Re: [Qemu-devel] [PATCH] migration: allow private destination ram with x-ignore-shared

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Dr. David Alan Gilbert (dgilbert@redhat.com) wrote:
> * Peng Tao (tao.peng@linux.alibaba.com) wrote:
> > By removing the share ram check, qemu is able to migrate
> > to private destination ram when x-ignore-shared capability
> > is on. Then we can create multiple destination VMs based
> > on the same source VM.
> > 
> > This changes the x-ignore-shared migration capability to
> > work similar to Lai's original bypass-shared-memory
> > work(https://lists.gnu.org/archive/html/qemu-devel/2018-04/msg00003.html)
> > which enables kata containers (https://katacontainers.io)
> > to implement the VM templating feature.
> > 
> > An example usage in kata containers(https://katacontainers.io):
> > 1. Start the source VM:
> >    qemu-system-x86 -m 2G \
> >      -object memory-backend-file,id=mem0,size=2G,share=on,mem-path=/tmpfs/template-memory \
> >      -numa node,memdev=mem0
> > 2. Stop the template VM, set migration x-ignore-shared capability,
> >    migrate "exec:cat>/tmpfs/state", quit it
> > 3. Start target VM:
> >    qemu-system-x86 -m 2G \
> >      -object memory-backend-file,id=mem0,size=2G,share=off,mem-path=/tmpfs/template-memory \
> >      -numa node,memdev=mem0 \
> >      -incoming defer
> > 4. connect to target VM qmp, set migration x-ignore-shared capability,
> > migrate_incoming "exec:cat /tmpfs/state"
> > 5. create more target VMs repeating 3 and 4
> > 
> > Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > Cc: Yury Kotov <yury-kotov@yandex-team.ru>
> > Cc: Jiangshan Lai <laijs@hyper.sh>
> > Cc: Xu Wang <xu@hyper.sh>
> > Signed-off-by: Peng Tao <tao.peng@linux.alibaba.com>
> 
> I think this is OK, but please post this to qemu-devel.

Oh you did :-)  That's double fine then!

> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> 
> > ---
> >  migration/ram.c | 7 -------
> >  1 file changed, 7 deletions(-)
> > 
> > diff --git a/migration/ram.c b/migration/ram.c
> > index 1ca9ba7..cdb82a3 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -3373,7 +3373,6 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
> >          }
> >          if (migrate_ignore_shared()) {
> >              qemu_put_be64(f, block->mr->addr);
> > -            qemu_put_byte(f, ramblock_is_ignored(block) ? 1 : 0);
> >          }
> >      }
> >  
> > @@ -4340,12 +4339,6 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
> >                      }
> >                      if (migrate_ignore_shared()) {
> >                          hwaddr addr = qemu_get_be64(f);
> > -                        bool ignored = qemu_get_byte(f);
> > -                        if (ignored != ramblock_is_ignored(block)) {
> > -                            error_report("RAM block %s should %s be migrated",
> > -                                         id, ignored ? "" : "not");
> > -                            ret = -EINVAL;
> > -                        }
> >                          if (ramblock_is_ignored(block) &&
> >                              block->mr->addr != addr) {
> >                              error_report("Mismatched GPAs for block %s "
> > -- 
> > 1.8.3.1
> > 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK