#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <strings.h>

extern const char *__progname;

static int cfd;
static int ffd;
static int ro;

static void usage(void)
{
 fprintf(stderr,"Usage: %s pseudo-disk-device backing-file\n",__progname);
 exit(1);
}

static int dfdr(void *data, int len)
{
 char *dp;
 int n;

 dp = data;
 while (len > 0)
  { n = read(cfd,dp,len);
    if (n <= 0) return(1);
    dp += n;
    len -= n;
  }
 return(0);
}

int main(int, char **);
int main(int ac, char **av)
{
 unsigned char opc;

 if (ac != 3) usage();
 cfd = open(av[1],O_RDWR,0);
 if (cfd < 0)
  { fprintf(stderr,"%s: %s: %s\n",__progname,av[1],strerror(errno));
    exit(1);
  }
 ro = 0;
 ffd = open(av[2],O_RDWR,0);
 if (ffd < 0)
  { ro = 1;
    ffd = open(av[2],O_RDONLY,0);
    if (ffd < 0)
     { fprintf(stderr,"%s: %s: %s\n",__progname,av[2],strerror(errno));
       exit(1);
     }
  }
 while (1)
  { if (dfdr(&opc,1)) exit(0);
    switch (opc)
     { case 'o':
	   { unsigned char args[2];
	     int err;
	     if (dfdr(&args[0],2))
	      { fprintf(stderr,"%s: can't read open rwflag/part\n",__progname);
		exit(1);
	      }
	     switch (args[0])
	      { case 'r':
		   err = 0;
		   break;
		case 'w': case 'b':
		   err = ro ? EROFS : 0;
		   break;
		default:
		   fprintf(stderr,"%s: protocol error: invalid open flag 0x%02x\n",__progname,args[0]);
		   exit(1);
		   break;
	      }
	     write(cfd,&err,sizeof(int));
	   }
	  break;
       case 'c':
	  break;
       case 'r':
	   { unsigned int blkno;
	     char buf[512];
	     int n;
	     if (dfdr(&blkno,sizeof(unsigned int)))
	      { fprintf(stderr,"%s: can't get read sector #\n",__progname);
		exit(1);
	      }
	     n = pread(ffd,&buf[0],512,blkno*(off_t)512);
		  if (n < 0)    n = errno;
	     else if (n != 512) n = EIO;
	     else               n = 0;
	     write(cfd,&n,sizeof(int));
	     write(cfd,&buf[0],512);
	   }
	  break;
       case 'w':
	   { char buf[512];
	     unsigned int blkno;
	     int n;
	     if ( dfdr(&blkno,sizeof(unsigned int)) ||
		  dfdr(&buf[0],512) )
	      { fprintf(stderr,"%s: can't read write packet\n",__progname);
		exit(1);
	      }
	     n = pwrite(ffd,&buf[0],512,blkno*(off_t)512);
		  if (n < 0)    n = errno;
	     else if (n != 512) n = EIO;
	     else               n = 0;
	     write(cfd,&n,sizeof(int));
	   }
	  break;
       case 'z':
	   { unsigned int l;
	     unsigned int h;
	     unsigned int m;
	     static int ok(unsigned int b)
	      { char junk[512];
		return(pread(ffd,&junk[0],512,b*(off_t)512)==512);
	      }
	     l = 0;
	     h = 1;
	     while (ok(l))
	      { l = h;
		h <<= 1;
	      }
	     while (h-l > 1)
	      { m = (h + l) >> 1;
		if (ok(m)) l = m; else h = m;
	      }
	     write(cfd,&h,sizeof(int));
	   }
	  break;
       default:
	  fprintf(stderr,"%s: protocol error: invalid command 0x%02x\n",__progname,opc);
	  exit(1);
	  break;
     }
  }
}