This reverts commit 3df663e575f1876d7f3bc684f80e72fca0703d39.
This reverts commit b605c47b57b58e61a901a50a0762dccf43d94783.

Command line option --only-migratable is for disallowing any
configuration that can block migration.

Initially, --only-migratable set global variable @only_migratable.

Commit 3df663e575 "migration: move only_migratable to MigrationState"
replaced it by MigrationState member @only_migratable.  That was a
mistake.

First, it doesn't make sense on the design level.  MigrationState
captures the state of an individual migration, but --only-migratable
isn't a property of an individual migration, it's a restriction on
QEMU configuration.  With fault tolerance, we could have several
migrations at once.  --only-migratable would certainly protect all of
them.  Storing it in MigrationState feels inappropriate.

Second, it contributes to a dependency cycle that manifests itself as
a bug now.

Putting @only_migratable into MigrationState means its available only
after migration_object_init().

We can't set it before migration_object_init(), so we delay setting it
with a global property (this is fixup commit b605c47b57 "migration:
fix handling for --only-migratable").

We can't get it before migration_object_init(), so anything that uses
it can only run afterwards.

Since migrate_add_blocker() needs to obey --only-migratable, any code
adding migration blockers can run only afterwards.  This contributes
to the following dependency cycle:

* configure_blockdev() must run before machine_set_property()
  so machine properties can refer to block backends

* machine_set_property() before configure_accelerator()
  so machine properties like kvm-irqchip get applied

* configure_accelerator() before migration_object_init()
  so that Xen's accelerator compat properties get applied.

* migration_object_init() before configure_blockdev()
  so configure_blockdev() can add migration blockers

The cycle was closed when recent commit cda4aa9a5a0 "Create block
backends before setting machine properties" added the first
dependency, and satisfied it by violating the last one.  Broke block
backends that add migration blockers.

Moving @only_migratable into MigrationState was a mistake.  Revert it.

This doesn't quite break the "migration_object_init() before
configure_blockdev() dependency, since migrate_add_blocker() still has
another dependency on migration_object_init().  To be addressed the
next commit

Conflicts:
	include/migration/misc.h
	migration/migration.c
	migration/migration.h
	vl.c

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 include/sysemu/sysemu.h | 1 +
 migration/migration.c   | 5 ++---
 migration/migration.h   | 3 ---
 migration/savevm.c      | 2 +-
 vl.c                    | 9 ++-------
 5 files changed, 6 insertions(+), 14 deletions(-)

diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 6065d9e420..5f133cae83 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -14,6 +14,7 @@
 /* vl.c */
 
 extern const char *bios_name;
+extern int only_migratable;
 extern const char *qemu_name;
 extern QemuUUID qemu_uuid;
 extern bool qemu_uuid_set;
diff --git a/migration/migration.c b/migration/migration.c
index 69f75124c9..f6076e5295 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1707,7 +1707,7 @@ static GSList *migration_blockers;
 
 int migrate_add_blocker(Error *reason, Error **errp)
 {
-    if (migrate_get_current()->only_migratable) {
+    if (only_migratable) {
         error_propagate_prepend(errp, error_copy(reason),
                                 "disallowing migration blocker "
                                 "(--only_migratable) for: ");
@@ -3337,7 +3337,7 @@ void migration_global_dump(Monitor *mon)
     monitor_printf(mon, "store-global-state: %s\n",
                    ms->store_global_state ? "on" : "off");
     monitor_printf(mon, "only-migratable: %s\n",
-                   ms->only_migratable ? "on" : "off");
+                   only_migratable ? "on" : "off");
     monitor_printf(mon, "send-configuration: %s\n",
                    ms->send_configuration ? "on" : "off");
     monitor_printf(mon, "send-section-footer: %s\n",
@@ -3352,7 +3352,6 @@ void migration_global_dump(Monitor *mon)
 static Property migration_properties[] = {
     DEFINE_PROP_BOOL("store-global-state", MigrationState,
                      store_global_state, true),
-    DEFINE_PROP_BOOL("only-migratable", MigrationState, only_migratable, false),
     DEFINE_PROP_BOOL("send-configuration", MigrationState,
                      send_configuration, true),
     DEFINE_PROP_BOOL("send-section-footer", MigrationState,
diff --git a/migration/migration.h b/migration/migration.h
index 0f986935e1..438f17edad 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -219,9 +219,6 @@ struct MigrationState
      */
     bool store_global_state;
 
-    /* Whether the VM is only allowing for migratable devices */
-    bool only_migratable;
-
     /* Whether we send QEMU_VM_CONFIGURATION during migration */
     bool send_configuration;
     /* Whether we send section footer during migration */
diff --git a/migration/savevm.c b/migration/savevm.c
index 1415001d1c..34bcad3807 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2844,7 +2844,7 @@ void vmstate_register_ram_global(MemoryRegion *mr)
 bool vmstate_check_only_migratable(const VMStateDescription *vmsd)
 {
     /* check needed if --only-migratable is specified */
-    if (!migrate_get_current()->only_migratable) {
+    if (!only_migratable) {
         return true;
     }
 
diff --git a/vl.c b/vl.c
index c1d5484e12..e4d7ad6b85 100644
--- a/vl.c
+++ b/vl.c
@@ -185,6 +185,7 @@ const char *prom_envs[MAX_PROM_ENVS];
 int boot_menu;
 bool boot_strict;
 uint8_t *boot_splash_filedata;
+int only_migratable; /* turn it off unless user states otherwise */
 bool wakeup_suspend_enabled;
 
 int icount_align_option;
@@ -3799,13 +3800,7 @@ int main(int argc, char **argv, char **envp)
                 incoming = optarg;
                 break;
             case QEMU_OPTION_only_migratable:
-                /*
-                 * TODO: we can remove this option one day, and we
-                 * should all use:
-                 *
-                 * "-global migration.only-migratable=true"
-                 */
-                qemu_global_option("migration.only-migratable=true");
+                only_migratable = 1;
                 break;
             case QEMU_OPTION_nodefaults:
                 has_defaults = 0;
-- 
2.17.2

