[pve-devel] [PATCH v3 qemu 02/12] Write understood CPU flags into static file

[Thomas Lamprecht]

On 10/15/19 4:12 PM, Stefan Reiter wrote:
> located at /usr/share/kvm/cpu-flags-understood-$arch
> 
> This file can be read by qemu-server's "query_understood_cpu_flags"
> function, avoiding a more expensive call to QEMU.
> 
> For now, only x86_64 is implemented, since aarch64 doesn't print any flags when
> called this way.
> 
> Signed-off-by: Stefan Reiter <s.reiter at proxmox.com>
> ---
> 
> v5: check for empty file
> 
>  debian/rules | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/debian/rules b/debian/rules
> index 8f428c7..bc43ade 100755
> --- a/debian/rules
> +++ b/debian/rules
> @@ -21,6 +21,8 @@ ARCH ?= $(shell dpkg-architecture -qDEB_HOST_GNU_CPU)
>  PACKAGE=pve-qemu-kvm
>  destdir := $(CURDIR)/debian/$(PACKAGE)
>  
> +flagfile := $(destdir)/usr/share/kvm/cpu-flags-understood-x86_64
> +
>  CFLAGS = -Wall
>  
>  ifneq (,$(findstring noopt,$(DEB_BUILD_OPTIONS)))
> @@ -128,6 +130,18 @@ install: build
>  	rm -Rf $(destdir)/usr/include
>  	rm -Rf $(destdir)/usr/lib*
>  
> +	# write files for understood CPU flags, since these are static for every
> +	# version (saves a QEMU call in qemu-server at runtime)
> +	$(destdir)/usr/bin/qemu-system-x86_64 -cpu help \
> +		| perl -0777 -pe ' \
> +			s/^.*Recognized CPUID flags://s; # remove up to flags \
> +			s/\n{2,}.*$$//s; # remove any trailing text \
> +			s/\s{2,}|\n/\s/g; # remove unnecessary whitespace \

yeah, replacing with \s won't magically use the whitespace detected before
but writes an actual s ;) so this is broken.

But actually I'd like a bit of a different approach, in doing this and
saving this.

First, I would prefer a newline separated list, this makes it much easier
to spot what differs between updates, e.g., with diffoscope.

Secondly, a debian/ hosted perl script would be preferred, e.g., something
like debian/parse-cpu-flags.pl:
----8<----
#!/usr/bin/perl

use warnings;
use strict;

my @flags = ();
my $got_flags_section;

while (<STDIN>) {
    if (/^\s*Recognized CPUID flags:/) {
        $got_flags_section = 1;
        next;
    }
    next if !$got_flags_section;

    s/^\s+//;

    push @flags, split(/\s+/);
}

print join("\n", @flags) or die "$!\n";
---->8----

you could move the "assert there flags at all" check there too, then a
simple:
$(destdir)/usr/bin/qemu-system-x86_64 -cpu help | ./debian/parse-cpu-flags.pl > $(flagfile)
would be enough in debian rules.

this would let us allow to keep the qemu-server patch as is. As you use
`split /\s+/` there, it still matches.

if you agree this can be send outside of this series revision, or done
by me, whatever you prefer.

> +		' > $(flagfile)
> +
> +	# check that file is not empty
> +	[ -s $(flagfile) ]
> +
>  # Build architecture-independent files here.
>  binary-indep: build install
>  # We have nothing to do by default.
>