Re: [PATCH v2 1/2][4.15] tools/x86: don't rebuild cpuid-autogen.h every time

From: Ian Jackson <iwj@xenproject.org>
To: Jan Beulich <jbeulich@suse.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	"Ian Jackson" <iwj@xenproject.org>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH v2 1/2][4.15] tools/x86: don't rebuild cpuid-autogen.h every time
Date: Fri, 12 Mar 2021 10:22:03 +0000	[thread overview]
Message-ID: <24651.16587.79927.894745@mariner.uk.xensource.com> (raw)
In-Reply-To: <1b8aee19-9194-153c-8dbb-0aec3412e255@suse.com>

Jan Beulich writes ("[PATCH v2 1/2][4.15] tools/x86: don't rebuild cpuid-autogen.h every time"):
> Ian did suggest to pass -0r to xargs (and -print0 to find), but I
> couldn't convince myself that these are standard compliant options. We
> don't use any special characters in file names, so -print0 / -0
> shouldn't be necessary at all. The stray rm invocation when there is no
> output from find can be taken care of by passing -f to it.

I addressed these portability questions in my original mail.

I said that I had checked FreeBSD find and xargs have all these
options.  I didn't check the other *BSDs but I see no reason to think
they would be different.

find -print0 and xargs -0 are not in SuS (for bad reasons) but these
are obviously necessary (unless one thinks people are supposed to use
  -exec printf "%s\n" '{}' \;
when the output is going to something more complicated an just some
command's arguments.

IOW we are IMO find to rely on both these options.

I would be OK with find -exec + in this case.  The {} must be quoted.

> --- a/tools/include/Makefile
> +++ b/tools/include/Makefile
> @@ -19,7 +19,7 @@ xen-foreign:
>  	$(MAKE) -C xen-foreign
>  
>  xen-dir:
> -	@rm -rf xen acpi
> +	find xen/ acpi/ -type l 2>/dev/null | xargs rm -f --

I disapprove of the 2>/dev/null and the -f because I disapprove of
suppressing.

Ian.