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 --- 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 "