netdev - Re: [net] Revert "net: core: maybe return -EEXIST in __dev_alloc

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Date:   Tue, 19 Dec 2017 23:28:21 +1100
From:   Michael Ellerman <michael@...cordia.ellerman.id.au>
To:     "Johannes Berg" <johannes@...solutions.net>
Cc:     "netdev\@vger.kernel.org" <netdev@...r.kernel.org>,
        "Jouni Malinen" <j@...fi>,
        "Rasmus Villemoes" <linux@...musvillemoes.dk>,
        "Johannes Berg" <johannes.berg@...el.com>,
        "linuxppc-dev\@lists.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [net] Revert "net: core: maybe return -EEXIST in __dev_alloc_name"

Hi Johannes,

> From: Johannes Berg <johannes.berg@...el.com>
> 
> This reverts commit d6f295e9def0; some userspace (in the case
> we noticed it's wpa_supplicant), is relying on the current
> error code to determine that a fixed name interface already
> exists.
> 
> Reported-by: Jouni Malinen <j@...fi>
> Signed-off-by: Johannes Berg <johannes.berg@...el.com>
> ---
>  net/core/dev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

This revert seems to have broken networking on one of my powerpc
machines, according to git bisect.

The symptom is DHCP fails and I don't get a link, I didn't dig any
further than that. I can if it's helpful.

I think the problem is that 87c320e51519 ("net: core: dev_get_valid_name
is now the same as dev_alloc_name_ns") only makes sense while
d6f295e9def0 remains in the tree.

ie. before the entire series, dev_get_valid_name() would return EEXIST,
and that was retained when 87c320e51519 was merged, but now that
d6f295e9def0 has been reverted dev_get_valid_name() is returning ENFILE.

I can get the network up again if I also revert 87c320e51519 ("net:
core: dev_get_valid_name is now the same as dev_alloc_name_ns"), or with
the gross patch below.

cheers

diff --git a/net/core/dev.c b/net/core/dev.c
index f47e96b62308..d0304461ad32 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1146,7 +1146,11 @@ EXPORT_SYMBOL(dev_alloc_name);
 int dev_get_valid_name(struct net *net, struct net_device *dev,
 		       const char *name)
 {
-	return dev_alloc_name_ns(net, dev, name);
+	int rc = dev_alloc_name_ns(net, dev, name);
+	if (rc == -ENFILE)
+		rc = -EEXIST;
+
+	return rc;
 }
 EXPORT_SYMBOL(dev_get_valid_name);