linux-kernel - Re: [PATCH] xen/netback: fix build warning

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Date:   Wed, 7 Dec 2022 10:25:26 +0100
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     Wei Liu <wei.liu@...nel.org>, Paul Durrant <paul@....org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, Ross Lagerwall <ross.lagerwall@...rix.com>
Subject: Re: [PATCH] xen/netback: fix build warning

On 07.12.2022 08:23, Juergen Gross wrote:
> Commit ad7f402ae4f4 ("xen/netback: Ensure protocol headers don't fall in
> the non-linear area") introduced a (valid) build warning.
> 
> Fix it.
> 
> Fixes: ad7f402ae4f4 ("xen/netback: Ensure protocol headers don't fall in the non-linear area")
> Signed-off-by: Juergen Gross <jgross@...e.com>

Reviewed-by: Jan Beulich <jbeulich@...e.com>

> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -530,7 +530,7 @@ static int xenvif_tx_check_gop(struct xenvif_queue *queue,
>  	const bool sharedslot = nr_frags &&
>  				frag_get_pending_idx(&shinfo->frags[0]) ==
>  				    copy_pending_idx(skb, copy_count(skb) - 1);
> -	int i, err;
> +	int i, err = 0;
>  
>  	for (i = 0; i < copy_count(skb); i++) {
>  		int newerr;

I'm afraid other logic (below here) is now slightly wrong as well, in
particular 

				/* If the mapping of the first frag was OK, but
				 * the header's copy failed, and they are
				 * sharing a slot, send an error
				 */
				if (i == 0 && !first_shinfo && sharedslot)
					xenvif_idx_release(queue, pending_idx,
							   XEN_NETIF_RSP_ERROR);
				else
					xenvif_idx_release(queue, pending_idx,
							   XEN_NETIF_RSP_OKAY);

which looks to be intended to deal with _only_ failure of the one shared
part of the header, whereas "err" now can indicate an error on any earlier
part as well.

Jan