netdev - [RESEND net-next PATCH] net: rtnetlink: Enslave device before bringing it up

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Message-Id: <20220914150623.24152-1-phil@nwl.cc>
Date:   Wed, 14 Sep 2022 17:06:23 +0200
From:   Phil Sutter <phil@....cc>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, dsahern@...il.com
Subject: [RESEND net-next PATCH] net: rtnetlink: Enslave device before bringing it up

Unlike with bridges, one can't add an interface to a bond and set it up
at the same time:

| # ip link set dummy0 down
| # ip link set dummy0 master bond0 up
| Error: Device can not be enslaved while up.

Of all drivers with ndo_add_slave callback, bond and team decline if
IFF_UP flag is set, vrf cycles the interface (i.e., sets it down and
immediately up again) and the others just don't care.

Support the common notion of setting the interface up after enslaving it
by sorting the operations accordingly.

Signed-off-by: Phil Sutter <phil@....cc>
---
Resubmitting this after review, concerns uttered in original discussion
three years ago do not apply: Any flag changes happening during
do_set_master() call are preserved, unless user space intended to change
them. I verified that a team device in promisc mode still correctly
propagates the flag to a new slave after applying this patch.
---
 net/core/rtnetlink.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index ac45328607f77..2e15f744544e5 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -2776,13 +2776,6 @@ static int do_setlink(const struct sk_buff *skb,
 		call_netdevice_notifiers(NETDEV_CHANGEADDR, dev);
 	}
 
-	if (ifm->ifi_flags || ifm->ifi_change) {
-		err = dev_change_flags(dev, rtnl_dev_combine_flags(dev, ifm),
-				       extack);
-		if (err < 0)
-			goto errout;
-	}
-
 	if (tb[IFLA_MASTER]) {
 		err = do_set_master(dev, nla_get_u32(tb[IFLA_MASTER]), extack);
 		if (err)
@@ -2790,6 +2783,13 @@ static int do_setlink(const struct sk_buff *skb,
 		status |= DO_SETLINK_MODIFIED;
 	}
 
+	if (ifm->ifi_flags || ifm->ifi_change) {
+		err = dev_change_flags(dev, rtnl_dev_combine_flags(dev, ifm),
+				       extack);
+		if (err < 0)
+			goto errout;
+	}
+
 	if (tb[IFLA_CARRIER]) {
 		err = dev_change_carrier(dev, nla_get_u8(tb[IFLA_CARRIER]));
 		if (err)
-- 
2.34.1