* Markus Armbruster (armbru@redhat.com) wrote:
> This reverts commit 3df663e575f1876d7f3bc684f80e72fca0703d39.
> This reverts commit b605c47b57b58e61a901a50a0762dccf43d94783.
> 
> Command line option --only-migratable is for disallowing any
> configuration that can block migration.
> 
> Initially, --only-migratable set global variable @only_migratable.
> 
> Commit 3df663e575 "migration: move only_migratable to MigrationState"
> replaced it by MigrationState member @only_migratable.  That was a
> mistake.
> 
> First, it doesn't make sense on the design level.  MigrationState
> captures the state of an individual migration, but --only-migratable
> isn't a property of an individual migration, it's a restriction on
> QEMU configuration.  With fault tolerance, we could have several
> migrations at once.  --only-migratable would certainly protect all of
> them.  Storing it in MigrationState feels inappropriate.
> 
> Second, it contributes to a dependency cycle that manifests itself as
> a bug now.
> 
> Putting @only_migratable into MigrationState means its available only
> after migration_object_init().
> 
> We can't set it before migration_object_init(), so we delay setting it
> with a global property (this is fixup commit b605c47b57 "migration:
> fix handling for --only-migratable").
> 
> We can't get it before migration_object_init(), so anything that uses
> it can only run afterwards.
> 
> Since migrate_add_blocker() needs to obey --only-migratable, any code
> adding migration blockers can run only afterwards.  This contributes
> to the following dependency cycle:
> 
> * configure_blockdev() must run before machine_set_property()
>   so machine properties can refer to block backends
> 
> * machine_set_property() before configure_accelerator()
>   so machine properties like kvm-irqchip get applied
> 
> * configure_accelerator() before migration_object_init()
>   so that Xen's accelerator compat properties get applied.
> 
> * migration_object_init() before configure_blockdev()
>   so configure_blockdev() can add migration blockers
> 
> The cycle was closed when recent commit cda4aa9a5a0 "Create block
> backends before setting machine properties" added the first
> dependency, and satisfied it by violating the last one.  Broke block
> backends that add migration blockers.
> 
> Moving @only_migratable into MigrationState was a mistake.  Revert it.
> 
> This doesn't quite break the "migration_object_init() before
> configure_blockdev() dependency, since migrate_add_blocker() still has
> another dependency on migration_object_init().  To be addressed the
> next commit
> 
> Conflicts:
> 	include/migration/misc.h
> 	migration/migration.c
> 	migration/migration.h
> 	vl.c
> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
>  include/sysemu/sysemu.h | 1 +
>  migration/migration.c   | 5 ++---
>  migration/migration.h   | 3 ---
>  migration/savevm.c      | 2 +-
>  vl.c                    | 9 ++-------
>  5 files changed, 6 insertions(+), 14 deletions(-)
> 
> diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> index 6065d9e420..5f133cae83 100644
> --- a/include/sysemu/sysemu.h
> +++ b/include/sysemu/sysemu.h
> @@ -14,6 +14,7 @@
>  /* vl.c */
>  
>  extern const char *bios_name;
> +extern int only_migratable;
>  extern const char *qemu_name;
>  extern QemuUUID qemu_uuid;
>  extern bool qemu_uuid_set;
> diff --git a/migration/migration.c b/migration/migration.c
> index 69f75124c9..f6076e5295 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1707,7 +1707,7 @@ static GSList *migration_blockers;
>  
>  int migrate_add_blocker(Error *reason, Error **errp)
>  {
> -    if (migrate_get_current()->only_migratable) {
> +    if (only_migratable) {
>          error_propagate_prepend(errp, error_copy(reason),
>                                  "disallowing migration blocker "
>                                  "(--only_migratable) for: ");
> @@ -3337,7 +3337,7 @@ void migration_global_dump(Monitor *mon)
>      monitor_printf(mon, "store-global-state: %s\n",
>                     ms->store_global_state ? "on" : "off");
>      monitor_printf(mon, "only-migratable: %s\n",
> -                   ms->only_migratable ? "on" : "off");
> +                   only_migratable ? "on" : "off");
>      monitor_printf(mon, "send-configuration: %s\n",
>                     ms->send_configuration ? "on" : "off");
>      monitor_printf(mon, "send-section-footer: %s\n",
> @@ -3352,7 +3352,6 @@ void migration_global_dump(Monitor *mon)
>  static Property migration_properties[] = {
>      DEFINE_PROP_BOOL("store-global-state", MigrationState,
>                       store_global_state, true),
> -    DEFINE_PROP_BOOL("only-migratable", MigrationState, only_migratable, false),

So I'm generally OK at this patch, but I'm worried whether this
is API?

Dave

>      DEFINE_PROP_BOOL("send-configuration", MigrationState,
>                       send_configuration, true),
>      DEFINE_PROP_BOOL("send-section-footer", MigrationState,
> diff --git a/migration/migration.h b/migration/migration.h
> index 0f986935e1..438f17edad 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -219,9 +219,6 @@ struct MigrationState
>       */
>      bool store_global_state;
>  
> -    /* Whether the VM is only allowing for migratable devices */
> -    bool only_migratable;
> -
>      /* Whether we send QEMU_VM_CONFIGURATION during migration */
>      bool send_configuration;
>      /* Whether we send section footer during migration */
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 1415001d1c..34bcad3807 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -2844,7 +2844,7 @@ void vmstate_register_ram_global(MemoryRegion *mr)
>  bool vmstate_check_only_migratable(const VMStateDescription *vmsd)
>  {
>      /* check needed if --only-migratable is specified */
> -    if (!migrate_get_current()->only_migratable) {
> +    if (!only_migratable) {
>          return true;
>      }
>  
> diff --git a/vl.c b/vl.c
> index c1d5484e12..e4d7ad6b85 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -185,6 +185,7 @@ const char *prom_envs[MAX_PROM_ENVS];
>  int boot_menu;
>  bool boot_strict;
>  uint8_t *boot_splash_filedata;
> +int only_migratable; /* turn it off unless user states otherwise */
>  bool wakeup_suspend_enabled;
>  
>  int icount_align_option;
> @@ -3799,13 +3800,7 @@ int main(int argc, char **argv, char **envp)
>                  incoming = optarg;
>                  break;
>              case QEMU_OPTION_only_migratable:
> -                /*
> -                 * TODO: we can remove this option one day, and we
> -                 * should all use:
> -                 *
> -                 * "-global migration.only-migratable=true"
> -                 */
> -                qemu_global_option("migration.only-migratable=true");
> +                only_migratable = 1;
>                  break;
>              case QEMU_OPTION_nodefaults:
>                  has_defaults = 0;
> -- 
> 2.17.2
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

