Re: [PATCH net-next v2 2/3] rtnetlink: add IFLA_PARENT_[DEV|DEV_BUS]_NAME

On Fri, 11 Jun 2021 at 18:00, Parav Pandit [off-list ref] wrote:

quoted

From: Loic Poulain <redacted>
Sent: Friday, June 11, 2021 9:16 PM

Hi Parav,

On Fri, 11 Jun 2021 at 15:01, Parav Pandit [off-list ref] wrote:

quoted

quoted

From: Loic Poulain <redacted>
Sent: Thursday, June 10, 2021 11:15 PM

From: Johannes Berg <redacted>

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).

[...]

quoted

quoted

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..32599f3
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;

@@ -1880,6 +1890,8 @@ static const struct nla_policy

ifla_policy[IFLA_MAX+1] = {
      [IFLA_PERM_ADDRESS]     = { .type = NLA_REJECT },
      [IFLA_PROTO_DOWN_REASON] = { .type = NLA_NESTED },
      [IFLA_NEW_IFINDEX]      = NLA_POLICY_MIN(NLA_S32, 1),
+     [IFLA_PARENT_DEV_NAME]  = { .type = NLA_NUL_STRING },
+     [IFLA_PARENT_DEV_BUS_NAME] = { .type = NLA_NUL_STRING },
 };

This hunk should go in the patch that enables users to use these fields to

specify it for new link creation.

Don't get it, the previous changes I see in the tree change both if_link.h and
rtnetlink.c for new atributes (e.g. f74877a5457d). Can you elaborate on what
you expect here?

Commit f74877a5457d did in same patch because one of the objective of commit f74877a5457d is to also block PERM_ADDR using policy NLA_REJECT.
This patch-2 is not enabling user to pass these params via new_link command.
It is done in a later patch. So ifla_policy doesn’t need to have these fields in this patch.

Understood, thanks.
Loic