Re: [RFC 16/19] staging: qlge: remove deadcode in qlge_build_rx_skb

[Coiby Xu]

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