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SubjectRE: [PATCH] net: loopback: use NET_NAME_PREDICTABLE for name_assign_type
Date


> -----Original Message-----
> From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Sent: Wednesday, November 23, 2022 6:18 AM
> To: David S. Miller <davem@davemloft.net>; Eric Dumazet
> <edumazet@google.com>; Jakub Kicinski <kuba@kernel.org>; Paolo Abeni
> <pabeni@redhat.com>
> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>; netdev@vger.kernel.org;
> linux-kernel@vger.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 [...]
>

Heh, so the doc says loopback is an example of this but we weren't using it for that :D

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

This seems reasonable to me.

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

I don't think I would consider this a regression. Previously name_assign_type was returning an error here, now it reports something useful. And we know the name is predictable because
it is the loopback device.

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>

> 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

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