On Mon, Apr 01, 2019 at 10:27:49AM +0100, Dr. David Alan Gilbert wrote:
> * Markus Armbruster (armbru@redhat.com) wrote:
> > This reverts commit 3df663e575f1876d7f3bc684f80e72fca0703d39.
> > This reverts commit b605c47b57b58e61a901a50a0762dccf43d94783.
> > 
> > Command line option --only-migratable is for disallowing any
> > configuration that can block migration.
> > 
> > Initially, --only-migratable set global variable @only_migratable.
> > 
> > Commit 3df663e575 "migration: move only_migratable to MigrationState"
> > replaced it by MigrationState member @only_migratable.  That was a
> > mistake.
> > 
> > First, it doesn't make sense on the design level.  MigrationState
> > captures the state of an individual migration, but --only-migratable
> > isn't a property of an individual migration, it's a restriction on
> > QEMU configuration.  With fault tolerance, we could have several
> > migrations at once.  --only-migratable would certainly protect all of
> > them.  Storing it in MigrationState feels inappropriate.
> > 
> > Second, it contributes to a dependency cycle that manifests itself as
> > a bug now.
> > 
> > Putting @only_migratable into MigrationState means its available only
> > after migration_object_init().
> > 
> > We can't set it before migration_object_init(), so we delay setting it
> > with a global property (this is fixup commit b605c47b57 "migration:
> > fix handling for --only-migratable").
> > 
> > We can't get it before migration_object_init(), so anything that uses
> > it can only run afterwards.
> > 
> > Since migrate_add_blocker() needs to obey --only-migratable, any code
> > adding migration blockers can run only afterwards.  This contributes
> > to the following dependency cycle:
> > 
> > * configure_blockdev() must run before machine_set_property()
> >   so machine properties can refer to block backends
> > 
> > * machine_set_property() before configure_accelerator()
> >   so machine properties like kvm-irqchip get applied
> > 
> > * configure_accelerator() before migration_object_init()
> >   so that Xen's accelerator compat properties get applied.
> > 
> > * migration_object_init() before configure_blockdev()
> >   so configure_blockdev() can add migration blockers
> > 
> > The cycle was closed when recent commit cda4aa9a5a0 "Create block
> > backends before setting machine properties" added the first
> > dependency, and satisfied it by violating the last one.  Broke block
> > backends that add migration blockers.
> > 
> > Moving @only_migratable into MigrationState was a mistake.  Revert it.
> > 
> > This doesn't quite break the "migration_object_init() before
> > configure_blockdev() dependency, since migrate_add_blocker() still has
> > another dependency on migration_object_init().  To be addressed the
> > next commit
> > 
> > Conflicts:
> > 	include/migration/misc.h
> > 	migration/migration.c
> > 	migration/migration.h
> > 	vl.c
> > 
> > Signed-off-by: Markus Armbruster <armbru@redhat.com>
> > ---
> >  include/sysemu/sysemu.h | 1 +
> >  migration/migration.c   | 5 ++---
> >  migration/migration.h   | 3 ---
> >  migration/savevm.c      | 2 +-
> >  vl.c                    | 9 ++-------
> >  5 files changed, 6 insertions(+), 14 deletions(-)
> > 
> > diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> > index 6065d9e420..5f133cae83 100644
> > --- a/include/sysemu/sysemu.h
> > +++ b/include/sysemu/sysemu.h
> > @@ -14,6 +14,7 @@
> >  /* vl.c */
> >  
> >  extern const char *bios_name;
> > +extern int only_migratable;
> >  extern const char *qemu_name;
> >  extern QemuUUID qemu_uuid;
> >  extern bool qemu_uuid_set;
> > diff --git a/migration/migration.c b/migration/migration.c
> > index 69f75124c9..f6076e5295 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -1707,7 +1707,7 @@ static GSList *migration_blockers;
> >  
> >  int migrate_add_blocker(Error *reason, Error **errp)
> >  {
> > -    if (migrate_get_current()->only_migratable) {
> > +    if (only_migratable) {
> >          error_propagate_prepend(errp, error_copy(reason),
> >                                  "disallowing migration blocker "
> >                                  "(--only_migratable) for: ");
> > @@ -3337,7 +3337,7 @@ void migration_global_dump(Monitor *mon)
> >      monitor_printf(mon, "store-global-state: %s\n",
> >                     ms->store_global_state ? "on" : "off");
> >      monitor_printf(mon, "only-migratable: %s\n",
> > -                   ms->only_migratable ? "on" : "off");
> > +                   only_migratable ? "on" : "off");
> >      monitor_printf(mon, "send-configuration: %s\n",
> >                     ms->send_configuration ? "on" : "off");
> >      monitor_printf(mon, "send-section-footer: %s\n",
> > @@ -3352,7 +3352,6 @@ void migration_global_dump(Monitor *mon)
> >  static Property migration_properties[] = {
> >      DEFINE_PROP_BOOL("store-global-state", MigrationState,
> >                       store_global_state, true),
> > -    DEFINE_PROP_BOOL("only-migratable", MigrationState, only_migratable, false),
> 
> So I'm generally OK at this patch, but I'm worried whether this
> is API?

IIUC, old code can use either

  -global migration.only-migratable=true
  -only-migratable

After this patch only

  -only-migratable

is valid. So from that POV it is an API break. 

From libvirt's POV this is a non-issue as we never use either of these options.
We did have a BZ filed to support it, but never did.

To avoid the API break I guess there would been to be a special case early
loop iterating over argv[] looking for '-global migration.only-migratable=true',
making that set the static 'bool only_migratable', instead of letting it get
handled by the object infra.


> >      DEFINE_PROP_BOOL("send-configuration", MigrationState,
> >                       send_configuration, true),
> >      DEFINE_PROP_BOOL("send-section-footer", MigrationState,
> > diff --git a/migration/migration.h b/migration/migration.h
> > index 0f986935e1..438f17edad 100644
> > --- a/migration/migration.h
> > +++ b/migration/migration.h
> > @@ -219,9 +219,6 @@ struct MigrationState
> >       */
> >      bool store_global_state;
> >  
> > -    /* Whether the VM is only allowing for migratable devices */
> > -    bool only_migratable;
> > -
> >      /* Whether we send QEMU_VM_CONFIGURATION during migration */
> >      bool send_configuration;
> >      /* Whether we send section footer during migration */
> > diff --git a/migration/savevm.c b/migration/savevm.c
> > index 1415001d1c..34bcad3807 100644
> > --- a/migration/savevm.c
> > +++ b/migration/savevm.c
> > @@ -2844,7 +2844,7 @@ void vmstate_register_ram_global(MemoryRegion *mr)
> >  bool vmstate_check_only_migratable(const VMStateDescription *vmsd)
> >  {
> >      /* check needed if --only-migratable is specified */
> > -    if (!migrate_get_current()->only_migratable) {
> > +    if (!only_migratable) {
> >          return true;
> >      }
> >  
> > diff --git a/vl.c b/vl.c
> > index c1d5484e12..e4d7ad6b85 100644
> > --- a/vl.c
> > +++ b/vl.c
> > @@ -185,6 +185,7 @@ const char *prom_envs[MAX_PROM_ENVS];
> >  int boot_menu;
> >  bool boot_strict;
> >  uint8_t *boot_splash_filedata;
> > +int only_migratable; /* turn it off unless user states otherwise */
> >  bool wakeup_suspend_enabled;
> >  
> >  int icount_align_option;
> > @@ -3799,13 +3800,7 @@ int main(int argc, char **argv, char **envp)
> >                  incoming = optarg;
> >                  break;
> >              case QEMU_OPTION_only_migratable:
> > -                /*
> > -                 * TODO: we can remove this option one day, and we
> > -                 * should all use:
> > -                 *
> > -                 * "-global migration.only-migratable=true"
> > -                 */
> > -                qemu_global_option("migration.only-migratable=true");
> > +                only_migratable = 1;
> >                  break;
> >              case QEMU_OPTION_nodefaults:
> >                  has_defaults = 0;
> > -- 
> > 2.17.2
> > 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> 

Regards,
Daniel
-- 
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Daniel P. Berrangé <berrange@redhat.com> writes:

