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

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.

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 &&