netdev - [PATCH bpf 2/4] xsk: do not return EAGAIN from sendmsg when completion queue is full

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Message-Id: <1531296772-28850-3-git-send-email-magnus.karlsson@intel.com>
Date:   Wed, 11 Jul 2018 10:12:50 +0200
From:   Magnus Karlsson <magnus.karlsson@...el.com>
To:     magnus.karlsson@...el.com, bjorn.topel@...el.com, ast@...com,
        daniel@...earbox.net, netdev@...r.kernel.org,
        eric.dumazet@...il.com
Cc:     qi.z.zhang@...el.com, pavel@...tnetmon.com
Subject: [PATCH bpf 2/4] xsk: do not return EAGAIN from sendmsg when completion queue is full

This patch stops returning EAGAIN in TX copy mode when the completion
queue is full as zero-copy does not do this. Instead this situation
can be detected by comparing the head and tail pointers of the
completion queue in both modes. In any case, EAGAIN was not the
correct error code here since no amount of calling sendmsg will solve
the problem. Only consuming one or more messages on the completion
queue will fix this.

With this patch, the error reporting becomes consistent between copy
mode and zero-copy mode.

Fixes: 35fcde7f8deb ("xsk: support for Tx")
Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
---
 net/xdp/xsk.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 08d09115093e..87567232d0f8 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -233,10 +233,8 @@ static int xsk_generic_xmit(struct sock *sk, struct msghdr *m,
 			goto out;
 		}

-		if (xskq_reserve_addr(xs->umem->cq)) {
-			err = -EAGAIN;
+		if (xskq_reserve_addr(xs->umem->cq))
 			goto out;
-		}

 		len = desc.len;
 		if (unlikely(len > xs->dev->mtu)) {
-- 
2.7.4