Handling readcond()

The same type of operation that was done to handle the pread()/_IO_XTYPE_OFFSET case can be used for handling the client's readcond() call:

typedef struct {
    struct _io_read        read;
    struct _xtype_readcond cond;
} io_readcond_t

Then:

struct _xtype_readcond *cond;
...
    CASE _IO_XTYPE_READCOND:
        cond = &((io_readcond_t *)msg)->cond;
        break;
}