Re: [XEN PATCH v6 20/31] build: generate "include/xen/compile.h" with filechk

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Thu, Aug 05, 2021 at 09:20:10AM +0200, Jan Beulich wrote:
> On 01.07.2021 16:10, Anthony PERARD wrote:
> > This will always try regenerate the content of compile.h, but if it
> > didn't change the file isn't updated.
> > 
> > Also, as it's currently the case, the file isn't regenerated during
> > `sudo make install` if it exist and does belong to a different user.
> > 
> > Thus, we can remove the target "delete-unfresh-files".
> > Target $(TARGET) still need a phony dependency, so add FORCE.
> > 
> > This patch imports the macro 'filechk' from Linux v5.12.
> 
> Would you mind clarifying why $(if_changed ...) cannot be used here
> (unlike for .banner in the earlier patch)?

if_changed can be used instead of filechk. I probably use "filechk"
because I was looking for an excuse to use it, so I've used it here.

filechk advantage over if_changed is that the output of the command is
compared so there is no need to have an extra dependency (.*.cmd) file
generated. That probably mostly an advantage when the generated file
changed often, or when the command is simple enough.

But it seems that "filechk" is only used once in this patch series, in
this patch. So I can rework the patch to use "if_changed" instead, that
would avoid the need to import another macro from Linux, and avoid the
weird need to have the command "cat" the target when update isn't
wanted.

Thanks,

-- 
Anthony PERARD