linux ] O_DIRECT를 이용한 write / read 질문있습니다.

88 void main(void){
     89 
     90 char szFilename[]={"SMART.txt\0\0"};
     91 unsigned char abPacket[]={0x2A, 0x53,0x43,0x5F,0x49,0x4F,0x5F};
     93 int hDevice=0, a, b;
     94 unsigned char *buf= NULL;
     95 
     96 //buf = memalign(getpagesize(), getpagesize());
     97 //buf=(char*)valloc(4096);
     98 //b= posix_memalign(&buf, getpagesize(), getpagesize());
     99 //printf("buf: %08x\n", b);
    100 //perror("posiz_memalign error");
    101 //buf = malloc(strlen(abPacket)+getpagesize());
    102 //buf = buf&~0xFFF;
    103 
    104 posix_memalign((void**)&buf, getpagesize(), getpagesize());
    105 
    106 if(buf == NULL) {
    107         printf("malloc error\n");
    108         perror("posix_memalign error");
    109         return;
    110 }
    111 
    112 hDevice = open(szFilename, O_RDWR|O_DIRECT|O_CREAT|O_TRUNC, S_IRWXU);
    113 perror("open error");
    114 if (hDevice <0){
    115         printf("open error\n");
    116         return;
    117         }
    118 
    119 lseek(hDevice, getpagesize(), 0);
    120 perror("lseek error");
    121 memcpy(buf, abPacket, sizeof(abPacket));
    122 perror("memcpy error");
    123 printf("buf:%s\n",buf);
    124 //a = write(hDevice, buf, sizeof(abPacket)+getpagesize());
    125 a = write(hDevice, buf, getpagesize());
    126 if(a<0) {
    127 //      printf("write error: %08x\n", a);
    128         close(hDevice);
    129         free(buf);
    130         remove(szFilename);
    131         perror("write error");
    132         return;
    133         }
 
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