Re: [libvirt] [PATCH] qemu: add support for error messages greater than 1024 characters

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(a)virtualopensystems.com&gt; > --- > 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.

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.