[nft PATCH 0/2] Fix and simplify mnl_batch_talk()

[nft PATCH 0/2] Fix and simplify mnl_batch_talk()

[Phil Sutter]

As requested, here's the mnl_batch_talk() fix extracted from previous
series. To make things more clear, I've split this into a very minimal
FD_SET/select reordering fix and a follow-up simplifying the code a bit.

Feel free to fold into your own series and/or dismiss second patch at
your own convenience. :)

Phil Sutter (2):
  mnl: Initialize fd_set before select(), not after
  mnl: Simplify mnl_batch_talk()

 src/mnl.c | 26 +++++++++++---------------
 1 file changed, 11 insertions(+), 15 deletions(-)

-- 
2.21.0

[nft PATCH 1/2] mnl: Initialize fd_set before select(), not after

[Phil Sutter]

Calling FD_SET() in between return of select() and call to FD_ISSET()
effectively renders the whole thing useless: FD_ISSET() will always
return true no matter what select() actually did.

Fixes: a72315d2bad47 ("src: add rule batching support")
Signed-off-by: Phil Sutter <phil@nwl.cc>
---
 src/mnl.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/mnl.c b/src/mnl.c
index f6363560721c1..492d7517d40e2 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -300,12 +300,12 @@ int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list)
 			err = -1;
 		}
 
+		FD_ZERO(&readfds);
+		FD_SET(fd, &readfds);
+
 		ret = select(fd+1, &readfds, NULL, NULL, &tv);
 		if (ret == -1)
 			return -1;
-
-		FD_ZERO(&readfds);
-		FD_SET(fd, &readfds);
 	}
 	return err;
 }
-- 
2.21.0

[nft PATCH 2/2] mnl: Simplify mnl_batch_talk()

[Phil Sutter]

By mimicking mnl_nft_event_listener() code, mnl_batch_talk() may be
simplified quite a bit:

* Turn the conditional loop into an unconditional one.
* Call select() at loop start, which merges the two call sites.
* Check readfds content after select() returned instead of in loop
  condition - if fd is not set, break to return error state stored in
  'err' variable.
* Old code checked that select() return code is > 0, but that was
  redundant: if FD_ISSET() returns true, select return code was 1.
* Move 'nlh' helper variable definition into error handling block, it is
  not used outside of it.

Signed-off-by: Phil Sutter <phil@nwl.cc>
---
 src/mnl.c | 26 +++++++++++---------------
 1 file changed, 11 insertions(+), 15 deletions(-)

diff --git a/src/mnl.c b/src/mnl.c
index 492d7517d40e2..724decad2e44d 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -278,16 +278,17 @@ int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list)
 	if (ret == -1)
 		return -1;
 
-	FD_ZERO(&readfds);
-	FD_SET(fd, &readfds);
-
 	/* receive and digest all the acknowledgments from the kernel. */
-	ret = select(fd+1, &readfds, NULL, NULL, &tv);
-	if (ret == -1)
-		return -1;
+	while (true) {
+		FD_ZERO(&readfds);
+		FD_SET(fd, &readfds);
+
+		ret = select(fd+1, &readfds, NULL, NULL, &tv);
+		if (ret == -1)
+			return -1;
 
-	while (ret > 0 && FD_ISSET(fd, &readfds)) {
-		struct nlmsghdr *nlh = (struct nlmsghdr *)rcv_buf;
+		if (!FD_ISSET(fd, &readfds))
+			break;
 
 		ret = mnl_socket_recvfrom(nl, rcv_buf, sizeof(rcv_buf));
 		if (ret == -1)
@@ -296,16 +297,11 @@ int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list)
 		ret = mnl_cb_run(rcv_buf, ret, 0, portid, &netlink_echo_callback, ctx);
 		/* Continue on error, make sure we get all acknowledgments */
 		if (ret == -1) {
+			struct nlmsghdr *nlh = (struct nlmsghdr *)rcv_buf;
+
 			mnl_err_list_node_add(err_list, errno, nlh->nlmsg_seq);
 			err = -1;
 		}
-
-		FD_ZERO(&readfds);
-		FD_SET(fd, &readfds);
-
-		ret = select(fd+1, &readfds, NULL, NULL, &tv);
-		if (ret == -1)
-			return -1;
 	}
 	return err;
 }
-- 
2.21.0

Re: [nft PATCH 0/2] Fix and simplify mnl_batch_talk()

[Pablo Neira Ayuso]

On Fri, May 31, 2019 at 04:17:41PM +0200, Phil Sutter wrote:
> As requested, here's the mnl_batch_talk() fix extracted from previous
> series. To make things more clear, I've split this into a very minimal
> FD_SET/select reordering fix and a follow-up simplifying the code a bit.

Series applied, thanks Phil.