> On Mon, Apr 01, 2019 at 10:27:49AM +0100, Dr. David Alan Gilbert wrote:
>> * Markus Armbruster (armbru@redhat.com) wrote:
>> > This reverts commit 3df663e575f1876d7f3bc684f80e72fca0703d39.
>> > This reverts commit b605c47b57b58e61a901a50a0762dccf43d94783.
>> > 
>> > Command line option --only-migratable is for disallowing any
>> > configuration that can block migration.
>> > 
>> > Initially, --only-migratable set global variable @only_migratable.
>> > 
>> > Commit 3df663e575 "migration: move only_migratable to MigrationState"
>> > replaced it by MigrationState member @only_migratable.  That was a
>> > mistake.
>> > 
>> > First, it doesn't make sense on the design level.  MigrationState
>> > captures the state of an individual migration, but --only-migratable
>> > isn't a property of an individual migration, it's a restriction on
>> > QEMU configuration.  With fault tolerance, we could have several
>> > migrations at once.  --only-migratable would certainly protect all of
>> > them.  Storing it in MigrationState feels inappropriate.
>> > 
>> > Second, it contributes to a dependency cycle that manifests itself as
>> > a bug now.
>> > 
>> > Putting @only_migratable into MigrationState means its available only
>> > after migration_object_init().
>> > 
>> > We can't set it before migration_object_init(), so we delay setting it
>> > with a global property (this is fixup commit b605c47b57 "migration:
>> > fix handling for --only-migratable").
>> > 
>> > We can't get it before migration_object_init(), so anything that uses
>> > it can only run afterwards.
>> > 
>> > Since migrate_add_blocker() needs to obey --only-migratable, any code
>> > adding migration blockers can run only afterwards.  This contributes
>> > to the following dependency cycle:
>> > 
>> > * configure_blockdev() must run before machine_set_property()
>> >   so machine properties can refer to block backends
>> > 
>> > * machine_set_property() before configure_accelerator()
>> >   so machine properties like kvm-irqchip get applied
>> > 
>> > * configure_accelerator() before migration_object_init()
>> >   so that Xen's accelerator compat properties get applied.
>> > 
>> > * migration_object_init() before configure_blockdev()
>> >   so configure_blockdev() can add migration blockers
>> > 
>> > The cycle was closed when recent commit cda4aa9a5a0 "Create block
>> > backends before setting machine properties" added the first
>> > dependency, and satisfied it by violating the last one.  Broke block
>> > backends that add migration blockers.
>> > 
>> > Moving @only_migratable into MigrationState was a mistake.  Revert it.
>> > 
>> > This doesn't quite break the "migration_object_init() before
>> > configure_blockdev() dependency, since migrate_add_blocker() still has
>> > another dependency on migration_object_init().  To be addressed the
>> > next commit
>> > 
>> > Conflicts:
>> > 	include/migration/misc.h
>> > 	migration/migration.c
>> > 	migration/migration.h
>> > 	vl.c
>> > 
>> > Signed-off-by: Markus Armbruster <armbru@redhat.com>
>> > ---
>> >  include/sysemu/sysemu.h | 1 +
>> >  migration/migration.c   | 5 ++---
>> >  migration/migration.h   | 3 ---
>> >  migration/savevm.c      | 2 +-
>> >  vl.c                    | 9 ++-------
>> >  5 files changed, 6 insertions(+), 14 deletions(-)
>> > 
>> > diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
>> > index 6065d9e420..5f133cae83 100644
>> > --- a/include/sysemu/sysemu.h
>> > +++ b/include/sysemu/sysemu.h
>> > @@ -14,6 +14,7 @@
>> >  /* vl.c */
>> >  
>> >  extern const char *bios_name;
>> > +extern int only_migratable;
>> >  extern const char *qemu_name;
>> >  extern QemuUUID qemu_uuid;
>> >  extern bool qemu_uuid_set;
>> > diff --git a/migration/migration.c b/migration/migration.c
>> > index 69f75124c9..f6076e5295 100644
>> > --- a/migration/migration.c
>> > +++ b/migration/migration.c
>> > @@ -1707,7 +1707,7 @@ static GSList *migration_blockers;
>> >  
>> >  int migrate_add_blocker(Error *reason, Error **errp)
>> >  {
>> > -    if (migrate_get_current()->only_migratable) {
>> > +    if (only_migratable) {
>> >          error_propagate_prepend(errp, error_copy(reason),
>> >                                  "disallowing migration blocker "
>> >                                  "(--only_migratable) for: ");
>> > @@ -3337,7 +3337,7 @@ void migration_global_dump(Monitor *mon)
>> >      monitor_printf(mon, "store-global-state: %s\n",
>> >                     ms->store_global_state ? "on" : "off");
>> >      monitor_printf(mon, "only-migratable: %s\n",
>> > -                   ms->only_migratable ? "on" : "off");
>> > +                   only_migratable ? "on" : "off");
>> >      monitor_printf(mon, "send-configuration: %s\n",
>> >                     ms->send_configuration ? "on" : "off");
>> >      monitor_printf(mon, "send-section-footer: %s\n",
>> > @@ -3352,7 +3352,6 @@ void migration_global_dump(Monitor *mon)
>> >  static Property migration_properties[] = {
>> >      DEFINE_PROP_BOOL("store-global-state", MigrationState,
>> >                       store_global_state, true),
>> > -    DEFINE_PROP_BOOL("only-migratable", MigrationState, only_migratable, false),
>> 
>> So I'm generally OK at this patch, but I'm worried whether this
>> is API?

Uh, forgot to discuss this in my commit message, sorry!

> IIUC, old code can use either
>
>   -global migration.only-migratable=true
>   -only-migratable
>
> After this patch only
>
>   -only-migratable
>
> is valid. So from that POV it is an API break. 
>
> From libvirt's POV this is a non-issue as we never use either of these options.
> We did have a BZ filed to support it, but never did.
>
> To avoid the API break I guess there would been to be a special case early
> loop iterating over argv[] looking for '-global migration.only-migratable=true',
> making that set the static 'bool only_migratable', instead of letting it get
> handled by the object infra.

Is this is worth the trouble?

-global migration.only-migratable=on is entirely undocumented.  The
property appears in -device migration,help and device-list-properties,
but that's all.

Why would any sane person risk using arcane & undocumented -global
migration.only-migratable=on instead of the obvious & documented
-only-migratable?

[...]

