Sample code for handling _IO_READ messages in pread*()

The following sample code demonstrates how to handle _IO_READ for the case where the client calls one of the pread*() functions.

/* we are defining io_pread_t here to make the code below simple */
typedef struct {
    struct _io_read         read;
    struct _xtype_offset    offset;
} io_pread_t;

int io_read (resmgr_context_t *ctp, io_read_t *msg, RESMGR_OCB_T *ocb)
{
    off64_t offset; /* where to read from */
    int     status;

    if ((status = iofunc_read_verify(ctp, msg, ocb, NULL)) != EOK) {
        return(status);
    }
    
    switch(msg->i.xtype & _IO_XTYPE_MASK) {
    case _IO_XTYPE_NONE:
        offset = ocb->offset;
        break;
    case _IO_XTYPE_OFFSET:
        /*
         *  io_pread_t is defined above.
         *  Client is doing a one-shot read to this offset by
         *  calling one of the pread*() functions
         */
        offset = ((io_pread_t *) msg)->offset.offset;
        break;
    default:
        return(ENOSYS);
    }
    ...
}