Re: question about migration

[Ian Campbell <ian.campbell@citrix.com>]

On Mon, 2016-01-04 at 15:31 +0000, Ian Jackson wrote:
> [...]

>   The daemonic xl exits in this situation because it expects the
>   migration machinery to tidy up the domain.
> 
> * It is not possible to resume the domain in the source after it has
>   suspended.

Isn't supposed to be, isn't that why SCHEDOP_suspend returns a flag to
indicate if it was cancelled or not, so the guest can be resumed on the
source if "something" went wrong? (And isn't such a resume the same as what
happens after a checkpoint?)

Unless you are referring not to the general case but to some more specific
scenario/window where this is no longer possible?

>   The domain is, in the hypervisor, in the lifecycle state
>   SHUTDOWN.  For this reason in general, it is a bad idea to suspend
>   the guest until the migration is known to be likely to succeed.
> 
>   After a late migration failure the domain should probably be treated
>   as crashed.  This is slightly awkward to implement because the
>   daemonic xl would have to hang around to see what happened next and
>   perhaps be told what to do.  Or maybe the migrating xl would have to
>   know what the on_crash configuration was.
> 
>   In the meantime the failure is rather less graceful: debris is
>   simply left for the user.  This is not ideal but tolerable I think.
> 
> Ian.
> 
> 
> From 00c4fc6495078026d68f3fdd88bfd29a8ad483d7 Mon Sep 17 00:00:00 2001
> From: Ian Jackson <ian.jackson@eu.citrix.com>
> Date: Mon, 4 Jan 2016 15:13:14 +0000
> Subject: [PATCH] libxl: Fix doc comment ref to DOMAIN_DEATH
> 
> The doc comment for libxl_evdisable_domain_death mistakenly referred
> to DOMAIN_DESTROY but the event type name is actually DOMAIN_DEATH.
> 
> Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
> CC: Andrew Cooper <andrew.cooper3@citrix.com>
> ---
>  tools/libxl/libxl_event.h |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/libxl/libxl_event.h b/tools/libxl/libxl_event.h
> index fad4c14..1ea789e 100644
> --- a/tools/libxl/libxl_event.h
> +++ b/tools/libxl/libxl_event.h
> @@ -179,9 +179,9 @@ typedef struct libxl__evgen_domain_death
> libxl_evgen_domain_death;
>  int libxl_evenable_domain_death(libxl_ctx *ctx, uint32_t domid,
>                           libxl_ev_user, libxl_evgen_domain_death
> **evgen_out);
>  void libxl_evdisable_domain_death(libxl_ctx *ctx,
> libxl_evgen_domain_death*);
> -  /* Arranges for the generation of DOMAIN_SHUTDOWN and DOMAIN_DESTROY
> +  /* Arranges for the generation of DOMAIN_SHUTDOWN and DOMAIN_DEATH
>     * events.  A domain which is destroyed before it shuts down
> -   * may generate only a DESTROY event.
> +   * may generate only a DEATH event.
>     */
>  
>  typedef struct libxl__evgen_disk_eject libxl_evgen_disk_eject;

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