[libvirt] [PATCH] qemu: Support chardevs with ARM virt machines

[Andrea Bolognani]

On Sat, 2017-06-24 at 16:07 +0200, Christoffer Dall wrote:
> > The way I see it, the bug is about libvirt being unable to
> > launch guests which use the <console><log> feature, and with
> > that in mind your patch is correct but doesn't solve the
> > issue, because even thought that specific error is gone you
> > immediately run into a different one and your guest is still
> > unable to start.
> 
> I didn't experience this, it was actually working on my end.  I wonder
> if it's related to the QEMU version, where I seem to remember we
> changed what some serial options turned into.  But I for sure did not
> see "-device isa-serial..." on the command line, so maybe not.

That's very different from the behavior I'm seeing, and I
can't figure out why that would be the case. That's why
having your QEMU command line would be very useful.

As for differences in QEMU binaries, there might be some
capability that I haven't considered and influences the
generated command line. I'll look into that.

> In any case, I'll reproduce again when I'm back and send you the details.

Sounds good to me.

> > Just to be clear: I'm not against this patch, we definitely
> > want to fix virQEMUCapsSupportsChardev(). What gave me pause
> > is simply the fact that you seemed to claim it made the
> > <console><log> feature usable, which I'm still unconvinced
> > is actually the case.
> 
> Oh, I didn't intend to claim that.  I intended to claim that
> 
> <serial type='pty'>
>     <log file='/tmp/testlogfile.log' append='off'/>
> <target port='0'/>
> 
> now works.

Well, that's the same thing, really :)

Adding <serial type='pty'/> will automatically add
<console type='pty'/>, so if one works the other should
work as well, since they translate to a single QEMU option
at the end of the day.

> I'm not sure where I claimed more beyond that, can you
> point me to specifics (this patch or the bug report, etc.) and I'll be
> happy to correct that?

https://bugs.linaro.org/show_bug.cgi?id=2777#c36

Also, twice in the message I'm replying to ;)

> At this point I'm a little confused about how to proceed here.  Would
> you like further evidence of an environment that reproduces the issue
> with console and the isa bus, with additional logic added to this
> patch to fix that, or should we get this patch merged and fix the
> other issue separately?

We can merge the patch without further changes to it, as
it fixes part of the issues that prevent the feature to work.

Actually, I just added

Reviewed-by: Andrea Bolognani <abologna at redhat.com>

and pushed it :)

> I'll try to look at reproducing the isa bus thing and seeing if I can
> come up with a fix when I'm back, unless someone beats me to it, which
> is not unlikely given the time it takes me to dig through libvirt
> abstraction layers.

I thought that fixing this would require QEMU changes, but
Drew recently pointed out[1] that it might be possible to
make it work using existing QEMU features only. I'll look
into that in the next few days.

Enjoy your vacation ^^


[1] https://bugzilla.redhat.com/show_bug.cgi?id=1456882#c4
-- 
Andrea Bolognani / Red Hat / Virtualization