netdev - [PATCH net-next v3 2/4] rtnetlink: add IFLA_PARENT_[DEV|DEV_BUS]

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Message-Id: <1623486057-13075-3-git-send-email-loic.poulain@linaro.org>
Date:   Sat, 12 Jun 2021 10:20:55 +0200
From:   Loic Poulain <loic.poulain@...aro.org>
To:     kuba@...nel.org, davem@...emloft.net
Cc:     netdev@...r.kernel.org, m.chetan.kumar@...el.com,
        johannes.berg@...el.com, leon@...nel.org, ryazanov.s.a@...il.com,
        parav@...dia.com, Loic Poulain <loic.poulain@...aro.org>
Subject: [PATCH net-next v3 2/4] rtnetlink: add IFLA_PARENT_[DEV|DEV_BUS]_NAME

From: Johannes Berg <johannes.berg@...el.com>

In some cases, for example in the upcoming WWAN framework changes,
there's no natural "parent netdev", so sometimes dummy netdevs are
created or similar. IFLA_PARENT_DEV_NAME is a new attribute intended to
contain a device (sysfs, struct device) name that can be used instead
when creating a new netdev, if the rtnetlink family implements it.

As suggested by Parav Pandit, we also introduce IFLA_PARENT_DEV_BUS_NAME
attribute in order to uniquely identify a device on the system (with
bus/name pair).

ip-link(8) support for the generic parent device attributes will help
us avoid code duplication, so no other link type will require a custom
code to handle the parent name attribute. E.g. the WWAN interface
creation command will looks like this:

$ ip link add wwan0-1 parent-dev wwan0 type wwan channel-id 1

So, some future subsystem (or driver) FOO will have an interface
creation command that looks like this:

$ ip link add foo1-3 parent-dev foo1 type foo bar-id 3 baz-type Y

Below is an example of dumping link info of a random device with these
new attributes:

$ ip --details link show wlp0s20f3
  4: wlp0s20f3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue
     state UP mode DORMANT group default qlen 1000
     ...
     parent_bus pci parent_dev 0000:00:14.3

Co-developed-by: Sergey Ryazanov <ryazanov.s.a@...il.com>
Signed-off-by: Sergey Ryazanov <ryazanov.s.a@...il.com>
Co-developed-by: Loic Poulain <loic.poulain@...aro.org>
Signed-off-by: Loic Poulain <loic.poulain@...aro.org>
Suggested-by: Sergey Ryazanov <ryazanov.s.a@...il.com>
Signed-off-by: Johannes Berg <johannes.berg@...el.com>
---
 include/uapi/linux/if_link.h |  7 +++++++
 net/core/rtnetlink.c         | 10 ++++++++++
 2 files changed, 17 insertions(+)

diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index a5a7f0e..4882e81 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -341,6 +341,13 @@ enum {
 	IFLA_ALT_IFNAME, /* Alternative ifname */
 	IFLA_PERM_ADDRESS,
 	IFLA_PROTO_DOWN_REASON,
+
+	/* device (sysfs) name as parent, used instead
+	 * of IFLA_LINK where there's no parent netdev
+	 */
+	IFLA_PARENT_DEV_NAME,
+	IFLA_PARENT_DEV_BUS_NAME,
+
 	__IFLA_MAX
 };
 
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 92c3e43..170e97f 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1821,6 +1821,16 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
 	if (rtnl_fill_prop_list(skb, dev))
 		goto nla_put_failure;
 
+	if (dev->dev.parent &&
+	    nla_put_string(skb, IFLA_PARENT_DEV_NAME,
+			   dev_name(dev->dev.parent)))
+		goto nla_put_failure;
+
+	if (dev->dev.parent && dev->dev.parent->bus &&
+	    nla_put_string(skb, IFLA_PARENT_DEV_BUS_NAME,
+			   dev->dev.parent->bus->name))
+		goto nla_put_failure;
+
 	nlmsg_end(skb, nlh);
 	return 0;
 
-- 
2.7.4