netdev - Re: Is it normal to have cross namespace symlinks?

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Message-ID: <20140821191316.27807ef7@mad-cat.int.e5.ru>
Date:	Thu, 21 Aug 2014 19:13:16 +0400
From:	"Alexander Y. Fomichev" <git.user@...il.com>
To:	Veaceslav Falico <vfalico@...hat.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Is it normal to have cross namespace symlinks?

On Thu, 21 Aug 2014 14:12:05 +0200
Veaceslav Falico <vfalico@...hat.com> wrote:

> On Thu, Aug 21, 2014 at 02:38:16PM +0400, Alexander Y. Fomichev wrote:
> >Hello guys!
> >
> >Recently i switched to 3.14.x stable branch and i've got a bunch of
> >warnings:
> >
> >[   44.717746] ------------[ cut here ]------------
> >[   44.717750] WARNING: CPU: 1 PID: 7007 at fs/sysfs/dir.c:52
> >sysfs_warn_dup+0x86/0xa0() [   44.717751] sysfs: cannot create
> >duplicate filename
> >'/devices/pci0000:00/0000:00:1c.4/0000:05:00.0/net/eth1/upper_eth1'
> >
> >[   37.759856] ------------[ cut here ]------------
> >[   37.759863] WARNING: CPU: 1 PID: 3822 at fs/sysfs/dir.c:52
> >sysfs_warn_dup+0x86/0xa0() [   37.759864] sysfs: cannot create
> >duplicate filename '/devices/virtual/net/bond0/upper_eth0'
> >....
> >
> >It was triggered by renaming of macvlan interfaces in a freshly
> >created network namespaces. Just start two lxc containers one by one
> >with macvlans on the same lowerdev and rename devices inside
> >containers (with the same name) and voila.
> >v
> >I investigated problem a bit and i see that code in net/core/dev.c
> >which working with sysfs symlinks upper_dev / lower_dev is absolutely
> >unaware of namespaces. I mean code which uses functions
> >netdev_adjacent_sysfs_del,netdev_adjacent_sysfs_add
> >netdev_adjacent_rename_links,dev_change_name
> >just not takes into account that dev and adj_dev could be in a
> >different namespaces.
> 
> That's indeed so. When I've implemented it, I indeed didn't take into
> account net_ns, my bad.
> 
> Before the code, though, I'm not sure on how exactly to fix this. The
> only idea which comes to mind is to prohibit inter-net_ns symlinks
> (which can be done without much hassle) - i.e. to remove/add them on
> net_ns change, and to prohibit creating them on adding an inter-ns
> upper links.

uh.. seems like this is a first and only what come to mind. At least i
have something similar in my local tree. Though it looks pretty ugly and
required two ad-hoc functions traversing both adj_list(s). Though
again it works as expected in both directions so i attached it just in
case.

> However, as I definitely lack experience using net_ns, maybe there are
> other, better way, to fix this?

I can not say with confidence.. Someone of namespace guys better be
here.  as far as i can see the most notable thing in this context,
netdev belongs to only one net_ns at any one time and a little sense to
have a symlink on non-existent device.

-- 

Best regards.
        Alexander Y. Fomichev <Aleksandr.Fomichev@...ru>
	        +7-495-662-88-88 ext. 11346

View attachment "fix_netdev_adjacent_sysfs_links.patch" of type "text/x-patch" (3432 bytes)