linux-kernel - Re: [RFC 16/19] staging: qlge: remove deadcode in qlge_build_rx

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Message-ID: <20210629133541.2n3rr7vzglcoy56x@Rk>
Date:   Tue, 29 Jun 2021 21:35:41 +0800
From:   Coiby Xu <coiby.xu@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     linux-staging@...ts.linux.dev, netdev@...r.kernel.org,
        Benjamin Poirier <benjamin.poirier@...il.com>,
        Shung-Hsi Yu <shung-hsi.yu@...e.com>,
        Manish Chopra <manishc@...vell.com>,
        "supporter:QLOGIC QLGE 10Gb ETHERNET DRIVER" 
        <GR-Linux-NIC-Dev@...vell.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 16/19] staging: qlge: remove deadcode in qlge_build_rx_skb

On Mon, Jun 28, 2021 at 09:46:45AM +0300, Dan Carpenter wrote:
>On Sun, Jun 27, 2021 at 06:53:49PM +0800, Coiby Xu wrote:
>> On Thu, Jun 24, 2021 at 03:49:26PM +0300, Dan Carpenter wrote:
>> > On Thu, Jun 24, 2021 at 07:25:00PM +0800, Coiby Xu wrote:
>> > > On Tue, Jun 22, 2021 at 10:29:39AM +0300, Dan Carpenter wrote:
>> > > > On Mon, Jun 21, 2021 at 09:48:59PM +0800, Coiby Xu wrote:
>> > > > > This part of code is for the case that "the headers and data are in
>> > > > > a single large buffer". However, qlge_process_mac_split_rx_intr is for
>> > > > > handling packets that packets underwent head splitting. In reality, with
>> > > > > jumbo frame enabled, the part of code couldn't be reached regardless of
>> > > > > the packet size when ping the NIC.
>> > > > >
>> > > >
>> > > > This commit message is a bit confusing.  We're just deleting the else
>> > > > statement.  Once I knew that then it was easy enough to review
>> > > > qlge_process_mac_rx_intr() and see that if if
>> > > > ib_mac_rsp->flags3 & IB_MAC_IOCB_RSP_DL is set then
>> > > > ib_mac_rsp->flags4 & IB_MAC_IOCB_RSP_HV must be set.
>> > >
>> > > Do you suggest moving to upper if, i.e.
>> > >
>> > >         } else if (ib_mac_rsp->flags3 & IB_MAC_IOCB_RSP_DL && ib_mac_rsp->flags4 & IB_MAC_IOCB_RSP_HS) {
>> > >
>> > > and then deleting the else statement?
>> > >
>> >
>> > I have a rule that when people whinge about commit messages they should
>> > write a better one themselves, but I have violated my own rule.  Sorry.
>> > Here is my suggestion:
>> >
>> >    If the "ib_mac_rsp->flags3 & IB_MAC_IOCB_RSP_DL" condition is true
>> >    then we know that "ib_mac_rsp->flags4 & IB_MAC_IOCB_RSP_HS" must be
>> >    true as well.  Thus, we can remove that condition and delete the
>> >    else statement which is dead code.
>> >
>> >    (Originally this code was for the case that "the headers and data are
>> >    in a single large buffer". However, qlge_process_mac_split_rx_intr
>> >    is for handling packets that packets underwent head splitting).
>>
>> Thanks for sharing your commit message! Now I see what you mean. But I'm
>> not sure if "ib_mac_rsp->flags4 & IB_MAC_IOCB_RSP_HS" is true when
>> "ib_mac_rsp->flags3 & IB_MAC_IOCB_RSP_DL" is true.
>
>Well... It is true.  qlge_process_mac_split_rx_intr() is only called
>when "->flags4 & IB_MAC_IOCB_RSP_HS" is true or when
>"->flags3 & IB_MAC_IOCB_RSP_DL" is false.

Actually qlge_process_mac_rx_intr calls qlge_process_mac_split_rx_intr when 
"ib_mac_rsp->flags4 & IB_MAC_IOCB_RSP_HV" is true or in the last else,

     /* Process an inbound completion from an rx ring. */
     static unsigned long qlge_process_mac_rx_intr(struct qlge_adapter *qdev,
     					      struct rx_ring *rx_ring,
     					      struct qlge_ib_mac_iocb_rsp *ib_mac_rsp)
     {
         ...
     	if (ib_mac_rsp->flags4 & IB_MAC_IOCB_RSP_HV) {
     		/* The data and headers are split into
     		 * separate buffers.
     		 */
     		qlge_process_mac_split_rx_intr(qdev, rx_ring, ib_mac_rsp,
     					       vlan_id);
     	} else if (ib_mac_rsp->flags3 & IB_MAC_IOCB_RSP_DS) {
             ...
     	} else {
     		/* Non-TCP/UDP large frames that span multiple buffers
     		 * can be processed corrrectly by the split frame logic.
     		 */
     		qlge_process_mac_split_rx_intr(qdev, rx_ring, ib_mac_rsp,
     					       vlan_id);
     	}

So I think we can't say that if "ib_mac_rsp->flags4 & IB_MAC_IOCB_RSP_HV" 
is true,  then "ib_mac_rsp->flags4 & IB_MAC_IOCB_RSP_HS" must be true. And 
I don't know how to reach the conclusion that the last else means 
"->flags3 & IB_MAC_IOCB_RSP_DL" is false.

>
>To me the fact that it's clearly dead code, helps me to verify that the
>patch doesn't change behavior.  Anyway, "this part of code" was a bit
>vague and it took me a while to figure out the patch deletes the else
>statement.
>
>regards,
>dan carpenter
>

-- 
Best regards,
Coiby