docs: Document the real behaviour of suspend-to-{mem, disk}

[libvirt] [PATCH] docs: Document the real behaviour of suspend-to-{mem, disk}

Posted by Martin Kletzander 6 years, 6 months ago

We get a question every now and then about why hibernation works when
suspend-to-disk is disabled and similar.  Let's hope that, by documenting the
obvious more blatantly, people will get more informed.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
---
 docs/formatdomain.html.in | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index 5bdcb569c4c0..5dcf2fedb01c 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -1664,7 +1664,11 @@
       <dd>These elements enable ('yes') or disable ('no') BIOS support
         for S3 (suspend-to-mem) and S4 (suspend-to-disk) ACPI sleep
         states. If nothing is specified, then the hypervisor will be
-        left with its default value.</dd>
+        left with its default value.<br/>
+        Note: This setting cannot prevent the guest OS from performing
+        a suspend as the guest OS itself can choose to circumvent the
+        unavailability of the sleep states (e.g. S4 by turning off
+        completely).</dd>
     </dl>
 
     <h3><a id="elementsFeatures">Hypervisor features</a></h3>
-- 
2.14.2

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Re: [libvirt] [PATCH] docs: Document the real behaviour of suspend-to-{mem, disk}

Posted by Erik Skultety 6 years, 6 months ago

On Fri, Sep 29, 2017 at 02:55:05PM +0200, Martin Kletzander wrote:
> We get a question every now and then about why hibernation works when
> suspend-to-disk is disabled and similar.  Let's hope that, by documenting the
> obvious more blatantly, people will get more informed.
>
> Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
> ---
>  docs/formatdomain.html.in | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
> index 5bdcb569c4c0..5dcf2fedb01c 100644
> --- a/docs/formatdomain.html.in
> +++ b/docs/formatdomain.html.in
> @@ -1664,7 +1664,11 @@
>        <dd>These elements enable ('yes') or disable ('no') BIOS support
>          for S3 (suspend-to-mem) and S4 (suspend-to-disk) ACPI sleep
>          states. If nothing is specified, then the hypervisor will be
> -        left with its default value.</dd>
> +        left with its default value.<br/>
> +        Note: This setting cannot prevent the guest OS from performing
> +        a suspend as the guest OS itself can choose to circumvent the
> +        unavailability of the sleep states (e.g. S4 by turning off
> +        completely).</dd>
>      </dl>

So according to what I found, kernel can present shutdown as the default action
for hibernation support, maybe a bit strange to me, but documenting it
reasonable, I have to dig deeper though to understand the ACPI more.

Reviewed-by: Erik Skultety <eskultet@redhat.com>

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