On Sun, 2011-01-09 at 12:47 +0200, Michael S. Tsirkin wrote:
> On Fri, Jan 07, 2011 at 03:13:25PM -0700, Alex Williamson wrote:
> > The no_migrate save state flag is currently only checked in the
> > last phase of migration. This means that we potentially waste
> > a lot of time and bandwidth with the live state handlers before
> > we ever check the no_migrate flags. The error message printed
> > when we catch a non-migratable device doesn't get printed for
> > a detached migration. And, no_migrate does nothing to prevent
> > an incoming migration to a target that includes a non-migratable
> > device. This attempts to fix all of these.
> >
> > One notable difference in behavior is that an outgoing migration
> > now checks for non-migratable devices before ever connecting to
> > the target system. This means the target will remain listening
> > rather than exit from failure.
> >
> > Signed-off-by: Alex Williamson <alex.william...@redhat.com>
>
> Minor nit:
>
> The API of qemu_savevm_state_blocked is a bit strange.
> functions should either return 0/1 values or 0 on success
> negative on failure or a bool.
> This API asks "is it blocked" and returns -EINVAL to
> mean "yes". _blocked is also a bit ambigious:
> it seems to imply a temporary condition.
But it very well could be a temporary condition. If I have an assigned
device, it will block migration/savevm, but removing the device allows
it to proceed.
> How about we reverse the logic, call the new API
> qemu_savevm_state_supported, qemu_savevm_state_enabled,
> something like this?
> Then you can return 0 if migration is possible,
> -1 if not.
I tend to like qemu_savevm_state_blocked() as "supported" and "enabled"
invoke different ideas for me. I will concede that the errno return
value is a little awkward. How about if I make it a bool function
instead? Thanks,
Alex
> > ---
> >
> > v4:
> > - fix braces noted by Jan
> > - return error from qemu_savevm_state_blocked rather than fixed EINVAL
> > at qemu_loadvm_state(), since it'a already using errno values
> >
> > v3:
> >
> > Daniel, adding you to see if libvirt cares about the difference in
> > whether the target exits on migration failure as noted above.
> >
> > Also adding Michael as he's complained about the no_migrate check
> > happening so late in the process.
> >
> > migration.c | 4 ++++
> > savevm.c | 41 +++++++++++++++++++++++++++--------------
> > sysemu.h | 1 +
> > 3 files changed, 32 insertions(+), 14 deletions(-)
> >
> > diff --git a/migration.c b/migration.c
> > index e5ba51c..d593b1d 100644
> > --- a/migration.c
> > +++ b/migration.c
> > @@ -88,6 +88,10 @@ int do_migrate(Monitor *mon, const QDict *qdict, QObject
> > **ret_data)
> > return -1;
> > }
> >
> > + if (qemu_savevm_state_blocked(mon)) {
> > + return -1;
> > + }
> > +
> > if (strstart(uri, "tcp:", &p)) {
> > s = tcp_start_outgoing_migration(mon, p, max_throttle, detach,
> > blk, inc);
> > diff --git a/savevm.c b/savevm.c
> > index 90aa237..34c0d1a 100644
> > --- a/savevm.c
> > +++ b/savevm.c
> > @@ -1401,19 +1401,13 @@ static int vmstate_load(QEMUFile *f, SaveStateEntry
> > *se, int version_id)
> > return vmstate_load_state(f, se->vmsd, se->opaque, version_id);
> > }
> >
> > -static int vmstate_save(QEMUFile *f, SaveStateEntry *se)
> > +static void vmstate_save(QEMUFile *f, SaveStateEntry *se)
> > {
> > - if (se->no_migrate) {
> > - return -1;
> > - }
> > -
> > if (!se->vmsd) { /* Old style */
> > se->save_state(f, se->opaque);
> > - return 0;
> > + return;
> > }
> > vmstate_save_state(f,se->vmsd, se->opaque);
> > -
> > - return 0;
> > }
> >
> > #define QEMU_VM_FILE_MAGIC 0x5145564d
> > @@ -1427,6 +1421,20 @@ static int vmstate_save(QEMUFile *f, SaveStateEntry
> > *se)
> > #define QEMU_VM_SECTION_FULL 0x04
> > #define QEMU_VM_SUBSECTION 0x05
> >
> > +int qemu_savevm_state_blocked(Monitor *mon)
> > +{
> > + SaveStateEntry *se;
> > +
> > + QTAILQ_FOREACH(se, &savevm_handlers, entry) {
> > + if (se->no_migrate) {
> > + monitor_printf(mon, "state blocked by non-migratable device
> > '%s'\n",
> > + se->idstr);
> > + return -EINVAL;
> > + }
> > + }
> > + return 0;
> > +}
> > +
> > int qemu_savevm_state_begin(Monitor *mon, QEMUFile *f, int blk_enable,
> > int shared)
> > {
> > @@ -1508,7 +1516,6 @@ int qemu_savevm_state_iterate(Monitor *mon, QEMUFile
> > *f)
> > int qemu_savevm_state_complete(Monitor *mon, QEMUFile *f)
> > {
> > SaveStateEntry *se;
> > - int r;
> >
> > cpu_synchronize_all_states();
> >
> > @@ -1541,11 +1548,7 @@ int qemu_savevm_state_complete(Monitor *mon,
> > QEMUFile *f)
> > qemu_put_be32(f, se->instance_id);
> > qemu_put_be32(f, se->version_id);
> >
> > - r = vmstate_save(f, se);
> > - if (r < 0) {
> > - monitor_printf(mon, "cannot migrate with device '%s'\n",
> > se->idstr);
> > - return r;
> > - }
> > + vmstate_save(f, se);
> > }
> >
> > qemu_put_byte(f, QEMU_VM_EOF);
> > @@ -1575,6 +1578,11 @@ static int qemu_savevm_state(Monitor *mon, QEMUFile
> > *f)
> > saved_vm_running = vm_running;
> > vm_stop(0);
> >
> > + ret = qemu_savevm_state_blocked(mon);
> > + if (ret < 0) {
> > + goto out;
> > + }
> > +
> > ret = qemu_savevm_state_begin(mon, f, 0, 0);
> > if (ret < 0)
> > goto out;
> > @@ -1692,6 +1700,11 @@ int qemu_loadvm_state(QEMUFile *f)
> > unsigned int v;
> > int ret;
> >
> > + ret = qemu_savevm_state_blocked(default_mon);
> > + if (ret < 0) {
> > + return ret;
> > + }
> > +
> > v = qemu_get_be32(f);
> > if (v != QEMU_VM_FILE_MAGIC)
> > return -EINVAL;
> > diff --git a/sysemu.h b/sysemu.h
> > index e728ea1..eefaba5 100644
> > --- a/sysemu.h
> > +++ b/sysemu.h
> > @@ -75,6 +75,7 @@ void qemu_announce_self(void);
> >
> > void main_loop_wait(int nonblocking);
> >
> > +int qemu_savevm_state_blocked(Monitor *mon);
> > int qemu_savevm_state_begin(Monitor *mon, QEMUFile *f, int blk_enable,
> > int shared);
> > int qemu_savevm_state_iterate(Monitor *mon, QEMUFile *f);
