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

[George Dunlap]

On Wed, May 11, 2016 at 12:14 PM, 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 

And this should probably be backported as far back as we're still
doing bugfixes (which I guess would be 4.6 and 4.5?)

 -George

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

[Olaf Hering]

On Wed, May 11, 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.

Acked-by: Olaf Hering 

Olaf

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

[Wei Liu]

On Wed, May 11, 2016 at 12:14:45PM +0100, 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 

Acked-by: Wei Liu 

> ---
> CC: Ian Jackson 
> CC: Wei Liu 
> CC: Olaf Hering 
> ---
>  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
> -- 
> 2.1.4
> 

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

[Wei Liu]

On Wed, May 11, 2016 at 12:19:45PM +0100, George Dunlap wrote:
> 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 
> > ---
> > CC: Ian Jackson 
> > CC: Wei Liu 
> > CC: Olaf Hering 
> 
> 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.
> 

I agree.

Release-acked-by: Wei Liu 

I've queued this series.

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

[George Dunlap]

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 
> ---
> CC: Ian Jackson 
> CC: Wei Liu 
> CC: Olaf Hering 

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
> 


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

[George Dunlap]

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 
---
CC: Ian Jackson 
CC: Wei Liu 
CC: Olaf Hering 
---
 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
-- 
2.1.4


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