netdev - Re: [PATCH] xen-netback: correct success/error reporting for the SKB-with-fraglist case

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Date:   Thu, 25 Feb 2021 08:33:41 +0100
From:   Jan Beulich <jbeulich@...e.com>
To:     paul@....org
Cc:     "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Wei Liu <wl@....org>
Subject: Re: [PATCH] xen-netback: correct success/error reporting for the
 SKB-with-fraglist case

On 24.02.2021 17:39, Paul Durrant wrote:
> On 23/02/2021 16:29, Jan Beulich wrote:
>> When re-entering the main loop of xenvif_tx_check_gop() a 2nd time, the
>> special considerations for the head of the SKB no longer apply. Don't
>> mistakenly report ERROR to the frontend for the first entry in the list,
>> even if - from all I can tell - this shouldn't matter much as the overall
>> transmit will need to be considered failed anyway.
>>
>> Signed-off-by: Jan Beulich <jbeulich@...e.com>
>>
>> --- a/drivers/net/xen-netback/netback.c
>> +++ b/drivers/net/xen-netback/netback.c
>> @@ -499,7 +499,7 @@ check_frags:
>>   				 * the header's copy failed, and they are
>>   				 * sharing a slot, send an error
>>   				 */
>> -				if (i == 0 && sharedslot)
>> +				if (i == 0 && !first_shinfo && sharedslot)
>>   					xenvif_idx_release(queue, pending_idx,
>>   							   XEN_NETIF_RSP_ERROR);
>>   				else
>>
> 
> I think this will DTRT, but to my mind it would make more sense to clear 
> 'sharedslot' before the 'goto check_frags' at the bottom of the function.

That was my initial idea as well, but
- I think it is for a reason that the variable is "const".
- There is another use of it which would then instead need further
  amending (and which I believe is at least part of the reason for
  the variable to be "const").

Jan