netdev - Re: [PATCH V4 2/8] netdevice.h: Add a new zerocopy device flag

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Date:	Thu, 05 May 2011 14:02:17 -0700
From:	Shirley Ma <mashirle@...ibm.com>
To:	Sridhar Samudrala <sri@...ibm.com>
Cc:	David Miller <davem@...emloft.net>, mst@...hat.com,
	Eric Dumazet <eric.dumazet@...il.com>,
	Avi Kivity <avi@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	netdev@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 2/8] netdevice.h: Add a new zerocopy device flag

On Wed, 2011-05-04 at 16:13 -0700, Sridhar Samudrala wrote:
> On Wed, 2011-05-04 at 00:55 -0700, Shirley Ma wrote: 
> > Signed-off-by: Shirley Ma <xma@...ibm.com>
> > ---
> > 
> >  include/linux/netdevice.h |   10 ++++++++++
> >  1 files changed, 10 insertions(+), 0 deletions(-)
> > 
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index 0249fe7..0808f1e 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -1067,6 +1067,16 @@ struct net_device {
> >  #define NETIF_F_RXHASH		(1 << 28) /* Receive hashing offload */
> >  #define NETIF_F_RXCSUM		(1 << 29) /* Receive checksumming offload */
> > 
> > +/*
> > + * Bit 31 is for device to map userspace buffers -- zerocopy
> > + * Device can set this flag when it supports HIGHDMA.
> > + * Device can't recycle this kind of skb buffers.
> > + * There are 256 bytes copied, the rest of buffers are mapped.
> > + * The userspace callback should only be called when last reference to this skb
> > + * is gone.
> > + */
> > +#define NETIF_F_ZEROCOPY	(1 << 31)
> > +
> Should we make this TX_ZEROCOPY as we may need a seperate flag for
> RX_ZEROCOPY in future?
> 
> Same with socket flag.

We might be able to use the same flag for both TX and RX. If RX
zero-copy requires only HIGHDMA feature only. If not, then we might need
different feature bit. Same for sock flag.

> Thanks
> Sridhar
> 
> 

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