes, PROT_READ, MAP_SHARED, src_fd, (off_t)offset);
if(src_map == (void*) MAP_FAILED){
perror("src_map");
exit(EXIT_FAILURE);
}
void *dst_map = mmap(NULL, bytes, PROT_WRITE, MAP_SHARED, dst_fd, (off_t)offset);
if(dst_map == (void*) MAP_FAILED){
perror("dst_map");
exit(EXIT_FAILURE);
}
memcpy(dst_map, src_map, bytes);
int src_unmp = munmap(src_map, bytes);
if(src_unmp == -1){
perror("src_unmap");
exit(EXIT_FAILURE);
}
int dst_unmp = munmap(dst_map, bytes);
if(dst_unmp == -1){
perror("dst_unmap");
exit(EXIT_FAILURE);
}
offset += bytes;
bytes_read -= bytes;
}
gettimeofday(&end, NULL);
printf("overall = %d\n", (end.tv_usec - start.tv_usec));
close(src_fd);
close(dst_fd);
return 0;
}
在while语句中,程序尝试进行第一次迭代,并在尝试为mmap()
调用src_fd
时停留在第二次迭代中(第29行)。我希望程序可以正常运行,但在第二次迭代中会引发“ src_map:无效参数”错误。我个人认为是因为offset
。有人可以帮我吗?谢谢
是。问题出在偏移值上。偏移值应为页面大小的倍数。