Re: [PATCH v5 01/11] xen/arm: xc_domain_ioport_permission(..) not supported on ARM.

[Ian Jackson <iwj@xxxxxxxxxxxxxx>]

Bertrand Marquis writes ("Re: [PATCH v5 01/11] xen/arm: 
xc_domain_ioport_permission(..) not supported on ARM."):
> So there is no comment remaining on this patch ?

I have been following this thread.  I think I have a notion of why
this is needed but I'm not 100% clear on it.  The commit message says
this:

> ARM architecture does not implement I/O ports. Ignore this call on ARM
> to avoid the overhead of making a hypercall just for Xen to return
> -ENOSYS.

which implies it's a performance improvement.  But the change also
suppresses an error return, so this commit message is false.  I think
that the thread has concluded something different, but it should be
explained in the commit message.  The purpose of a commit message is
precisely to capture the kind of considerations and discussion that
occurred in this thread.

If the overall outcome implied by this patch is correct (as I *think*
the thread has concluded) then I don't think the #ifdefery is
appropriate.  This should be done with a new arch-specific function in
libxl_x86.c and libxl_arm.c.  I'm not sure precisely what that
function should be called, but maybe something like
  libxl_ioports_supported
?

I see that the fact that we avoid #ifdefs wasn't documented in
CODING_STYLE, so I have sent a patch to add that.  Sorry about that.

Thanks,
Ian.