Re: [libvirt] [PATCH RFC] libxl: set serial source path for console type=serial

On 06/21/2016 10:32 PM, Jim Fehlig wrote: > On 06/21/2016 04:20 AM, Joao Martins wrote: >> On 06/21/2016 01:38 AM, Jim Fehlig wrote: >>> Joao Martins wrote: >>>> Guests use a <console /> (and sometimes <serial /> pair) to represent >>>> the console. On the callback that is called when console is brought up >>>> (NB: before domain starts), we fill the path of the console element with >>>> the appropriate "/dev/pts/X". For PV guests it all works fine, although >>>> for HVM guests it doesn't. Consequently we end up seeing erronous >>>> behaviour on HVM guests where console path is not displayed on the XML >>>> but still can be accessed with virDomainOpenConsole after booting guest. >>>> Consumers of this XML (e.g. Openstack) also won't be able to use the >>>> console path. >>> Can you provide example input domXML config that causes this problem? >>> >> Ah yes - I probably should include that in the commit description? > Yes, I think it helps clarify the problem being solved by the commit. > >> So, for PV guests for an input console XML element: >> >> <console type='pty'> >> <target type='xen' port='0'/> >> </console> >> >> Which then on domain start gets filled like: >> >> <console type='pty' tty='/dev/pts/3'> >> <source path='/dev/pts/3'/> >> <target type='xen' port='0'/> >> </console> >> >> Although for HVM guests we have: >> >> <serial type='pty'> >> <target port='0'/> >> </serial> >> <console type='pty'> >> <target type='serial' port='0'/> >> </console> >> >> And no changes happen i.e. source path isn't written there _even though_ it's >> set on the console element - being the reason why we can access the console in the >> first place. IIUC The expected output should be: >> >> <serial type='pty'> >> <source path='/dev/pts/4'/> >> <target port='0'/> >> </serial> >> <console type='pty' tty='/dev/pts/4'> >> <source path='/dev/pts/4'/> >> <target type='serial' port='0'/> >> </console> > I asked for an example after having problems testing your patch, but it turned > out to be an issue which I think was introduced long ago by commit 482e5f15. I > was testing with transient domains and noticed 'virsh create; 'virsh console' > always failed with > > error: internal error: character device <null> is not using a PTY > > My config only contained > > <console type='pty'> > <target port='0'/> > </console> > > so the "really crazy backcompat stuff for consoles" in > virDomainDefAddConsoleCompat() moved the config over to def->serials[0] and > created a new def->consoles[0] without def->consoles[0].source.type set to > VIR_DOMAIN_CHR_TYPE_PTY. Without source.type set, libxlConsoleCallback() would > ignore the console and not copy the PTY path to source.data.file.path. 'virsh > console' would then fail with the error noted above. > > I spent too much time debugging this, partly because I was confused by odd > behavior with persistent domains. E.g. 'virsh define; virsh start; virsh > console' would fail with the same error, but all subsequent 'virsh shutdown; > virsh start; virsh console' sequences would work :-). That behavior was due to > vm->newDef being populated with correct console config when calling > virDomainObjSetDefTransient() in libxlDomainStart(). After the first shutdown of > the domain, vm->newDef would be copied over to vm->def, allowing subsequent > 'virsh start; virsh console' to work correctly. > Hmm, that sounds weird. Can you explain more how exactly the XML changes?

What is the diff between the initial 'virsh define; virsh dumpxml'

and the dumpxml after the VM has started+shutdown once? Whatever that diff is, and why it's not in the XML to begin with, sounds like the root issue to me. > Long story short, I found the problem but not sure how to fix it :-). One > approach would be the below patch. Another would be to loosen the restriction in > libxlConsoleCallback, filing in source.data.file.path when the console source > type is also set to VIR_DOMAIN_CHR_TYPE_NULL. Adding Cole and Peter (both of > which have toiled in and likely loathe this code) to see if they have opinions > on a proper fix. > > Regards, > Jim > > > From a231636e8eec08152220e32af5f4026a50954f41 Mon Sep 17 00:00:00 2001 > From: Jim Fehlig <jfehlig(a)suse.com&gt; > Date: Tue, 21 Jun 2016 20:25:23 -0600 > Subject: [PATCH] domain conf: copy source type from stolen console > > When domXML contains only <console type='pty'> and no corresponding > <serial>, the console is "stolen" [1] and used as the first <serial> > device. A new console is created as an alias to the first <serial> > device, but missed copying some configuration such as the source > 'type' attribute. > > [1] See comments associated with virDomainDefAddConsoleCompat() in > $LIBVIRT-SRC/src/conf/domain_conf.c: > > Signed-off-by: Jim Fehlig <jfehlig(a)suse.com&gt; > --- > src/conf/domain_conf.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c > index 75ad03f..2fda4fe 100644 > --- a/src/conf/domain_conf.c > +++ b/src/conf/domain_conf.c > @@ -3845,6 +3845,7 @@ virDomainDefAddConsoleCompat(virDomainDefPtr def) > /* Create an console alias for the serial port */ > def->consoles[0]->deviceType = VIR_DOMAIN_CHR_DEVICE_TYPE_CONSOLE; > def->consoles[0]->targetType = > VIR_DOMAIN_CHR_CONSOLE_TARGET_TYPE_SERIAL; > + def->consoles[0]->source.type = def->serials[0]->source.type; > } > } else if (def->os.type == VIR_DOMAIN_OSTYPE_HVM && def->nserials > 0 && > def->serials[0]->deviceType == VIR_DOMAIN_CHR_DEVICE_TYPE_SERIAL && > Then again this also seems okay to me, but it's concerning that I applied this but it didn't cause the test suite to change at all. - Cole