swap_super.c

   1 #include <unistd.h>
   2 #include <stdlib.h>
   3 #include <fcntl.h>
   4 #include <stdio.h>
   5 #include <sys/mount.h>
   6 /*
   7  * This is a tiny test program to endian-swap
   8  * the superblock on a given device.
   9  * We simply read 4k from where the superblock should be
  10  * do the swap, and write it back
  11  * Don't use this on a real array, use mdadm.
  12  */
  13
  14 #define MD_RESERVED_BYTES               (64 * 1024)
  15 #define MD_RESERVED_SECTORS             (MD_RESERVED_BYTES / 512)
  16
  17 #define MD_NEW_SIZE_SECTORS(x)          ((x & ~(MD_RESERVED_SECTORS - 1)) - MD_RESERVED_SECTORS)
  18
  19 extern long long lseek64(int, long long, int);
  20
  21 int main(int argc, char *argv[])
  22 {
  23         int fd, i;
  24         unsigned long size;
  25         unsigned long long offset;
  26         char super[4096];
  27         if (argc != 2) {
  28                 fprintf(stderr, "Usage: swap_super device\n");
  29                 exit(1);
  30         }
  31         fd = open(argv[1], O_RDWR);
  32         if (fd<0) {
  33                 perror(argv[1]);
  34                 exit(1);
  35         }
  36         if (ioctl(fd, BLKGETSIZE, &size)) {
  37                 perror("BLKGETSIZE");
  38                 exit(1);
  39         }
  40         offset = MD_NEW_SIZE_SECTORS(size) * 512LL;
  41         if (lseek64(fd, offset, 0) < 0LL) {
  42                 perror("lseek64");
  43                 exit(1);
  44         }
  45         if (read(fd, super, 4096) != 4096) {
  46                 perror("read");
  47                 exit(1);
  48         }
  49
  50         for (i=0; i < 4096 ; i+=4) {
  51                 char t = super[i];
  52                 super[i] = super[i+3];
  53                 super[i+3] = t;
  54                 t=super[i+1];
  55                 super[i+1]=super[i+2];
  56                 super[i+2]=t;
  57         }
  58         /* swap the u64 events counters */
  59         for (i=0; i<4; i++) {
  60                 /* events_hi and events_lo */
  61                 char t=super[32*4+7*4 +i];
  62                 super[32*4+7*4 +i] = super[32*4+8*4 +i];
  63                 super[32*4+8*4 +i] = t;
  64
  65                 /* cp_events_hi and cp_events_lo */
  66                 t=super[32*4+9*4 +i];
  67                 super[32*4+9*4 +i] = super[32*4+10*4 +i];
  68                 super[32*4+10*4 +i] = t;
  69         }
  70
  71         if (lseek64(fd, offset, 0) < 0LL) {
  72                 perror("lseek64");
  73                 exit(1);
  74         }
  75         if (write(fd, super, 4096) != 4096) {
  76                 perror("write");
  77                 exit(1);
  78         }
  79         exit(0);
  80
  81 }