Re: [Qemu-devel] [PATCH] hostmem-file: warn when memory-backend-file, share=on and in incoming migration

[Peter Xu <peterx@redhat.com>]

On Sun, Apr 07, 2019 at 10:19:05PM -0400, Catherine Ho wrote:
> Currently it is not forbidden to use "-object memory-backend-file,share=on"
> and together with "-incoming". But after incoming migration is finished,
> the memory-backend-file will be definitely written if share=on. So the
> memory-backend-file can only be used once, but failed in the 2nd time
> incoming.
> 
> Thus it gives a warning and the users can run the qemu if they really
> want to do it.
> 
> Signed-off-by: Catherine Ho <catherine.hecx@gmail.com>
> ---
>  backends/hostmem-file.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
> index 37ac6445d2..59429ee0b4 100644
> --- a/backends/hostmem-file.c
> +++ b/backends/hostmem-file.c
> @@ -16,6 +16,7 @@
>  #include "sysemu/hostmem.h"
>  #include "sysemu/sysemu.h"
>  #include "qom/object_interfaces.h"
> +#include "migration/migration.h"
>  
>  /* hostmem-file.c */
>  /**
> @@ -79,6 +80,16 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
>          }
>      }
>  
> +    /*
> +     * In ignore shared case, if share=on for host memory backend file,
> +     * the ram might be written after incoming process is finished. Thus
> +     * the memory backend can't be reused for 2nd/3rd... incoming
> +     */
> +    if (backend->share && migrate_ignore_shared()
> +                       && runstate_check(RUN_STATE_INMIGRATE))
> +        warn_report("share=on for memory backend file might be "
> +                        "conflicted with incoming in ignore shared case");

I feel like this message wasn't really clear to me...  you want to
warn people these data might not match with each other, right?  How
about simply state it:

  NOTE: Please make sure the data on the shared memory backend file
  and the data from the incoming migration stream contains matching
  contents, otherwise...

Regards,

-- 
Peter Xu