sock: enable MSG_ZEROCOPY
Prepare the datapath for refcounted ubuf_info. Clone ubuf_info with
skb_zerocopy_clone() wherever needed due to skb split, merge, resize
or clone.
Split skb_orphan_frags into two variants. The split, merge, .. paths
support reference counted zerocopy buffers, so do not do a deep copy.
Add skb_orphan_frags_rx for paths that may loop packets to receive
sockets. That is not allowed, as it may cause unbounded latency.
Deep copy all zerocopy copy buffers, ref-counted or not, in this path.
The exact locations to modify were chosen by exhaustively searching
through all code that might modify skb_frag references and/or the
the SKBTX_DEV_ZEROCOPY tx_flags bit.
The changes err on the safe side, in two ways.
(1) legacy ubuf_info paths virtio and tap are not modified. They keep
a 1:1 ubuf_info to sk_buff relationship. Calls to skb_orphan_frags
still call skb_copy_ubufs and thus copy frags in this case.
(2) not all copies deep in the stack are addressed yet. skb_shift,
skb_split and skb_try_coalesce can be refined to avoid copying.
These are not in the hot path and this patch is hairy enough as
is, so that is left for future refinement.
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 59cff7a..e538793 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2512,7 +2512,17 @@ static inline void skb_orphan(struct sk_buff *skb)
*/
static inline int skb_orphan_frags(struct sk_buff *skb, gfp_t gfp_mask)
{
- if (likely(!(skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY)))
+ if (likely(!skb_zcopy(skb)))
+ return 0;
+ if (skb_uarg(skb)->callback == sock_zerocopy_callback)
+ return 0;
+ return skb_copy_ubufs(skb, gfp_mask);
+}
+
+/* Frags must be orphaned, even if refcounted, if skb might loop to rx path */
+static inline int skb_orphan_frags_rx(struct sk_buff *skb, gfp_t gfp_mask)
+{
+ if (likely(!skb_zcopy(skb)))
return 0;
return skb_copy_ubufs(skb, gfp_mask);
}
@@ -2944,6 +2954,8 @@ static inline int skb_add_data(struct sk_buff *skb,
static inline bool skb_can_coalesce(struct sk_buff *skb, int i,
const struct page *page, int off)
{
+ if (skb_zcopy(skb))
+ return false;
if (i) {
const struct skb_frag_struct *frag = &skb_shinfo(skb)->frags[i - 1];