On Mon, Apr 01, 2019 at 01:31:47PM +0200, Markus Armbruster wrote:
> Daniel P. Berrangé <berrange@redhat.com> writes:
> 
> > On Mon, Apr 01, 2019 at 10:27:49AM +0100, Dr. David Alan Gilbert wrote:
> >> * Markus Armbruster (armbru@redhat.com) wrote:
> >> > This reverts commit 3df663e575f1876d7f3bc684f80e72fca0703d39.
> >> > This reverts commit b605c47b57b58e61a901a50a0762dccf43d94783.
> >> > 
> >> > Command line option --only-migratable is for disallowing any
> >> > configuration that can block migration.
> >> > 
> >> > Initially, --only-migratable set global variable @only_migratable.
> >> > 
> >> > Commit 3df663e575 "migration: move only_migratable to MigrationState"
> >> > replaced it by MigrationState member @only_migratable.  That was a
> >> > mistake.
> >> > 
> >> > First, it doesn't make sense on the design level.  MigrationState
> >> > captures the state of an individual migration, but --only-migratable
> >> > isn't a property of an individual migration, it's a restriction on
> >> > QEMU configuration.  With fault tolerance, we could have several
> >> > migrations at once.  --only-migratable would certainly protect all of
> >> > them.  Storing it in MigrationState feels inappropriate.
> >> > 
> >> > Second, it contributes to a dependency cycle that manifests itself as
> >> > a bug now.
> >> > 
> >> > Putting @only_migratable into MigrationState means its available only
> >> > after migration_object_init().
> >> > 
> >> > We can't set it before migration_object_init(), so we delay setting it
> >> > with a global property (this is fixup commit b605c47b57 "migration:
> >> > fix handling for --only-migratable").
> >> > 
> >> > We can't get it before migration_object_init(), so anything that uses
> >> > it can only run afterwards.
> >> > 
> >> > Since migrate_add_blocker() needs to obey --only-migratable, any code
> >> > adding migration blockers can run only afterwards.  This contributes
> >> > to the following dependency cycle:
> >> > 
> >> > * configure_blockdev() must run before machine_set_property()
> >> >   so machine properties can refer to block backends
> >> > 
> >> > * machine_set_property() before configure_accelerator()
> >> >   so machine properties like kvm-irqchip get applied
> >> > 
> >> > * configure_accelerator() before migration_object_init()
> >> >   so that Xen's accelerator compat properties get applied.
> >> > 
> >> > * migration_object_init() before configure_blockdev()
> >> >   so configure_blockdev() can add migration blockers
> >> > 
> >> > The cycle was closed when recent commit cda4aa9a5a0 "Create block
> >> > backends before setting machine properties" added the first
> >> > dependency, and satisfied it by violating the last one.  Broke block
> >> > backends that add migration blockers.
> >> > 
> >> > Moving @only_migratable into MigrationState was a mistake.  Revert it.
> >> > 
> >> > This doesn't quite break the "migration_object_init() before
> >> > configure_blockdev() dependency, since migrate_add_blocker() still has
> >> > another dependency on migration_object_init().  To be addressed the
> >> > next commit
> >> > 
> >> > Conflicts:
> >> > 	include/migration/misc.h
> >> > 	migration/migration.c
> >> > 	migration/migration.h
> >> > 	vl.c
> >> > 
> >> > Signed-off-by: Markus Armbruster <armbru@redhat.com>
> >> > ---
> >> >  include/sysemu/sysemu.h | 1 +
> >> >  migration/migration.c   | 5 ++---
> >> >  migration/migration.h   | 3 ---
> >> >  migration/savevm.c      | 2 +-
> >> >  vl.c                    | 9 ++-------
> >> >  5 files changed, 6 insertions(+), 14 deletions(-)
> >> > 
> >> > diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> >> > index 6065d9e420..5f133cae83 100644
> >> > --- a/include/sysemu/sysemu.h
> >> > +++ b/include/sysemu/sysemu.h
> >> > @@ -14,6 +14,7 @@
> >> >  /* vl.c */
> >> >  
> >> >  extern const char *bios_name;
> >> > +extern int only_migratable;
> >> >  extern const char *qemu_name;
> >> >  extern QemuUUID qemu_uuid;
> >> >  extern bool qemu_uuid_set;
> >> > diff --git a/migration/migration.c b/migration/migration.c
> >> > index 69f75124c9..f6076e5295 100644
> >> > --- a/migration/migration.c
> >> > +++ b/migration/migration.c
> >> > @@ -1707,7 +1707,7 @@ static GSList *migration_blockers;
> >> >  
> >> >  int migrate_add_blocker(Error *reason, Error **errp)
> >> >  {
> >> > -    if (migrate_get_current()->only_migratable) {
> >> > +    if (only_migratable) {
> >> >          error_propagate_prepend(errp, error_copy(reason),
> >> >                                  "disallowing migration blocker "
> >> >                                  "(--only_migratable) for: ");
> >> > @@ -3337,7 +3337,7 @@ void migration_global_dump(Monitor *mon)
> >> >      monitor_printf(mon, "store-global-state: %s\n",
> >> >                     ms->store_global_state ? "on" : "off");
> >> >      monitor_printf(mon, "only-migratable: %s\n",
> >> > -                   ms->only_migratable ? "on" : "off");
> >> > +                   only_migratable ? "on" : "off");
> >> >      monitor_printf(mon, "send-configuration: %s\n",
> >> >                     ms->send_configuration ? "on" : "off");
> >> >      monitor_printf(mon, "send-section-footer: %s\n",
> >> > @@ -3352,7 +3352,6 @@ void migration_global_dump(Monitor *mon)
> >> >  static Property migration_properties[] = {
> >> >      DEFINE_PROP_BOOL("store-global-state", MigrationState,
> >> >                       store_global_state, true),
> >> > -    DEFINE_PROP_BOOL("only-migratable", MigrationState, only_migratable, false),
> >> 
> >> So I'm generally OK at this patch, but I'm worried whether this
> >> is API?
> 
> Uh, forgot to discuss this in my commit message, sorry!
> 
> > IIUC, old code can use either
> >
> >   -global migration.only-migratable=true
> >   -only-migratable
> >
> > After this patch only
> >
> >   -only-migratable
> >
> > is valid. So from that POV it is an API break. 
> >
> > From libvirt's POV this is a non-issue as we never use either of these options.
> > We did have a BZ filed to support it, but never did.
> >
> > To avoid the API break I guess there would been to be a special case early
> > loop iterating over argv[] looking for '-global migration.only-migratable=true',
> > making that set the static 'bool only_migratable', instead of letting it get
> > handled by the object infra.
> 
> Is this is worth the trouble?

Probably not.

> -global migration.only-migratable=on is entirely undocumented.  The
> property appears in -device migration,help and device-list-properties,
> but that's all.
> 
> Why would any sane person risk using arcane & undocumented -global
> migration.only-migratable=on instead of the obvious & documented
> -only-migratable?

Given the combination of no known users, current broken impl, and its
existance not documented, I think there's a reasonable case for just
removing it.

Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|

* Daniel P. Berrangé (berrange@redhat.com) wrote:
> On Mon, Apr 01, 2019 at 01:31:47PM +0200, Markus Armbruster wrote:
> > Daniel P. Berrangé <berrange@redhat.com> writes:
> > 
> > > On Mon, Apr 01, 2019 at 10:27:49AM +0100, Dr. David Alan Gilbert wrote:
> > >> * Markus Armbruster (armbru@redhat.com) wrote:
> > >> > This reverts commit 3df663e575f1876d7f3bc684f80e72fca0703d39.
> > >> > This reverts commit b605c47b57b58e61a901a50a0762dccf43d94783.
> > >> > 
> > >> > Command line option --only-migratable is for disallowing any
> > >> > configuration that can block migration.
> > >> > 
> > >> > Initially, --only-migratable set global variable @only_migratable.
> > >> > 
> > >> > Commit 3df663e575 "migration: move only_migratable to MigrationState"
> > >> > replaced it by MigrationState member @only_migratable.  That was a
> > >> > mistake.
> > >> > 
> > >> > First, it doesn't make sense on the design level.  MigrationState
> > >> > captures the state of an individual migration, but --only-migratable
> > >> > isn't a property of an individual migration, it's a restriction on
> > >> > QEMU configuration.  With fault tolerance, we could have several
> > >> > migrations at once.  --only-migratable would certainly protect all of
> > >> > them.  Storing it in MigrationState feels inappropriate.
> > >> > 
> > >> > Second, it contributes to a dependency cycle that manifests itself as
> > >> > a bug now.
> > >> > 
> > >> > Putting @only_migratable into MigrationState means its available only
> > >> > after migration_object_init().
> > >> > 
> > >> > We can't set it before migration_object_init(), so we delay setting it
> > >> > with a global property (this is fixup commit b605c47b57 "migration:
> > >> > fix handling for --only-migratable").
> > >> > 
> > >> > We can't get it before migration_object_init(), so anything that uses
> > >> > it can only run afterwards.
> > >> > 
> > >> > Since migrate_add_blocker() needs to obey --only-migratable, any code
> > >> > adding migration blockers can run only afterwards.  This contributes
> > >> > to the following dependency cycle:
> > >> > 
> > >> > * configure_blockdev() must run before machine_set_property()
> > >> >   so machine properties can refer to block backends
> > >> > 
> > >> > * machine_set_property() before configure_accelerator()
> > >> >   so machine properties like kvm-irqchip get applied
> > >> > 
> > >> > * configure_accelerator() before migration_object_init()
> > >> >   so that Xen's accelerator compat properties get applied.
> > >> > 
> > >> > * migration_object_init() before configure_blockdev()
> > >> >   so configure_blockdev() can add migration blockers
> > >> > 
> > >> > The cycle was closed when recent commit cda4aa9a5a0 "Create block
> > >> > backends before setting machine properties" added the first
> > >> > dependency, and satisfied it by violating the last one.  Broke block
> > >> > backends that add migration blockers.
> > >> > 
> > >> > Moving @only_migratable into MigrationState was a mistake.  Revert it.
> > >> > 
> > >> > This doesn't quite break the "migration_object_init() before
> > >> > configure_blockdev() dependency, since migrate_add_blocker() still has
> > >> > another dependency on migration_object_init().  To be addressed the
> > >> > next commit
> > >> > 
> > >> > Conflicts:
> > >> > 	include/migration/misc.h
> > >> > 	migration/migration.c
> > >> > 	migration/migration.h
> > >> > 	vl.c
> > >> > 
> > >> > Signed-off-by: Markus Armbruster <armbru@redhat.com>
> > >> > ---
> > >> >  include/sysemu/sysemu.h | 1 +
> > >> >  migration/migration.c   | 5 ++---
> > >> >  migration/migration.h   | 3 ---
> > >> >  migration/savevm.c      | 2 +-
> > >> >  vl.c                    | 9 ++-------
> > >> >  5 files changed, 6 insertions(+), 14 deletions(-)
> > >> > 
> > >> > diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> > >> > index 6065d9e420..5f133cae83 100644
> > >> > --- a/include/sysemu/sysemu.h
> > >> > +++ b/include/sysemu/sysemu.h
> > >> > @@ -14,6 +14,7 @@
> > >> >  /* vl.c */
> > >> >  
> > >> >  extern const char *bios_name;
> > >> > +extern int only_migratable;
> > >> >  extern const char *qemu_name;
> > >> >  extern QemuUUID qemu_uuid;
> > >> >  extern bool qemu_uuid_set;
> > >> > diff --git a/migration/migration.c b/migration/migration.c
> > >> > index 69f75124c9..f6076e5295 100644
> > >> > --- a/migration/migration.c
> > >> > +++ b/migration/migration.c
> > >> > @@ -1707,7 +1707,7 @@ static GSList *migration_blockers;
> > >> >  
> > >> >  int migrate_add_blocker(Error *reason, Error **errp)
> > >> >  {
> > >> > -    if (migrate_get_current()->only_migratable) {
> > >> > +    if (only_migratable) {
> > >> >          error_propagate_prepend(errp, error_copy(reason),
> > >> >                                  "disallowing migration blocker "
> > >> >                                  "(--only_migratable) for: ");
> > >> > @@ -3337,7 +3337,7 @@ void migration_global_dump(Monitor *mon)
> > >> >      monitor_printf(mon, "store-global-state: %s\n",
> > >> >                     ms->store_global_state ? "on" : "off");
> > >> >      monitor_printf(mon, "only-migratable: %s\n",
> > >> > -                   ms->only_migratable ? "on" : "off");
> > >> > +                   only_migratable ? "on" : "off");
> > >> >      monitor_printf(mon, "send-configuration: %s\n",
> > >> >                     ms->send_configuration ? "on" : "off");
> > >> >      monitor_printf(mon, "send-section-footer: %s\n",
> > >> > @@ -3352,7 +3352,6 @@ void migration_global_dump(Monitor *mon)
> > >> >  static Property migration_properties[] = {
> > >> >      DEFINE_PROP_BOOL("store-global-state", MigrationState,
> > >> >                       store_global_state, true),
> > >> > -    DEFINE_PROP_BOOL("only-migratable", MigrationState, only_migratable, false),
> > >> 
> > >> So I'm generally OK at this patch, but I'm worried whether this
> > >> is API?
> > 
> > Uh, forgot to discuss this in my commit message, sorry!
> > 
> > > IIUC, old code can use either
> > >
> > >   -global migration.only-migratable=true
> > >   -only-migratable
> > >
> > > After this patch only
> > >
> > >   -only-migratable
> > >
> > > is valid. So from that POV it is an API break. 
> > >
> > > From libvirt's POV this is a non-issue as we never use either of these options.
> > > We did have a BZ filed to support it, but never did.
> > >
> > > To avoid the API break I guess there would been to be a special case early
> > > loop iterating over argv[] looking for '-global migration.only-migratable=true',
> > > making that set the static 'bool only_migratable', instead of letting it get
> > > handled by the object infra.
> > 
> > Is this is worth the trouble?
> 
> Probably not.
> 
> > -global migration.only-migratable=on is entirely undocumented.  The
> > property appears in -device migration,help and device-list-properties,
> > but that's all.
> > 
> > Why would any sane person risk using arcane & undocumented -global
> > migration.only-migratable=on instead of the obvious & documented
> > -only-migratable?
> 
> Given the combination of no known users, current broken impl, and its
> existance not documented, I think there's a reasonable case for just
> removing it.

Yes, agreed - it should be noted though.

Dave

> Regards,
> Daniel
> -- 
> |: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
> |: https://libvirt.org         -o-            https://fstop138.berrange.com :|
> |: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

On Mon,  1 Apr 2019 11:08:24 +0200
Markus Armbruster <armbru@redhat.com> wrote:

> This reverts commit 3df663e575f1876d7f3bc684f80e72fca0703d39.
> This reverts commit b605c47b57b58e61a901a50a0762dccf43d94783.
> 
> Command line option --only-migratable is for disallowing any
> configuration that can block migration.
> 
> Initially, --only-migratable set global variable @only_migratable.
> 
> Commit 3df663e575 "migration: move only_migratable to MigrationState"
> replaced it by MigrationState member @only_migratable.  That was a
> mistake.
> 
> First, it doesn't make sense on the design level.  MigrationState
> captures the state of an individual migration, but --only-migratable
> isn't a property of an individual migration, it's a restriction on
> QEMU configuration.  With fault tolerance, we could have several
> migrations at once.  --only-migratable would certainly protect all of
> them.  Storing it in MigrationState feels inappropriate.
> 
> Second, it contributes to a dependency cycle that manifests itself as
> a bug now.
> 
> Putting @only_migratable into MigrationState means its available only
> after migration_object_init().
> 
> We can't set it before migration_object_init(), so we delay setting it
> with a global property (this is fixup commit b605c47b57 "migration:
> fix handling for --only-migratable").
> 
> We can't get it before migration_object_init(), so anything that uses
> it can only run afterwards.
> 
> Since migrate_add_blocker() needs to obey --only-migratable, any code
> adding migration blockers can run only afterwards.  This contributes
> to the following dependency cycle:
> 
> * configure_blockdev() must run before machine_set_property()
>   so machine properties can refer to block backends
> 
> * machine_set_property() before configure_accelerator()
>   so machine properties like kvm-irqchip get applied
> 
> * configure_accelerator() before migration_object_init()
>   so that Xen's accelerator compat properties get applied.
> 
> * migration_object_init() before configure_blockdev()
>   so configure_blockdev() can add migration blockers
> 
> The cycle was closed when recent commit cda4aa9a5a0 "Create block
> backends before setting machine properties" added the first
> dependency, and satisfied it by violating the last one.  Broke block
> backends that add migration blockers.
> 
> Moving @only_migratable into MigrationState was a mistake.  Revert it.
> 
> This doesn't quite break the "migration_object_init() before
> configure_blockdev() dependency, since migrate_add_blocker() still has
> another dependency on migration_object_init().  To be addressed the
> next commit
> 
> Conflicts:
> 	include/migration/misc.h
> 	migration/migration.c
> 	migration/migration.h
> 	vl.c
> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>

with commit message amended like mentioned by David
(wrt removed "only-migratable" property)

Reviewed-by: Igor Mammedov <imammedo@redhat.com>

> ---
>  include/sysemu/sysemu.h | 1 +
>  migration/migration.c   | 5 ++---
>  migration/migration.h   | 3 ---
>  migration/savevm.c      | 2 +-
>  vl.c                    | 9 ++-------
>  5 files changed, 6 insertions(+), 14 deletions(-)
> 
> diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> index 6065d9e420..5f133cae83 100644
> --- a/include/sysemu/sysemu.h
> +++ b/include/sysemu/sysemu.h
> @@ -14,6 +14,7 @@
>  /* vl.c */
>  
>  extern const char *bios_name;
> +extern int only_migratable;
>  extern const char *qemu_name;
>  extern QemuUUID qemu_uuid;
>  extern bool qemu_uuid_set;
> diff --git a/migration/migration.c b/migration/migration.c
> index 69f75124c9..f6076e5295 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1707,7 +1707,7 @@ static GSList *migration_blockers;
>  
>  int migrate_add_blocker(Error *reason, Error **errp)
>  {
> -    if (migrate_get_current()->only_migratable) {
> +    if (only_migratable) {
>          error_propagate_prepend(errp, error_copy(reason),
>                                  "disallowing migration blocker "
>                                  "(--only_migratable) for: ");
> @@ -3337,7 +3337,7 @@ void migration_global_dump(Monitor *mon)
>      monitor_printf(mon, "store-global-state: %s\n",
>                     ms->store_global_state ? "on" : "off");
>      monitor_printf(mon, "only-migratable: %s\n",
> -                   ms->only_migratable ? "on" : "off");
> +                   only_migratable ? "on" : "off");
>      monitor_printf(mon, "send-configuration: %s\n",
>                     ms->send_configuration ? "on" : "off");
>      monitor_printf(mon, "send-section-footer: %s\n",
> @@ -3352,7 +3352,6 @@ void migration_global_dump(Monitor *mon)
>  static Property migration_properties[] = {
>      DEFINE_PROP_BOOL("store-global-state", MigrationState,
>                       store_global_state, true),
> -    DEFINE_PROP_BOOL("only-migratable", MigrationState, only_migratable, false),
>      DEFINE_PROP_BOOL("send-configuration", MigrationState,
>                       send_configuration, true),
>      DEFINE_PROP_BOOL("send-section-footer", MigrationState,
> diff --git a/migration/migration.h b/migration/migration.h
> index 0f986935e1..438f17edad 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -219,9 +219,6 @@ struct MigrationState
>       */
>      bool store_global_state;
>  
> -    /* Whether the VM is only allowing for migratable devices */
> -    bool only_migratable;
> -
>      /* Whether we send QEMU_VM_CONFIGURATION during migration */
>      bool send_configuration;
>      /* Whether we send section footer during migration */
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 1415001d1c..34bcad3807 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -2844,7 +2844,7 @@ void vmstate_register_ram_global(MemoryRegion *mr)
>  bool vmstate_check_only_migratable(const VMStateDescription *vmsd)
>  {
>      /* check needed if --only-migratable is specified */
> -    if (!migrate_get_current()->only_migratable) {
> +    if (!only_migratable) {
>          return true;
>      }
>  
> diff --git a/vl.c b/vl.c
> index c1d5484e12..e4d7ad6b85 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -185,6 +185,7 @@ const char *prom_envs[MAX_PROM_ENVS];
>  int boot_menu;
>  bool boot_strict;
>  uint8_t *boot_splash_filedata;
> +int only_migratable; /* turn it off unless user states otherwise */
>  bool wakeup_suspend_enabled;
>  
>  int icount_align_option;
> @@ -3799,13 +3800,7 @@ int main(int argc, char **argv, char **envp)
>                  incoming = optarg;
>                  break;
>              case QEMU_OPTION_only_migratable:
> -                /*
> -                 * TODO: we can remove this option one day, and we
> -                 * should all use:
> -                 *
> -                 * "-global migration.only-migratable=true"
> -                 */
> -                qemu_global_option("migration.only-migratable=true");
> +                only_migratable = 1;
>                  break;
>              case QEMU_OPTION_nodefaults:
>                  has_defaults = 0;

