diff mbox

[iproute,v3,1/2] libnetlink: add a variant of rtnl_send_check that consumes ACKs

Message ID 1450773094-7978-2-git-send-email-lorenzo@google.com
State Rejected, archived
Delegated to: stephen hemminger
Headers show

Commit Message

Lorenzo Colitti Dec. 22, 2015, 8:31 a.m. UTC 
The new variant is identical to rtnl_send_check, except it also
consumes the kernel response instead of using MSG_PEEK. This is
useful for callers that send simple commands that never cause a
response but only ACKs, and that expect to receive and deal
with errors without printing them to stderr like rtnl_talk does.

Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
---
 include/libnetlink.h |  2 ++
 lib/libnetlink.c     | 16 +++++++++++++---
 2 files changed, 15 insertions(+), 3 deletions(-)

Comments

Stephen Hemminger Dec. 23, 2015, 9:17 p.m. UTC | #1 
On Tue, 22 Dec 2015 17:31:33 +0900
Lorenzo Colitti <lorenzo@google.com> wrote:

> The new variant is identical to rtnl_send_check, except it also
> consumes the kernel response instead of using MSG_PEEK. This is
> useful for callers that send simple commands that never cause a
> response but only ACKs, and that expect to receive and deal
> with errors without printing them to stderr like rtnl_talk does.
> 
> Signed-off-by: Lorenzo Colitti <lorenzo@google.com>

Originally, iproute2 used netlink so that every request had an ACK and
this is the API in rtnl_talk. Then as an optimization it was observed
that ACK from kernel is not necessary (all error reports are handled in
send), but that for some asynchronous errors a check was necessary.

Therefore, I wonder why you need this, either:
 * don't ask kernel for ACK's (like most other ip commands),
 * or use rtnl_talk() and expect ACK.



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diff mbox

Patch

diff --git a/include/libnetlink.h b/include/libnetlink.h
index 431189e..a88cb4d 100644
--- a/include/libnetlink.h
+++ b/include/libnetlink.h
@@ -75,6 +75,8 @@  int rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n,
 	__attribute__((warn_unused_result));
 int rtnl_send(struct rtnl_handle *rth, const void *buf, int)
 	__attribute__((warn_unused_result));
+int rtnl_send_check_ack(struct rtnl_handle *rth, const void *buf, int, int)
+	__attribute__((warn_unused_result));
 int rtnl_send_check(struct rtnl_handle *rth, const void *buf, int)
 	__attribute__((warn_unused_result));
 
diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index 1658214..43cc73b 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -134,18 +134,21 @@  int rtnl_send(struct rtnl_handle *rth, const void *buf, int len)
 	return send(rth->fd, buf, len, 0);
 }
 
-int rtnl_send_check(struct rtnl_handle *rth, const void *buf, int len)
+int rtnl_send_check_ack(struct rtnl_handle *rth, const void *buf, int len,
+		int ack)
 {
 	struct nlmsghdr *h;
-	int status;
+	int status, flags;
 	char resp[1024];
 
 	status = send(rth->fd, buf, len, 0);
 	if (status < 0)
 		return status;
 
+	flags = ack ? 0 : MSG_DONTWAIT|MSG_PEEK;
+
 	/* Check for immediate errors */
-	status = recv(rth->fd, resp, sizeof(resp), MSG_DONTWAIT|MSG_PEEK);
+	status = recv(rth->fd, resp, sizeof(resp), flags);
 	if (status < 0) {
 		if (errno == EAGAIN)
 			return 0;
@@ -160,6 +163,8 @@  int rtnl_send_check(struct rtnl_handle *rth, const void *buf, int len)
 				fprintf(stderr, "ERROR truncated\n");
 			else 
 				errno = -err->error;
+			if (ack && errno == 0)
+				return 0;
 			return -1;
 		}
 	}
@@ -167,6 +172,11 @@  int rtnl_send_check(struct rtnl_handle *rth, const void *buf, int len)
 	return 0;
 }
 
+int rtnl_send_check(struct rtnl_handle *rth, const void *buf, int len)
+{
+	return rtnl_send_check_ack(rth, buf, len, 0);
+}
+
 int rtnl_dump_request(struct rtnl_handle *rth, int type, void *req, int len)
 {
 	struct nlmsghdr nlh;