Commit b17fbbe5 authored by Peng Tao's avatar Peng Tao Committed by Juan Quintela
Browse files

migration: allow private destination ram with x-ignore-shared 

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: default avatarPeng Tao <tao.peng@linux.alibaba.com>
Reviewed-by: default avatarJuan Quintela <quintela@redhat.com>
Reviewed-by: default avatarDr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <1560494113-1141-1-git-send-email-tao.peng@linux.alibaba.com>
Signed-off-by: default avatarJuan Quintela <quintela@redhat.com>
parent 002cad6b

migration/ram.c

+0 −7
Original line number Diff line number Diff line
@@ -3426,7 +3426,6 @@ 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);

        }

    }
@@ -4393,12 +4392,6 @@ 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 "