Re: [PATCH v2 2/4] python/qemu: accel: Add list_accel() method

[Cleber Rosa <crosa@redhat.com>]

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On Wed, Dec 11, 2019 at 02:58:35PM -0200, Wainer dos Santos Moschetta wrote:
> 
> On 12/9/19 10:52 PM, Cleber Rosa wrote:
> > On Fri, Dec 06, 2019 at 04:34:31PM -0500, Wainer dos Santos Moschetta wrote:
> > > Since commit cbe6d6365a48 the command `qemu -accel help` returns
> > > the list of accelerators enabled in the QEMU binary. This adds
> > > the list_accel() method which return that same list.
> > > 
> > > Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
> > > Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
> > > Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> > > ---
> > >   python/qemu/accel.py | 23 +++++++++++++++++++++++
> > >   1 file changed, 23 insertions(+)
> > > 
> > > diff --git a/python/qemu/accel.py b/python/qemu/accel.py
> > > index cbeac10dd1..746b7e68f5 100644
> > > --- a/python/qemu/accel.py
> > > +++ b/python/qemu/accel.py
> > > @@ -14,7 +14,11 @@ accelerators.
> > >   # the COPYING file in the top-level directory.
> > >   #
> > > +import logging
> > >   import os
> > > +import subprocess
> > > +
> > > +LOG = logging.getLogger(__name__)
> > >   # Mapping host architecture to any additional architectures it can
> > >   # support which often includes its 32 bit cousin.
> > > @@ -23,6 +27,25 @@ ADDITIONAL_ARCHES = {
> > >       "aarch64" : "armhf"
> > >   }
> > > +def list_accel(qemu_bin):
> > > +    """
> > > +    List accelerators enabled in the QEMU binary.
> > > +
> > > +    @param qemu_bin (str): path to the QEMU binary.
> > > +    @raise Exception: if failed to run `qemu -accel help`
> > > +    @return a list of accelerator names.
> > > +    """
> > > +    if not qemu_bin:
> > > +        return []
> > > +    try:
> > > +        out = subprocess.check_output("%s -accel help" % qemu_bin, shell=True)
> > There's no need to use a shell here.  This could become:
> > 
> >     out = subprocess.check_output([qemu_bin, '-accel' 'help'])
> 
> Ack
> 
> > 
> > > +    except:
> > > +        LOG.debug("Failed to get the list of accelerators in %s" % qemu_bin)
> > > +        raise
> > > +    lines = out.decode().splitlines()
> > And maybe discard the first line earlier with:
> > 
> >     lines = out.decode().splitlines()[1:]
> > 
> > Also, you could avoid the manual decode() with the `universal_newlines`
> > option to subprocess.check_output(), ie:
> > 
> >     accels = subprocess.check_output([qemu-bin, '-accel', 'help'],
> >                                      universal_newlines=True).splitlines()[1:]
> 
> Nice. v3 will have universal_newlines=True.
> 
> > 
> > > +    # Skip the first line which is the header.
> > > +    return [l.strip() for l in lines[1:] if l]
> > > +
> > I think that the `if l` check can actually hide undesirable behavior
> > (bugs) in the `qemu -accel ?` output.  I don't remember seeing
> > `-$(option) ?` returning empty strings but doesn't mean it couldn't
> > and shouldn't).
> > 
> > I do remember `-machine ?` returning random non-printable characters
> > that turned out to be a bug, though.
> 
> Double-checking: are you suggesting to remove the 'if not empty' check so
> that bugs on output could emerge?
>

Yes, that's my suggestion.  I don't think we need to process QEMU's
output beyond what it's expected to be returned.

Cheers,
- Cleber.

> Thanks!
> 
> - Wainer
> 
> > 
> > >   def kvm_available(target_arch=None):
> > >       host_arch = os.uname()[4]
> > >       if target_arch and target_arch != host_arch:
> > > -- 
> > > 2.21.0
> > > 
> > - Cleber.
> 
> 

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