Re: [Qemu-devel] [PATCH 1/2] migration: bitmap_set is unnecessary as bitmap_new uses g_try_malloc0

[Wen Congyang]

On 09/25/2015 05:09 PM, Denis V. Lunev wrote:
> we can omit calling of bitmap_set in migration_bitmap_extend and
> ram_save_setup just after bitmap_new, which properly zeroes memory
> inside.

This patch is wrong. bitmap_set() is set all bits of the memory to 1,
not 0.

> 
> Signed-off-by: Denis V. Lunev <address@hidden>
> CC: Igor Redko <address@hidden>
> CC: Anna Melekhova <address@hidden>
> CC: Juan Quintela <address@hidden>
> CC: Amit Shah <address@hidden>
> CC: Wen Congyang <address@hidden>
> ---
>  migration/ram.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 7f007e6..a712c68 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1081,7 +1081,6 @@ void migration_bitmap_extend(ram_addr_t old, ram_addr_t 
> new)
>           */
>          qemu_mutex_lock(&migration_bitmap_mutex);
>          bitmap_copy(bitmap, old_bitmap, old);
> -        bitmap_set(bitmap, old, new - old);
>          atomic_rcu_set(&migration_bitmap, bitmap);
>          qemu_mutex_unlock(&migration_bitmap_mutex);
>          migration_dirty_pages += new - old;
> @@ -1146,7 +1145,6 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
>  
>      ram_bitmap_pages = last_ram_offset() >> TARGET_PAGE_BITS;
>      migration_bitmap = bitmap_new(ram_bitmap_pages);
> -    bitmap_set(migration_bitmap, 0, ram_bitmap_pages);
>  
>      /*
>       * Count the total number of pages used by ram blocks not including any
>