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

[Jan Beulich <jbeulich@xxxxxxxx>]

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@xxxxxxxx>
>>
>> --- 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