Xen devel - May 2007 - How do we add more memory ops?

Hi,
 
    /*
     * To allow safe resume of do_memory_op() after preemption, we need
to know
     * at what point in the page list to resume. For this purpose I
steal the
     * high-order bits of the @cmd parameter, which are otherwise unused
and zero.
     */
    #define MEMOP_EXTENT_SHIFT 4 /* cmd[:4] == start_extent */
    #define MEMOP_CMD_MASK     ((1 << MEMOP_EXTENT_SHIFT) - 1)
 
Why not using another hypercall argument for this? 
Before I''m making any changes.. are there any limitations?
 
Thanks,
Guy.


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