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

Coiby Xu
2021-06-29T13:37:14Z

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