Igor Mammedov <imammedo@redhat.com> writes:

> On Mon,  1 Apr 2019 11:08:24 +0200
> Markus Armbruster <armbru@redhat.com> wrote:
>
>> This reverts commit 3df663e575f1876d7f3bc684f80e72fca0703d39.
>> This reverts commit b605c47b57b58e61a901a50a0762dccf43d94783.
>> 
>> Command line option --only-migratable is for disallowing any
>> configuration that can block migration.
>> 
>> Initially, --only-migratable set global variable @only_migratable.
>> 
>> Commit 3df663e575 "migration: move only_migratable to MigrationState"
>> replaced it by MigrationState member @only_migratable.  That was a
>> mistake.
>> 
>> First, it doesn't make sense on the design level.  MigrationState
>> captures the state of an individual migration, but --only-migratable
>> isn't a property of an individual migration, it's a restriction on
>> QEMU configuration.  With fault tolerance, we could have several
>> migrations at once.  --only-migratable would certainly protect all of
>> them.  Storing it in MigrationState feels inappropriate.
>> 
>> Second, it contributes to a dependency cycle that manifests itself as
>> a bug now.
>> 
>> Putting @only_migratable into MigrationState means its available only
>> after migration_object_init().
>> 
>> We can't set it before migration_object_init(), so we delay setting it
>> with a global property (this is fixup commit b605c47b57 "migration:
>> fix handling for --only-migratable").
>> 
>> We can't get it before migration_object_init(), so anything that uses
>> it can only run afterwards.
>> 
>> Since migrate_add_blocker() needs to obey --only-migratable, any code
>> adding migration blockers can run only afterwards.  This contributes
>> to the following dependency cycle:
>> 
>> * configure_blockdev() must run before machine_set_property()
>>   so machine properties can refer to block backends
>> 
>> * machine_set_property() before configure_accelerator()
>>   so machine properties like kvm-irqchip get applied
>> 
>> * configure_accelerator() before migration_object_init()
>>   so that Xen's accelerator compat properties get applied.
>> 
>> * migration_object_init() before configure_blockdev()
>>   so configure_blockdev() can add migration blockers
>> 
>> The cycle was closed when recent commit cda4aa9a5a0 "Create block
>> backends before setting machine properties" added the first
>> dependency, and satisfied it by violating the last one.  Broke block
>> backends that add migration blockers.
>> 
>> Moving @only_migratable into MigrationState was a mistake.  Revert it.
>> 
>> This doesn't quite break the "migration_object_init() before
>> configure_blockdev() dependency, since migrate_add_blocker() still has
>> another dependency on migration_object_init().  To be addressed the
>> next commit
>> 
>> Conflicts:
>> 	include/migration/misc.h
>> 	migration/migration.c
>> 	migration/migration.h
>> 	vl.c
>> 
>> Signed-off-by: Markus Armbruster <armbru@redhat.com>
>
> with commit message amended like mentioned by David
> (wrt removed "only-migratable" property)

Inserting right before the "Conflicts:" line:

    Note that the reverted commit made -only-migratable sugar for -global
    migration.only-migratable=on below the hood.  Documentation has only
    ever mentioned -only-migratable.  This commit removes the arcane &
    undocumented alternative to -only-migratable again.  Nobody should be
    using it.

> Reviewed-by: Igor Mammedov <imammedo@redhat.com>

Thanks!

* Markus Armbruster (armbru@redhat.com) wrote:
> Igor Mammedov <imammedo@redhat.com> writes:
> 
> > On Mon,  1 Apr 2019 11:08:24 +0200
> > Markus Armbruster <armbru@redhat.com> wrote:
> >
> >> This reverts commit 3df663e575f1876d7f3bc684f80e72fca0703d39.
> >> This reverts commit b605c47b57b58e61a901a50a0762dccf43d94783.
> >> 
> >> Command line option --only-migratable is for disallowing any
> >> configuration that can block migration.
> >> 
> >> Initially, --only-migratable set global variable @only_migratable.
> >> 
> >> Commit 3df663e575 "migration: move only_migratable to MigrationState"
> >> replaced it by MigrationState member @only_migratable.  That was a
> >> mistake.
> >> 
> >> First, it doesn't make sense on the design level.  MigrationState
> >> captures the state of an individual migration, but --only-migratable
> >> isn't a property of an individual migration, it's a restriction on
> >> QEMU configuration.  With fault tolerance, we could have several
> >> migrations at once.  --only-migratable would certainly protect all of
> >> them.  Storing it in MigrationState feels inappropriate.
> >> 
> >> Second, it contributes to a dependency cycle that manifests itself as
> >> a bug now.
> >> 
> >> Putting @only_migratable into MigrationState means its available only
> >> after migration_object_init().
> >> 
> >> We can't set it before migration_object_init(), so we delay setting it
> >> with a global property (this is fixup commit b605c47b57 "migration:
> >> fix handling for --only-migratable").
> >> 
> >> We can't get it before migration_object_init(), so anything that uses
> >> it can only run afterwards.
> >> 
> >> Since migrate_add_blocker() needs to obey --only-migratable, any code
> >> adding migration blockers can run only afterwards.  This contributes
> >> to the following dependency cycle:
> >> 
> >> * configure_blockdev() must run before machine_set_property()
> >>   so machine properties can refer to block backends
> >> 
> >> * machine_set_property() before configure_accelerator()
> >>   so machine properties like kvm-irqchip get applied
> >> 
> >> * configure_accelerator() before migration_object_init()
> >>   so that Xen's accelerator compat properties get applied.
> >> 
> >> * migration_object_init() before configure_blockdev()
> >>   so configure_blockdev() can add migration blockers
> >> 
> >> The cycle was closed when recent commit cda4aa9a5a0 "Create block
> >> backends before setting machine properties" added the first
> >> dependency, and satisfied it by violating the last one.  Broke block
> >> backends that add migration blockers.
> >> 
> >> Moving @only_migratable into MigrationState was a mistake.  Revert it.
> >> 
> >> This doesn't quite break the "migration_object_init() before
> >> configure_blockdev() dependency, since migrate_add_blocker() still has
> >> another dependency on migration_object_init().  To be addressed the
> >> next commit
> >> 
> >> Conflicts:
> >> 	include/migration/misc.h
> >> 	migration/migration.c
> >> 	migration/migration.h
> >> 	vl.c
> >> 
> >> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> >
> > with commit message amended like mentioned by David
> > (wrt removed "only-migratable" property)
> 
> Inserting right before the "Conflicts:" line:
> 
>     Note that the reverted commit made -only-migratable sugar for -global
>     migration.only-migratable=on below the hood.  Documentation has only
>     ever mentioned -only-migratable.  This commit removes the arcane &
>     undocumented alternative to -only-migratable again.  Nobody should be
>     using it.

Yes, that's fine:

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> > Reviewed-by: Igor Mammedov <imammedo@redhat.com>
> 
> Thanks!
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK