netdev - Re: [PATCH 05/12 v2 RFC] skbuff: replace sock_zerocopy_put() with skb_zcopy

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Message-ID: <20201222171940.ijpuhkuxhvk33czg@bsd-mbp.dhcp.thefacebook.com>
Date:   Tue, 22 Dec 2020 09:19:40 -0800
From:   Jonathan Lemon <jonathan.lemon@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH 05/12 v2 RFC] skbuff: replace sock_zerocopy_put() with
 skb_zcopy_put()

On Tue, Dec 22, 2020 at 09:42:40AM -0500, Willem de Bruijn wrote:
> On Mon, Dec 21, 2020 at 7:09 PM Jonathan Lemon <jonathan.lemon@...il.com> wrote:
> >
> > From: Jonathan Lemon <bsd@...com>
> >
> > Replace sock_zerocopy_put with the generic skb_zcopy_put()
> > function.  Pass 'true' as the success argument, as this
> > is identical to no change.
> >
> > Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com>
> 
> uarg->zerocopy may be false if sock_zerocopy_put_abort is called from
> tcp_sendmsg_locked

Yes, it may well be false.  The original logic goes:

   sock_zerocopy_put_abort()
   sock_zerocopy_put()
   sock_zerocopy_callback(..., success = uarg->zerocopy)
     if (success)

The new logic is now:

   sock_zerocopy_put_abort()
   sock_zerocopy_callback(..., success = true)
     uarg->zerocopy = uarg->zerocopy & success
     if (uarg->zerocopy)

The success value ls latched into uarg->zerocopy, and any failure
is persistent.  Hence my comment about passing 'true' not changing
the logic.
-- 
Jonathan