Linuxオペレーティングシステムファイルキャッシュの解放

#define _FILE_OFFSET_BITS 64
#define __USE_XOPEN2K
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <getopt.h>

const struct option dcache_options[] = {
 {"sync",0,NULL,'s'},
 {"help",0,NULL,'h'},
 {NULL,0,NULL,0}
};

void usage(char* proc_name,int exit_code)
{
 printf("dcache is an utility to drop file cache.
"
 "usage:%s [-s] file
"
 "\t-s,--sync, sync data before drop cache.
"
 "\t-h,--help, print help.
",proc_name);
 exit(exit_code);
}

int dcache(int fd, int sync_data)
{
 off_t off,len;
 struct stat buf;
 int save_errno;
 save_errno = errno;

 if (sync_data) {
 if (fsync(fd) < 0) {
 printf("%s
",strerror(errno));
 errno = save_errno;
 return -1;
 }
 } 

 if (fstat(fd,&buf) < 0) {
 printf("%s
",strerror(errno)); 
 errno = save_errno;
 return -1;
 } 

 off = 0;
 len = buf.st_size;
 if (posix_fadvise(fd,off,len,POSIX_FADV_DONTNEED) < 0) {
 printf("%s
",strerror(errno)); 
 errno = save_errno;
 return -1;
 }

 return 0;
}

int main(int argc, char* argv[])
{
 int c,fd;
 char* file; 
 int long_index = 0;
 int print_help = 0; 
 int sync_data = 0;
 while ((c = getopt_long(argc,argv,"sh",dcache_options,&long_index)) != -1) {
 switch (c) {
 case 's':
 sync_data = 1;
 break;
 case 'h':
 print_help = 1;
 break;
 default:
 printf("unknown option -%c
",c); 
 usage(argv[0],EXIT_FAILURE);
 break;
 }
 }
 if (print_help) {
 usage(argv[0],EXIT_SUCCESS);
 }
 if (optind >= argc) {
 printf("file name required
"); 
 exit(EXIT_FAILURE);
 } 
 for (c = optind; c < argc; ++c) {
 file = argv[c];
 if ((fd = open(file,O_RDWR)) < 0) {
 printf("open %s failed.
",file); 
 } else {
 printf("drop cache of %s %s.
",file,dcache(fd,sync_data) == 0?"success":"failed");
 close(fd);
 }
 }
 exit(EXIT_SUCCESS);
}