linux-kernel - Re: [PATCH -next] packet: remove unused variable 'status' in __packet_lookup_frame_in

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Date:   Mon, 10 Jun 2019 22:02:32 +0800
From:   maowenan <maowenan@...wei.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
CC:     David Miller <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH -next] packet: remove unused variable 'status' in
 __packet_lookup_frame_in_block



On 2019/6/10 21:05, Willem de Bruijn wrote:
> On Mon, Jun 10, 2019 at 8:17 AM Mao Wenan <maowenan@...wei.com> wrote:
>>
>> The variable 'status' in  __packet_lookup_frame_in_block() is never used since
>> introduction in commit f6fb8f100b80 ("af-packet: TPACKET_V3 flexible buffer
>> implementation."), we can remove it.
>> And when __packet_lookup_frame_in_block() calls prb_retire_current_block(),
>> it can pass macro TP_STATUS_KERNEL instead of 0.
>>
>> Signed-off-by: Mao Wenan <maowenan@...wei.com>
>> ---
>>  net/packet/af_packet.c | 5 ++---
>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
>> index a29d66d..fb1a79c 100644
>> --- a/net/packet/af_packet.c
>> +++ b/net/packet/af_packet.c
>> @@ -1003,7 +1003,6 @@ static void prb_fill_curr_block(char *curr,
>>  /* Assumes caller has the sk->rx_queue.lock */
>>  static void *__packet_lookup_frame_in_block(struct packet_sock *po,
>>                                             struct sk_buff *skb,
>> -                                               int status,
>>                                             unsigned int len
>>                                             )
>>  {
>> @@ -1046,7 +1045,7 @@ static void *__packet_lookup_frame_in_block(struct packet_sock *po,
>>         }
>>
>>         /* Ok, close the current block */
>> -       prb_retire_current_block(pkc, po, 0);
>> +       prb_retire_current_block(pkc, po, TP_STATUS_KERNEL);
> 
> I don't think that 0 is intended to mean TP_STATUS_KERNEL here.
> 
> prb_retire_current_block calls prb_close_block which sets status to
> 
>   TP_STATUS_USER | stat
> 
> where stat is 0 or TP_STATUS_BLK_TMO.


#define TP_STATUS_KERNEL		      0
#define TP_STATUS_BLK_TMO		(1 << 5)

Actually, packet_current_rx_frame calls __packet_lookup_frame_in_block with status=TP_STATUS_KERNEL
in original code.

__packet_lookup_frame_in_block in this function, first is to check whether the currently active block
has enough space for the packet, which means status of block should be TP_STATUS_KERNEL, then it calls
prb_retire_current_block to retire this block.

Since there needs some discussion about means of status, I can send v2 only removing the parameter status of
__packet_lookup_frame_in_block?

> 
>