Re: [PATCH COMMITTED] src: Fix NDEBUG compilation: avoid side-effects in assert

[Eric Blake]

On 2/27/20 6:54 AM, Eric Blake wrote:

> > > +++ b/src/ios.c
> > > @@ -220,12 +220,14 @@ void
> > >   ios_close (ios io)
> > >   {
> > >     struct ios *tmp;
> > > +  int r;
> > >
> > >     /* XXX: if not saved, ask before closing.  */
> > >
> > >     /* Close the device operated by the IO space.
> > >        XXX: handle errors.  */
> > > -  assert (io->dev_if->close (io->dev));
> > > +  r = io->dev_if->close (io->dev);
> > > +  assert (r);
>
> Another way to do this that does not use temporary variables that we'd 
> have to ifdef out under NDEBUG would be:
>
> if (! io->dev_if->close (io->dev))
>    assert (0);
>
> I can make that switch if you'd like (and undo the addition of all my 
> temporaries).

And independently of that offer, at this particular code site we DO need 
to fix the XXX comment; at least my patch to add an NBD io space can 
have a failed dev_if->close() call if the NBD server went AWOL in the 
meantime.  The actions of a failing server should not cause poke to die 
from an assertion, but instead inform the user about the potential data 
loss due to the failed close.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org