linux-kernel - Re: [PATCH] net: core: datagram: tidy up copy functions a bit

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Date:   Sun, 13 Oct 2019 15:41:48 -0700
From:   Vito Caputo <vcaputo@...garu.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: core: datagram: tidy up copy functions a bit

On Sun, Oct 13, 2019 at 01:17:18PM -0700, Eric Dumazet wrote:
> 
> 
> On 10/13/19 1:01 PM, Vito Caputo wrote:
> > On Sun, Oct 13, 2019 at 12:30:41PM -0700, Eric Dumazet wrote:
> >>
> >>
> >> On 10/12/19 4:55 AM, Vito Caputo wrote:
> >>> Eliminate some verbosity by using min() macro and consolidating some
> >>> things, also fix inconsistent zero tests (! vs. == 0).
> >>>
> >>> Signed-off-by: Vito Caputo <vcaputo@...garu.com>
> >>> ---
> >>>  net/core/datagram.c | 44 ++++++++++++++------------------------------
> >>>  1 file changed, 14 insertions(+), 30 deletions(-)
> >>>
> >>> diff --git a/net/core/datagram.c b/net/core/datagram.c
> >>> index 4cc8dc5db2b7..08d403f93952 100644
> >>> --- a/net/core/datagram.c
> >>> +++ b/net/core/datagram.c
> >>> @@ -413,13 +413,11 @@ static int __skb_datagram_iter(const struct sk_buff *skb, int offset,
> >>>  					    struct iov_iter *), void *data)
> >>>  {
> >>>  	int start = skb_headlen(skb);
> >>> -	int i, copy = start - offset, start_off = offset, n;
> >>> +	int i, copy, start_off = offset, n;
> >>>  	struct sk_buff *frag_iter;
> >>>  
> >>>  	/* Copy header. */
> >>> -	if (copy > 0) {
> >>> -		if (copy > len)
> >>> -			copy = len;
> >>> +	if ((copy = min(start - offset, len)) > 0) {
> >>
> >> No, we prefer not having this kind of construct anymore.
> >>
> >> This refactoring looks unnecessary code churn, making our future backports not
> >> clean cherry-picks.
> >>
> >> Simply making sure this patch does not bring a regression is very time consuming.
> > 
> > Should I not bother submitting patches for such cleanups?
> > 
> > I submitted another, more trivial patch, is it also considered unnecessary churn:
> > 
> > ---
> > 
> > Author: Vito Caputo <vcaputo@...garu.com>
> > Date:   Sat Oct 12 17:10:41 2019 -0700
> > 
> >     net: core: skbuff: skb_checksum_setup() drop err
> >     
> >     Return directly from all switch cases, no point in storing in err.
> >     
> >     Signed-off-by: Vito Caputo <vcaputo@...garu.com>
> > 
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index f5f904f46893..c59b68a413b5 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -4888,23 +4888,14 @@ static int skb_checksum_setup_ipv6(struct sk_buff *skb, bool recalculate)
> >   */
> >  int skb_checksum_setup(struct sk_buff *skb, bool recalculate)
> >  {
> > -       int err;
> > -
> >         switch (skb->protocol) {
> >         case htons(ETH_P_IP):
> > -               err = skb_checksum_setup_ipv4(skb, recalculate);
> > -               break;
> > -
> > +               return skb_checksum_setup_ipv4(skb, recalculate);
> >         case htons(ETH_P_IPV6):
> > -               err = skb_checksum_setup_ipv6(skb, recalculate);
> > -               break;
> > -
> > +               return skb_checksum_setup_ipv6(skb, recalculate);
> >         default:
> > -               err = -EPROTO;
> > -               break;
> > +               return -EPROTO;
> >         }
> > -
> > -       return err;
> >  }
> >  EXPORT_SYMBOL(skb_checksum_setup);
> > 
> > ---
> > 
> > Asking to calibrate my thresholds to yours, since I was planning to volunteer
> > some time each evening to reading kernel code and submitting any obvious
> > cleanups.
> > 
> 
> This is not a cleanup.
> 
> You prefer seeing the code written the way you did, but that is really a matter of taste.
> 

I respectfully disagree with your assertion.  When the diff --stat shows
more lines removed than added without harming readability, preferably
improving readability, it's both a cleanup and not a debatable matter of
taste.  Having the quantifiable metric of fewer lines of code matters.

> Think about backports of real bug fixes to stable kernels.
> 

That's fair, but when the change is an isolated mechanical one in a
single small function, as the one quoted above - is that really of any
significant burden on backports?

> Having these re-writes of code make things less easy for us really.
> So in general we tend to leave the existing code style.
> 
> I already replied to the other patch submission, please read
> 
> https://marc.info/?l=linux-netdev&m=157099669227635&w=2
> 

I read it, thank you for your responses.

Do you have any guidance to offer someone wanting to contribute with 1-2
hours available per day?  I don't want to cause a nuisance, but would
like to help where I can.  My flawed assumption was that small, isolated
hygienic contributions without functionally changing anything would be
appropriate.

Thanks,
Vito Caputo