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

[Wainer dos Santos Moschetta]

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 <address@hidden>
> > Reviewed-by: Alex Bennée <address@hidden>
> > Reviewed-by: Philippe Mathieu-Daudé <address@hidden>
> > ---
> >   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?

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.