allocate a Cdb struct rather than using a single static one, note that cdb_free does _not_ call alloc_free, just releases the map, in fact alloc_free is not called anywhere!

#include "buffer.h"

void buffer_init(buffer *s,ssize_t (*op)(),int fd,char *buf,unsigned int len)
{
  s->x = buf;
  s->fd = fd;
  s->op = op;
  s->p = 0;
  s->n = len;
}