Re: [Xen-devel] [PATCH for-4.7 2/2] tools/xendomains: Create lockfile on start unconditionally

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 11/05/16 12:14, George Dunlap wrote:
> At the moment, the xendomains init script will only create a lockfile
> if when started, it actually does something -- either tries to restore
> a previously saved domain as a result of XENDOMAINS_RESTORE, or tries
> to create a domain as a result of XENDOMAINS_AUTO.
> 
> RedHat-based SYSV init systems try to only call "${SERVICE} shutdown"
> on systems which actually have an actively running component; and they
> use the existence of /var/lock/subsys/${SERVICE} to determine which
> systems are running.
> 
> This means that at the moment, on RedHat-based SYSV systems (such as
> CentOS 6), if you enable xendomains, and have XENDOMAINS_RESTORE set
> to "true", but don't happen to start a VM, then your running VMs will
> not be suspended on shutdown.
> 
> Since the lockfile doesn't really have any other effect than to
> prevent duplicate starting, just create it unconditionally every time
> we start the xendomains script.
> 
> The other option would have been to touch the lockfile if
> XENDOMAINS_RESTORE was true regardless of whether there were any
> domains to be restored.  But this would mean that if you started with
> the xendomains script active but XENDOMAINS_RESTORE set to "false",
> and then changed it to "true", then xendomains would still not run the
> next time you shut down.  This seems to me to violate the principle of
> least surprise.
> 
> Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
> ---
> CC: Ian Jackson <ian.jackson@xxxxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Olaf Hering <olaf@xxxxxxxxx>

Forgot the release justification.

This is a bug in xendomains under RHEL sysv init systems -- albeit one
that's been there from the beginning.  Creating the lockfile
unconditionally shouldn't cause any problems as far as I can tell.

 -George

> ---
>  tools/hotplug/Linux/xendomains.in | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/hotplug/Linux/xendomains.in 
> b/tools/hotplug/Linux/xendomains.in
> index 727cd42..334d244 100644
> --- a/tools/hotplug/Linux/xendomains.in
> +++ b/tools/hotplug/Linux/xendomains.in
> @@ -255,12 +255,13 @@ start()
>       return;
>      fi
>  
> +    mkdir -p $(dirname "$LOCKFILE")
> +    touch $LOCKFILE
> +
>      saved_domains=" "
>      if [ "$XENDOMAINS_RESTORE" = "true" ] &&
>         contains_something "$XENDOMAINS_SAVE"
>      then
> -     mkdir -p $(dirname "$LOCKFILE")
> -     touch $LOCKFILE
>       echo -n "Restoring Xen domains:"
>       saved_domains=`ls $XENDOMAINS_SAVE`
>          for dom in $XENDOMAINS_SAVE/*; do
> @@ -286,7 +287,6 @@ start()
>  
>      if contains_something "$XENDOMAINS_AUTO"
>      then
> -     touch $LOCKFILE
>       echo -n "Starting auto Xen domains:"
>       # We expect config scripts for auto starting domains to be in
>       # XENDOMAINS_AUTO - they could just be symlinks to files elsewhere
> 


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel