Re: [RFC] sysfs_rename_link() and its usage

On Tue, Jan 14, 2014 at 11:31:39AM -0800, Greg KH wrote:

On Tue, Jan 14, 2014 at 08:12:08PM +0100, Veaceslav Falico wrote:

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On Tue, Jan 14, 2014 at 10:21:35AM -0800, Greg KH wrote:

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On Tue, Jan 14, 2014 at 06:17:40PM +0100, Veaceslav Falico wrote:

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Hi,

I'm hitting a strange issue and/or I'm completely lost in sysfs internals.

Consider having two net_device *a, *b; which are registered normally.
Now, to create a link from /sys/class/net/a->name/linkname to b, one should
use:

sysfs_create_link(&(a->dev.kobj), &(b->dev.kobj), linkname);

To remove it, even simpler:

sysfs_remove_link(&(a->dev.kobj), linkname);

This works like a charm. However, if I want to use (obviously, with the
symlink present):

sysfs_rename_link(&(a->dev.kobj), &(b->dev.kobj), oldname, newname);

You forgot the namespace option to this call, what kernel version are
you using here?

It's git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next ,
3.13-rc6 with some networking patches on top of it.

And wrt namespace - there are two functions, one is sysfs_rename_link(),
which calls the second one - sysfs_rename_link_ns() with NULL namespace.

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this fails with:

"sysfs: ns invalid in 'a->name' for 'oldname'"

Looks like the namespace for this link isn't valid.

Yep, though dunno why.

Are you testing this with network namespaces enabled?  Perhaps that is
why, you need to specify the namespace of the link that you are
changing.

The fact that the bridge link works is odd to me, I would think that it
too needs to specify the network namespace involved, but perhaps bridge
objects aren't part of any specific network namespace?  I don't know the
bridging code at all, sorry.

Yep, might be it, will test soon and come back with the results.

What still bugs me, though, is the logic - why is it possible to remove/add
without specifying namespace, while it fails to rename it? Maybe the rename
function should do a better job at detecting the namespace?

So try calling sysfs_rename_link_ns() and specify the namespace of the
kobject you are changing, and see if that works or not.

thanks,

greg k-h