Re: [RFC] sysfs_rename_link() and its usage

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

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

quoted

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.

quoted

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.

quoted

in

 608 struct sysfs_dirent *sysfs_find_dirent(struct sysfs_dirent *parent_sd,
...
 615         if (!!sysfs_ns_type(parent_sd) != !!ns) {
 616                 WARN(1, KERN_WARNING "sysfs: ns %s in '%s' for '%s'\n",
 617                         sysfs_ns_type(parent_sd) ? "required" : "invalid",
 618                         parent_sd->s_name, name);
 619                 return NULL;
 620         }

Code path:
warn_slowpath_fmt+0x46/0x50
sysfs_get_dirent_ns+0x30/0x80
sysfs_find_dirent+0x84/0x110
sysfs_get_dirent_ns+0x3e/0x80
sysfs_rename_link_ns+0x54/0xd0

I have no idea what this code means. Is there any reason for it to
fail (i.e. am I doing something wrong?) or I've hit a bug?

What exactly are you trying to do here?  Care to provide a pointer to
your code somewhere?

I've tried to handle the network device renames, ended up doing it with
sysfs_remove/add_link() calls. Patches:

http://patchwork.ozlabs.org/patch/310798/
http://patchwork.ozlabs.org/patch/310796/

If an upper device (say, vlan, bonding, bridge etc.) enslaves another
device, symlinks are created (given bridge0 and eth0):

/sys/class/net/eth0/upper_bridge0 -> ../bridge0
/sys/class/net/bridge0/lower_eth0 -> ../eth0

However, in case someone renames eth0/bridge0, these symlinks should also
be renamed, and sysfs_rename_link() should fit great here. But it fails.

quoted

I've tested the only user of it (bridge) - and it works fine, however it's
not using its own net_device's kobject but rather its own dir.

The driver core also uses this function, and it works there, so I'd
blame your code :)

Yeah, I'd also like to blame it, I'm afraid of touching anything
sysfs-related :).

thanks,

greg k-h