Re: [Qemu-devel] [PATCH 2/3] migration: Test for disabled features on reception

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

* Juan Quintela (quintela@redhat.com) wrote:
> Right now, if we receive a compressed page or a xbzrle page while this
> features are disabled, Bad Things (TM) can happen.  Just add a test for
> them.

This confuses me; I didn't think until recently we could
guarantee anything about having the capabilities set on the destination
side.  Until -incoming defer the destination didn't have a way of setting
capabilities in a known state before starting the reception.

Dave

> Signed-off-by: Juan Quintela <quintela@redhat.com>
> ---
>  migration/ram.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index fb9252d..4bb707c 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -2464,7 +2464,7 @@ static int ram_load_postcopy(QEMUFile *f)
> 
>  static int ram_load(QEMUFile *f, void *opaque, int version_id)
>  {
> -    int flags = 0, ret = 0;
> +    int flags = 0, ret = 0, invalid_flags;
>      static uint64_t seq_iter;
>      int len = 0;
>      /*
> @@ -2479,6 +2479,15 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>          ret = -EINVAL;
>      }
> 
> +    invalid_flags = 0;
> +
> +    if (!migrate_use_xbzrle()) {
> +        invalid_flags |= RAM_SAVE_FLAG_XBZRLE;
> +    }
> +
> +    if (!migrate_use_compression()) {
> +        invalid_flags |= RAM_SAVE_FLAG_COMPRESS_PAGE;
> +    }
>      /* This RCU critical section can be very long running.
>       * When RCU reclaims in the code start to become numerous,
>       * it will be necessary to reduce the granularity of this
> @@ -2499,6 +2508,18 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>          flags = addr & ~TARGET_PAGE_MASK;
>          addr &= TARGET_PAGE_MASK;
> 
> +        if (flags & invalid_flags) {
> +            if (flags & invalid_flags  & RAM_SAVE_FLAG_XBZRLE) {
> +                error_report("Received an unexpected XBRLE page");
> +            }
> +            if (flags & invalid_flags  & RAM_SAVE_FLAG_COMPRESS_PAGE) {
> +                error_report("Received an unexpected compressed page");
> +            }
> +
> +            ret = -EINVAL;
> +            break;
> +        }
> +
>          if (flags & (RAM_SAVE_FLAG_COMPRESS | RAM_SAVE_FLAG_PAGE |
>                       RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE)) {
>              RAMBlock *block = ram_block_from_stream(f, flags);
> -- 
> 2.7.4
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK