netdev - Re: [PATCH net-next V2 2/3] xen-netback: avoid allocating variable size array on stack

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Message-Id: <5182726402000078000D2A24@nat28.tlf.novell.com>
Date:	Thu, 02 May 2013 13:04:20 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Wei Liu" <wei.liu2@...rix.com>
Cc:	<ian.campbell@...rix.com>, <xen-devel@...ts.xen.org>,
	<netdev@...r.kernel.org>
Subject: Re: [PATCH net-next V2 2/3] xen-netback: avoid allocating
 variable size array on stack

>>> On 02.05.13 at 12:43, Wei Liu <wei.liu2@...rix.com> wrote:
> @@ -934,11 +934,14 @@ static int netbk_count_requests(struct xenvif *vif,
>  	RING_IDX cons = vif->tx.req_cons;
>  	int slots = 0;
>  	int drop_err = 0;
> +	int more_data;
>  
>  	if (!(first->flags & XEN_NETTXF_more_data))
>  		return 0;
>  
>  	do {
> +		struct xen_netif_tx_request dropped_tx = { 0 };
> +

No need for an initializer here.

>  		if (slots >= work_to_do) {
>  			netdev_err(vif->dev,
>  				   "Asked for %d slots but exceeds this limit\n",
> @@ -972,6 +975,9 @@ static int netbk_count_requests(struct xenvif *vif,
>  			drop_err = -E2BIG;
>  		}
>  
> +		if (drop_err)
> +			txp = &dropped_tx;
> +
>  		memcpy(txp, RING_GET_REQUEST(&vif->tx, cons + slots),
>  		       sizeof(*txp));
>  
> @@ -1001,7 +1007,13 @@ static int netbk_count_requests(struct xenvif *vif,
>  			netbk_fatal_tx_err(vif);
>  			return -EINVAL;
>  		}
> -	} while ((txp++)->flags & XEN_NETTXF_more_data);
> +
> +		more_data = txp->flags & XEN_NETTXF_more_data;
> +
> +		if (!drop_err)
> +			txp++;

And no need for the conditional here afaict.

Jan

> +
> +	} while (more_data);
>  
>  	if (drop_err) {
>  		netbk_tx_err(vif, first, cons + slots);


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