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: 

quoted

Signed-off-by: Shirley Ma <redacted>
---

 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