Re: [libvirt] [PATCH v3 4/7] qemu: Translate the iscsi pool/volume disk source

Il 23/07/2013 18:47, John Ferlan ha scritto: > On 07/23/2013 12:18 PM, Paolo Bonzini wrote: >> Il 23/07/2013 18:01, Daniel P. Berrange ha scritto: >>> On Tue, Jul 23, 2013 at 05:35:57PM +0200, Paolo Bonzini wrote: >>>> Il 23/07/2013 16:14, Daniel P. Berrange ha scritto: >>>>>>> Perhaps the default could be specified in a configuration file (and the >>>>>>> default should be the safe one). >>>>> No, that is even worse because now the default is not predictable.. >>>>> >>>>> We simply default to host mode and if applications want to use the >>>>> other mode they can configure the XML as desired. >>>> Can we just forbid mode='default' for iSCSI and force the user to >>>> specify host vs. direct? >>> That would mean that apps cannot simply configure a guest volume >>> without first checking to find out what type of pool it is, and >>> then specifying this extra arg for iSCSI. IMHO the value of the >>> <volume> XML is that you don't have to know anything about the >>> pool to be able to configure it - we're completely decoupled. >> Thinking more about it, it would only be needed for <disk type='volume' >> device='lun'>. And for that case, some knowledge of the pool is >> necessary anyway (for one thing, it won't work with filesystem or LVM >> pools). So if we could forbid mode='default' for that case only, it >> would be enough as far as I'm concernde. > Using "default" in the mode field would result in the following XML > error message (I just quickly changed a test to prove the point): > > 121) QEMU XML-2-XML disk-source-pool-mode > ... libvirt: Domain Config error : XML error: unknown source mode > 'default' for volume type disk > FAILED Sorry, by mode='default' I really meant "no mode at all" (I was under the false impression that you could also specify a mode='default' with the same effect as no mode at all). > The XML parsing code only looks for "mode='direct'" or "mode='host'". If > "mode" isn't present in the XML, that's when that default comes into > play. Since 'mode' is new there could be configurations where its not in > an XML file, thus a 0 (zero e.g. "default") value is provided for the field. > > Once the XML is parsed we still needed a default when it's going to be > added, thus the "magic" to set the default to HOST is in qemu_conf.c in > qemuTranslateDiskSourcePool(): > > > if (pooldef->type == VIR_STORAGE_POOL_ISCSI) { > /* Default to use the LUN's path on host */ > if (!def->srcpool->mode) > def->srcpool->mode = VIR_DOMAIN_DISK_SOURCE_POOL_MODE_HOST; > > > I think this answers your primary concern - correct? No, my concern is that mode='host' is a bad default for the device='lun' case.