[PATCH iproute2] dcb: Do not leave ACKs in socket receive buffer

[PATCH iproute2] dcb: Do not leave ACKs in socket receive buffer

[Ido Schimmel]

Originally, the dcb utility only stopped receiving messages from a
socket when it found the attribute it was looking for. Cited commit
changed that, so that the utility will also stop when seeing an ACK
(NLMSG_ERROR message), by setting the NLM_F_ACK flag on requests.

This is problematic because it means a successful request will leave an
ACK in the socket receive buffer, causing the next request to bail
before reading its response.

Fix that by not stopping when finding the required attribute in a
response. Instead, stop on the subsequent ACK.

Fixes: 84c036972659 ("dcb: unblock mnl_socket_recvfrom if not message received")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
---
 dcb/dcb.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/dcb/dcb.c b/dcb/dcb.c
index 3ffa91d64d0d..9b996abac529 100644
--- a/dcb/dcb.c
+++ b/dcb/dcb.c
@@ -72,7 +72,7 @@ static int dcb_get_attribute_attr_ieee_cb(const struct nlattr *attr, void *data)
 
 	ga->payload = mnl_attr_get_payload(attr);
 	ga->payload_len = mnl_attr_get_payload_len(attr);
-	return MNL_CB_STOP;
+	return MNL_CB_OK;
 }
 
 static int dcb_get_attribute_attr_cb(const struct nlattr *attr, void *data)
@@ -126,7 +126,7 @@ static int dcb_set_attribute_attr_cb(const struct nlattr *attr, void *data)
 		return MNL_CB_ERROR;
 	}
 
-	return MNL_CB_STOP;
+	return MNL_CB_OK;
 }
 
 static int dcb_set_attribute_cb(const struct nlmsghdr *nlh, void *data)
-- 
2.37.3

Re: [PATCH iproute2] dcb: Do not leave ACKs in socket receive buffer

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to iproute2/iproute2.git (main)
by Stephen Hemminger <stephen@networkplumber.org>:

On Tue, 27 Dec 2022 13:03:18 +0200 you wrote:
> Originally, the dcb utility only stopped receiving messages from a
> socket when it found the attribute it was looking for. Cited commit
> changed that, so that the utility will also stop when seeing an ACK
> (NLMSG_ERROR message), by setting the NLM_F_ACK flag on requests.
> 
> This is problematic because it means a successful request will leave an
> ACK in the socket receive buffer, causing the next request to bail
> before reading its response.
> 
> [...]

Here is the summary with links:
  - [iproute2] dcb: Do not leave ACKs in socket receive buffer
    https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/commit/?id=d0e02f35af33

You are awesome, thank you!
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