Re: [Qemu-devel] [RFC] exec: eliminate ram naming issue as migration

[Igor Mammedov <imammedo@redhat.com>]

On Mon,  5 Feb 2018 14:58:55 +0000
Jianfeng Tan <jianfeng.tan@intel.com> wrote:

> Existing VMs with virtio devices and vhost-kernel as the backend
> are always started with mem config:
> 
>   "-m xG"
>   (with a ram block named "pc.ram")
> 
> while new VMs with virtio devices and vhost-user as the backend
> are always started with mem config:
> 
>   "-m xG -numa node,memdev=pc.ram -object memory-backend-file,id=pc.ram,..."
>   (with a ram block named "/object/pc.ram")
could you elaborate more on what src command line migrating to what dst command line?


> As we migrate from vhost-kernel to vhost-user, it failes as:
> 
>   Unknown ramblock "pc.ram", cannot accept migration
>   error while loading state for instance 0x0 of device 'ram'
>   load of migration failed: Invalid argument
> 
> Here are some options to fix this:
> 
> 1. When we do ram name comparison, we truncate the prefix as this patch shows.
> It cannot cover the corner case: the source VM could have two ram blocks
> with name of "pc.ram" and "/object/pc.ram".
> 
> 2. We add an alias name to RAMBlock; when we do name comparison, not only
> idstr is compared, but also compared to the alias. But this will add more
> complexity to upper layer stack OpenStack/libvirt.
> 
> Any thoughts?
> 
> Cc: Jason Wang <jasowang@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
> ---
>  exec.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/exec.c b/exec.c
> index 4722e52..d294e5c 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2334,13 +2334,24 @@ found:
>  RAMBlock *qemu_ram_block_by_name(const char *name)
>  {
>      RAMBlock *block;
> +    char *name1, *id1;
> +    char *name2, *id2;
> +
> +    name1 = strdup(name);
> +    id1 = basename(name1);
>  
>      RAMBLOCK_FOREACH(block) {
> -        if (!strcmp(name, block->idstr)) {
> +        name2 = strdup(block->idstr);
> +	id2 = basename(name2);
> +        if (!strcmp(id1, id2)) {
> +            free(name1);
> +	    free(name2);
>              return block;
>          }
> +	free(name2);
>      }
>  
> +    free(name1);
>      return NULL;
>  }
>