Re: [Xen-devel] [Patch v2 3/3] update libxl__device_disk_from_xs_be() to support blktap device

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Wen Congyang writes ("[Patch v2 3/3] update libxl__device_disk_from_xs_be() to 
support blktap device"):
> [stuff]

Thanks for your attention to the details of this rather neglected
area.

This patch seems related to 
  [RFC Patch v4 8/9] store correct format into tapdisk-params/params
from Mon, 22 Sep 2014 13:59:20 +0800.

Is that right ?  I confess I don't know exactly how all of the tapdisk
plumbing works, but I do expect it to be rather ... idiosyncratic.  Is
this patch (and the other one) for blktap1 or blktap2 ?

Is there is some kind of document I should be looking at explaining
how the relevant blktap's xenstore protocol works ?  I found
tools/blktap/README and tools/blktap2/README but they don't seem to
answer the question.

I think it will be difficult to review this patch without a clear
description of the intended design.  You seem to have done much of the
reverse-engineering necessary, so perhaps you could provide a sketch
of the relevant information with your patch - perhaps as a doc comment
somewhere in the code, provided in a pre-patch ?  Also, I would like
to understand more clearly how this functionality interacts with Wei
Liu's new approach to libxl domain configuration management.

I think I should avoid reviewing the concrete implementation until I
feel I understand what the patch ought to do.  Otherwise we risk
iterating to improve details when the overall approach isn't
necessarily right.

Thanks,
Ian.

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