Re: [Xen-devel] [PATCH 4/6] xen/netback: Always pull through PKT_PROT_LEN bytes into the linear part of an skb.

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

Could you point out what problem this addresses?

Thanks, Jan

>>> Ian Campbell <ian.campbell@xxxxxxxxxx> 23.02.10 17:47 >>>
Previously PKT_PROT_LEN would only have an effect on the first fragment.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 drivers/xen/netback/netback.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/drivers/xen/netback/netback.c b/drivers/xen/netback/netback.c
index 7e1dfd1..e668704 100644
--- a/drivers/xen/netback/netback.c
+++ b/drivers/xen/netback/netback.c
@@ -1346,6 +1346,16 @@ static void net_tx_submit(void)
 
                netbk_fill_frags(skb);
 
+               /*
+                * If the initial fragment was < PKT_PROT_LEN then
+                * pull through some bytes from the other fragments to
+                * increase the linear region to PKT_PROT_LEN bytes.
+                */
+               if (skb_headlen(skb) < PKT_PROT_LEN && skb_is_nonlinear(skb)) {
+                       int target = min_t(int, skb->len, PKT_PROT_LEN);
+                       __pskb_pull_tail(skb, target - skb_headlen(skb));
+               }
+
                skb->dev      = netif->dev;
                skb->protocol = eth_type_trans(skb, skb->dev);
 
-- 
1.5.6.5


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