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

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Message-ID: <20210628064645.GK2040@kadam>
Date:   Mon, 28 Jun 2021 09:46:45 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Coiby Xu <coiby.xu@...il.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 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.

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