On Mon, Dec 16, 2013 at 10:35:58AM +0100, Peter Krempa wrote:
> On 12/16/13 10:27, Laine Stump wrote:
> > On 12/14/2013 07:15 PM, Cole Robinson wrote:
> >> On 12/11/2013 03:33 PM, Michele Paolino wrote:
> >>> In libvirt, the default error message length is 1024 bytes. This is not
> >>> enough for qemu to print long error messages such as the list of
> >>> supported ARM machine models (more than 1700 chars). This is
> >>> raised when the machine entry in the XML file is wrong, but there may
> >>> be now or in future other verbose error messages.
> >>> The above patch enables libvirt to print error messages >1024 for qemu.
> >>>
> >>> Signed-off-by: Michele Paolino <m.paolino@xxxxxxxxxxxxxxxxxxxxxx>
> >>> ---
> >>> src/qemu/qemu_process.c | 23 +++++++++++++++++++----
> >>> 1 file changed, 19 insertions(+), 4 deletions(-)
> >>>
> >>> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> >>> index bd9546e..c2e2136 100644
> >>> --- a/src/qemu/qemu_process.c
> >>> +++ b/src/qemu/qemu_process.c
> >>> @@ -1904,10 +1904,25 @@ cleanup:
> >>> * a possible read of the fd in the monitor code doesn't influence this
> >>> * error delivery option */
> >>> ignore_value(lseek(logfd, pos, SEEK_SET));
> >>> - qemuProcessReadLog(logfd, buf + len, buf_size - len - 1, 0, true);
> >>> - virReportError(VIR_ERR_INTERNAL_ERROR,
> >>> - _("process exited while connecting to monitor: %s"),
> >>> - buf);
> >>> + len = qemuProcessReadLog(logfd, buf + len, buf_size - len - 1, 0, true);
> >>> +
> >>> + /* virReportError error buffer is limited to 1024 byte*/
> >>> + if (len < 1024){
> >>> + virReportError(VIR_ERR_INTERNAL_ERROR,
> >>> + _("process exited while connecting to monitor: %s"),
> >>> + buf);
> >>> + } else {
> >>> + if (STRPREFIX(buf, "Supported machines are:"))
> >>> + virReportError(VIR_ERR_INTERNAL_ERROR,
> >>> + _("process exited while connecting to monitor:"
> >>> + "please check machine model"));
> >>> + else
> >>> + virReportError(VIR_ERR_INTERNAL_ERROR,
> >>> + _("process exited while connecting to monitor"));
> >>> +
> >>> + VIR_ERROR("%s", buf);
> >>> + }
> >>> +
> >>> ret = -1;
> >>> }
> >>>
> >>>
> >> This kind of error scraping is a slipper slop IMO, and for this particular
> >> case I don't think it's even that interesting.
> >
> > I definitely agree with that.
> >
> >>
> >> Libvirt already parses the machine types for each qemu emulator and reports it
> >> in virsh capabilities XML. Seems reasonable that we could validate the XML
> >> machine type at define time and catch an invalid machine type error long
> >> before we even try and start the VM.
> >
> > Do we really want to refuse to define a particular guest just because
> > the host where we're defining it doesn't currently support the given
> > machine type? That's yet another slippery slope - for example, should we
> > also be validating all the devices in <hostdev> at definition time? I
> > think the proper time to do that validation is at domain start time when
> > we should have the proper qemu binary (and necessary drivers/hardware)
> > available.
>
> I'd say we want to do stuff like this when starting a VM rather than
> defining it. We have a precedent where we check the count of CPUs
> supported by the emulator when we start the VM rather than at define
> time. This allows us to craft a useful error message but doesn't forbid
> to define a guest and then upgrade the emulator to a version that
> supports all the stuff necessary.
Agreed, doing it at start time is best IMHO.
Daniel
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