Re: [Xen-devel] [PATCH V2] libxl: Set path to console on domain startup.

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-12-11 at 16:16 +0000, Anthony PERARD wrote:
> On Tue, Dec 09, 2014 at 03:56:02PM +0000, Ian Campbell wrote:
> > On Tue, 2014-12-09 at 15:39 +0000, Anthony PERARD wrote:
> > > The path to the pty of a Xen PV console is set only in
> > > virDomainOpenConsole. But this is done too late. A call to
> > > virDomainGetXMLDesc done before OpenConsole will not have the path to
> > > the pty, but a call after OpenConsole will.
> > > 
> > > e.g. of the current issue.
> > > Starting a domain with '<console type="pty"/>'
> > > Then:
> > > virDomainGetXMLDesc():
> > >   <devices>
> > >     <console type='pty'>
> > >       <target type='xen' port='0'/>
> > >     </console>
> > >   </devices>
> > > virDomainOpenConsole()
> > > virDomainGetXMLDesc():
> > >   <devices>
> > >     <console type='pty' tty='/dev/pts/30'>
> > >       <source path='/dev/pts/30'/>
> > >       <target type='xen' port='0'/>
> > >     </console>
> > >   </devices>
> > > 
> > > The patch intend to have the TTY path on the first call of GetXMLDesc.
> > > This is done by setting up the path at domain start up instead of in
> > > OpenConsole.
> > > 
> > > https://bugzilla.redhat.com/show_bug.cgi?id=1170743
> > > 
> > > Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> > > 
> > > ---
> > > Change in V2:
> > >   Adding bug report link.
> > >   Reword the last part of the patch description.
> > >   Cleanup the code.
> > >   Use VIR_FREE before VIR_STRDUP.
> > >   Remove the code from OpenConsole as it is now a duplicate.
> > > ---
> > >  src/libxl/libxl_domain.c | 20 ++++++++++++++++++++
> > >  src/libxl/libxl_driver.c | 15 ---------------
> > >  2 files changed, 20 insertions(+), 15 deletions(-)
> > > 
> > > diff --git a/src/libxl/libxl_domain.c b/src/libxl/libxl_domain.c
> > > index 9c62291..325de79 100644
> > > --- a/src/libxl/libxl_domain.c
> > > +++ b/src/libxl/libxl_domain.c
> > > @@ -1290,6 +1290,26 @@ libxlDomainStart(libxlDriverPrivatePtr driver, 
> > > virDomainObjPtr vm,
> > >      if (libxlDomainSetVcpuAffinities(driver, vm) < 0)
> > >          goto cleanup_dom;
> > >  
> > > +    if (vm->def->nconsoles) {
> > > +        virDomainChrDefPtr chr = vm->def->consoles[0];
> > 
> > Given vm->def->nconsoles should we loop and do them all?
> 
> Maybe. libvirt it self will not be able to access any console that is
> not the first one (virDomainOpenConsole only provide access to console
> 0), but a consumer of libvirt could.
> 
> > Also, and I really should know the answer to this (and sorry for not
> > thinking of it earlier), but:
> > 
> > > +            ret = libxl_console_get_tty(priv->ctx, vm->def->id,
> > > +                                        chr->target.port, console_type,
> > > +                                        &console);
> > 
> > Might this race against xenconsoled writing the node to xenstore and
> > therefore be prone to failing when starting multiple guests all at once?
> 
> I've look through out libxl, xenconsoled and libvirt, and I could not
> find any synchronisation point. So I guest it's possible.
> 
> > Is there a hook which is called on virsh dumpxml which could update
> > things on the fly (i.e. lookup the console iff it isn't already set)?
> 
> I guest we could modify libxlDomainGetXMLDesc and libxlDomainOpenConsole
> to do the check, or having a xenstore watch on the path (if that is
> possible).

The aop_console_how option to libxl_domain_create_new and
libxl_domain_create_restore is documented as:

  /* A progress report will be made via ao_console_how, of type
   * domain_create_console_available, when the domain's primary
   * console is available and can be connected to.
   */

Which sounds like exactly what is needed?

Ian.


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