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Date:   Fri,  4 Sep 2020 15:53:26 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     ast@...nel.org, daniel@...earbox.net, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        magnus.karlsson@...el.com, davem@...emloft.net, kuba@...nel.org,
        hawk@...nel.org, john.fastabend@...il.com,
        intel-wired-lan@...ts.osuosl.org
Subject: [PATCH bpf-next 1/6] xsk: improve xdp_do_redirect() error codes

From: Björn Töpel <bjorn.topel@...el.com>

The error codes returned by xdp_do_redirect() when redirecting a frame
to an AF_XDP socket has not been very useful. A driver could not
distinguish between different errors. Prior this change the following
codes where used:

Socket not bound or incorrect queue/netdev: EINVAL
XDP frame/AF_XDP buffer size mismatch: ENOSPC
Could not allocate buffer (copy mode): ENOSPC
AF_XDP Rx buffer full: ENOSPC

After this change:

Socket not bound or incorrect queue/netdev: EINVAL
XDP frame/AF_XDP buffer size mismatch: ENOSPC
Could not allocate buffer (copy mode): ENOMEM
AF_XDP Rx buffer full: ENOBUFS

An AF_XDP zero-copy driver can now potentially determine if the
failure was due to a full Rx buffer, and if so stop processing more
frames, yielding to the userland AF_XDP application.

Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
---
 net/xdp/xsk.c       | 2 +-
 net/xdp/xsk_queue.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 3895697f8540..db38560c4af7 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -197,7 +197,7 @@ static int __xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len,
 	xsk_xdp = xsk_buff_alloc(xs->pool);
 	if (!xsk_xdp) {
 		xs->rx_dropped++;
-		return -ENOSPC;
+		return -ENOMEM;
 	}
 
 	xsk_copy_xdp(xsk_xdp, xdp, len);
diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
index 2d883f631c85..b76966cf122e 100644
--- a/net/xdp/xsk_queue.h
+++ b/net/xdp/xsk_queue.h
@@ -305,7 +305,7 @@ static inline int xskq_prod_reserve_desc(struct xsk_queue *q,
 	u32 idx;
 
 	if (xskq_prod_is_full(q))
-		return -ENOSPC;
+		return -ENOBUFS;
 
 	/* A, matches D */
 	idx = q->cached_prod++ & q->ring_mask;
-- 
2.25.1

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