[Libguestfs] [PATCH] lib: Pick up qemu-img path at build time.

[Richard W.M. Jones]

On Fri, Oct 06, 2017 at 04:50:44PM +0200, Pino Toscano wrote:
> On Friday, 6 October 2017 15:59:42 CEST Richard W.M. Jones wrote:
> > The main purpose of this change is two-fold:
> > 
> > (1) Ensure that we run the same version of qemu-img that we are
> > built against.
> > 
> > (2) Allow the qemu-img path to be overridden at build time in case
> > it's on a nonstandard path or (like RHV) has a nonstandard name.
> > ---
> 
> As I mentioned in other series, I am not a fan of hardcoding at build
> time paths used at runtime.  This patch has different issues:
> a) the hardcoding itself (which IMHO is a step backward)
> b) what the patch does just cover a very minimal set of all the
>    qemu-img invocations; all the tools rely on $PATH
> c) it is not overridable at all: since qemu can be changed in different
>    ways (API entry, envvar), it is not logic that qemu-img (built from
>    the same sources of qemu) cannot be changed at all; this situation
>    e.g. makes it not possible to use a custom qemu build (that says
>    enables some feature) in libguestfs
> d) the point (2) above implies supporting RHV would mean rebuilding
>    libguestfs just for that, which makes testing harder than needed
> 
> qemu is the "special flower" in this situation, since it can be outside
> of $PATH (hi RHEL), with a custom name, etc.  qemu-img does not have any
> of the qemu peculiarities.

This is all true, but unless we make qemu-img configurable at runtime
(which is extra complexity), I'm not sure what to do about it.

FWIW in RHEL qemu-img and qemu-img-rhev both ship /usr/bin/qemu-img.
(I previously thought that the binaries had different names, did that
change recently or was a I just mis-remembering??)

Rich.

-- 
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