Re: [Xen-devel] [PATCH 00 of 16 RFC] add libxl support for blktap3 and introduce the blktap3 build system

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-10-24 at 18:02 +0100, Thanos Makatos wrote:
> This series introduces support for blktap3 in libxl and adds the basis of the
> blktap3 build system. There is no essential blktap3 functionality yet: all
> blktap3 functions are stubs and they will be implemented in later patches. 
> This
> means that trying to use tap as the disk backend for a guest will make libxl
> complain since all of blktap3 functions return a failure error code. Most
> header files introduced in this series require some basic documentation.
> Finally, licenses need to be verified.

As it stands this series will break the build and/or xl functionality at
various points. I recommend ordering them as:
      * Stage 1: populate tools/blktap3, make it build with make -C
        tools/blktap3 (build breakage within tools/blktap3 doesn't
        matter during this stage)
      * Stage 2: connect tools/blktap3 to the top-level build system,
        but don't use it anywhere yet. At this point tools/blktap3 must
        compile successfully.
      * Third tranche: Patch libxl/xl etc to make them use blktap3
        instead of blktap2.

I'm also not convinced this pattern of adding dummy functions up front
and then switching them in with real implementations later is necessary
here. Sometimes that can be a useful technique for avoiding bisection
breakage but it doesn't seem like it should be needed if you follow
something like the staging proposal above.

I'm going to take a pass through the patches but I won't comment on
anything arising from either of the above.

Ian.


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