Re: net interface renaming issue (+fix?)

[Andrey Borzenkov <arvidjaar@mail.ru>]

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On Sunday 09 April 2006 21:21, Thomas de Grenier de Latour wrote:
> Hi,
>
> I'm running Gentoo Linux, a 2.6.16-ck kernel, and udev-0.89-r2, and
> have had hard time with network interfaces renaming through udev
> rules. The first thing i've tried were rules like this one:
>
> SUBSYSTEM="net", KERNEL="eth*", SYSFS{address}="00:0d:60:12:75:0a",
> NAME="lan"
>
> Plus this one from the standard early rules:
>
> ACTION="add", SUBSYSTEM="net", WAIT_FOR_SYSFS="address"
>
> It doesn't work when i "modprobe e1000" (my ethernet driver):
> ....
> udevd[21612]: udev_event_run: seq 956 forked, pid [21816], 'add' 'net', 0
> seconds old udevd-event[21816]: wait_for_sysfs: file
> '/sys/class/net/eth0/address' appeared after 0 loops udevd-event[21816]:
> udev_rules_get_name: no node name set, will use kernel name 'eth0' ....
> But if i later do a "echo add > /sys/class/net/eth0/uevent", then
> interface is properly renamed. It also works fine if i start with
> the module initialy not loaded, and then trigger the uevent on the
> corresponding pci device (will load the module, etc.)
>

There appears to be race between creating 'address' and getting (usable) 
value. See below.

[...]
>
> So i wonder, maybe such a rule should be added to the standard early
> ones? It should maybe use more checks though, to be sure there is
> actually a driver to wait. Something like ENV{PHYSDEVPATH}="?*"
> and/or ENV{PHYSDEVDRIVER}="?*".
>

You probably get reply that they are obsolete and should not be used in new 
rules :)
[...]
> Or is "address" being added to sysfs with no useful value yet the real
> issue, and my rule only an ugly workround?
>

Seems so.

net/core/net-syfs.c:dev_isalive():
        return dev->reg_state = NETREG_REGISTERED;

net/core/net-syfs.c:show_address():
        if (dev_isalive(net))
            ret = format_addr(buf, net->dev_addr, net->addr_len);

net/core/dev.c:netdev_run_todo():
                        err = netdev_register_sysfs(dev);
                        if (err)
                                printk(KERN_ERR "%s: failed sysfs registration 
(%d)\n",
                                       dev->name, err);
                        dev->reg_state = NETREG_REGISTERED;
                        break;

So basically there is a window between net device appearing in sysfs and 
'address' returning usable value. To test you could move dev->reg_state 
assignment before netdev_register_sysfs call; if this helps it makes sense 
ask on net list if this is safe change.

- -andrey
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