linux-kernel - [PATCH] net: loopback: use NET_NAME_PREDICTABLE for name_assign

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Message-Id: <20221123141829.1825170-1-linux@rasmusvillemoes.dk>
Date:   Wed, 23 Nov 2022 15:18:28 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] net: loopback: use NET_NAME_PREDICTABLE for name_assign_type

When the name_assign_type attribute was introduced (commit
685343fc3ba6, "net: add name_assign_type netdev attribute"), the
loopback device was explicitly mentioned as one which would make use
of NET_NAME_PREDICTABLE:

    The name_assign_type attribute gives hints where the interface name of a
    given net-device comes from. These values are currently defined:
...
      NET_NAME_PREDICTABLE:
        The ifname has been assigned by the kernel in a predictable way
        that is guaranteed to avoid reuse and always be the same for a
        given device. Examples include statically created devices like
        the loopback device [...]

Switch to that so that reading /sys/class/net/lo/name_assign_type
produces something sensible instead of returning -EINVAL.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---

This is mostly cosmetic, but ideally I'd like to get to a situation
where I don't need to do

  assign_type=$(cat /sys/class/net/$dev/name_assign_type 2> /dev/null || echo 0)

or otherwise special-case [ $dev = "lo" ].

As always, there's a small chance that this could cause a regression,
but it seems extremely unlikely that anybody relies on
/sys/class/net/lo/name_assign_type being unreadable and thus
effectively is known to be NET_NAME_UNKNOWN.

 drivers/net/loopback.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
index 14e8d04cb434..2e9742952c4e 100644
--- a/drivers/net/loopback.c
+++ b/drivers/net/loopback.c
@@ -211,7 +211,7 @@ static __net_init int loopback_net_init(struct net *net)
 	int err;
 
 	err = -ENOMEM;
-	dev = alloc_netdev(0, "lo", NET_NAME_UNKNOWN, loopback_setup);
+	dev = alloc_netdev(0, "lo", NET_NAME_PREDICTABLE, loopback_setup);
 	if (!dev)
 		goto out;
 
-- 
2.37.2