Re: [Qemu-devel] [PATCH v3 23/23] block: Make device model's references to BlockBackend strong

[Max Reitz]

On 16.09.2014 20:12, Markus Armbruster wrote:
> Doesn't make a difference just yet, but it's the right thing to do.
>
> Signed-off-by: Markus Armbruster <address@hidden>
> ---
>   block/block-backend.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/block/block-backend.c b/block/block-backend.c
> index d49c988..5646628 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -253,6 +253,7 @@ int blk_attach_dev(BlockBackend *blk, void *dev)
>       if (blk->dev) {
>           return -EBUSY;
>       }
> +    blk_ref(blk);
>       blk->dev = dev;
>       bdrv_iostatus_reset(blk->bs);
>   
> @@ -281,9 +282,10 @@ void blk_detach_dev(BlockBackend *blk, void *dev)
>   /* TODO change to DeviceState *dev when all users are qdevified */
>   {
>       assert(blk->dev == dev);
> -    blk->dev = NULL;
>       blk->dev_ops = NULL;
>       blk->dev_opaque = NULL;
> +    blk->dev = NULL;
> +    blk_unref(blk);
>       bdrv_set_guest_block_size(blk->bs, 512);
>       qemu_coroutine_adjust_pool_size(-COROUTINE_POOL_RESERVATION);
>   }

I'd put the blk_unref() call at the very end of this function. It 
probably won't happen but theoretically blk_unref() can free the 
BlockBackend object and I don't like the risk of use-after-free in blk->bs.

Max