Clarifications

• You need to open the virtual disk file in sfs_format () function as well. At the end of the function you need to close it. The format function will initialize the on disk structures of the file system.
• You can use memcpy() or bcopy() to copy n bytes from one location to another one in program memory.
• You can use type-casting to put/access a structured data in a buffer (character array) like the following.

      struct foo {
          int a;
          int b;
          int c;
      };
      
      struct foo * p;
      
      char buf[100];
      
      p = (struct foo *) buf;
      
      p->a = 10 ;
      p->b = 20;
      p->c = 30;