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

[David Miller <davem@davemloft.net>]

From: Michael Ellerman <mpe@ellerman.id.au>
Date: Fri, 22 Dec 2017 15:22:22 +1100

>> On Tue, Dec 19 2017, Michael Ellerman <michael@concordia.ellerman.id.au> wrote:
>>> 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.
>>
>> I'm sorry about all of this, I really didn't think there would be such
>> consequences of changing an errno return. Indeed, d6f29 was preparation
>> for unifying the two functions that do the exact same thing (and how we
>> ever got into that situation is somewhat unclear), except for
>> their behaviour in the case the requested name already exists. So one of
>> the two interfaces had to change its return value, and as I wrote, I
>> thought EEXIST was the saner choice when an explicit name (no %d) had
>> been requested.
> 
> No worries.
> 
>>> 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.
>>
>> I don't think changing -ENFILE to -EEXIST would be right either, since
>> dev_get_valid_name() used to be able to return both (-EEXIST in the case
>> where there's no %d, -ENFILE in the case where we end up calling
>> dev_alloc_name_ns()). If anything, we could do the check for the old
>> -EEXIST condition first, and then call dev_alloc_name_ns(). But I'm also
>> fine with reverting.
> 
> Yeah I think a revert would be best, given it's nearly rc5.
> 
> My userspace is not exotic AFAIK, just debian something, so presumably
> this will affect other people too.

I've just queued up the following revert, thanks!

====================
>From 5047543928139184f060c8f3bccb788b3df4c1ea Mon Sep 17 00:00:00 2001
From: "David S. Miller" <davem@davemloft.net>
Date: Tue, 2 Jan 2018 11:45:07 -0500
Subject: [PATCH] Revert "net: core: dev_get_valid_name is now the same as
 dev_alloc_name_ns"

This reverts commit 87c320e51519a83c496ab7bfb4e96c8f9c001e89.

Changing the error return code in some situations turns out to
be harmful in practice.  In particular Michael Ellerman reports
that DHCP fails on his powerpc machines, and this revert gets
things working again.

Johannes Berg agrees that this revert is the best course of
action for now.

Fixes: 029b6d140550 ("Revert "net: core: maybe return -EEXIST in __dev_alloc_name"")
Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
 net/core/dev.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 01ee854454a8..0e0ba36eeac9 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1146,7 +1146,19 @@ 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);
+	BUG_ON(!net);
+
+	if (!dev_valid_name(name))
+		return -EINVAL;
+
+	if (strchr(name, '%'))
+		return dev_alloc_name_ns(net, dev, name);
+	else if (__dev_get_by_name(net, name))
+		return -EEXIST;
+	else if (dev->name != name)
+		strlcpy(dev->name, name, IFNAMSIZ);
+
+	return 0;
 }
 EXPORT_SYMBOL(dev_get_valid_name);
 
-- 
2.14.3