Re: net device renaming 2-step, IFNAMSIZ limit

[Piter PUNK <piterpunk@unitednerds.org>]

Matt Domsch wrote:
> I see this in the udev debug logs when using biosdevname (which I
> finally got working with SR-IOV devices tonight):
>
> renamed network interface eth60 to eth60-pci2#0_60
> renamed network interface eth60-pci2#0_60 to pci2#0_60
>
> So, it worked, however, note that the rename happens in 2 steps, the
> middle step of which uses a name that's dangerously close to
> IFNAMSIZ, in fact it is 15 chars there.
>
> <...>
>
> I need a solution in which the intermediate name doesn't exceed 15
> characters, and is guaranteed to be unique, as there may be lots of
> udev instances running in parallel trying to do the same thing.
>
> Ideas?

As we talk on #udev, there is a patch that uses hash32 function inside 
libudev to create
the intermediate name. We use the "oldname-newname" to create the hash. 
With that,
exceeding IFNAMSIZ isn't a problem:

-------cut here--------

diff --git a/udev/udev-event.c b/udev/udev-event.c
index 0648735..fc4aae0 100644
--- a/udev/udev-event.c
+++ b/udev/udev-event.c
@@ -462,6 +462,7 @@ static void rename_netif_kernel_log(struct ifreq ifr)
  static int rename_netif(struct udev_event *event)
  {
         struct udev_device *dev = event->dev;
+       char iftmp[IFNAMSIZ*2+1];
         int sk;
         struct ifreq ifr;
         int loop;
@@ -492,7 +493,8 @@ static int rename_netif(struct udev_event *event)
                 goto out;

         /* free our own name, another process may wait for us */
-       util_strscpyl(ifr.ifr_newname, IFNAMSIZ, 
udev_device_get_sysname(dev), "-", event->name, NULL);
+       util_strscpyl(iftmp, IFNAMSIZ*2+1, udev_device_get_sysname(dev), 
"-", event->name, NULL);
+       util_strscpyl(ifr.ifr_newname, IFNAMSIZ, "eth_%X", 
util_string_hash32(iftmp), NULL);
         err = ioctl(sk, SIOCSIFNAME, &ifr);
         if (err < 0) {
                 err = -errno;

-------cut here--------

Ideas and fixes are welcome,

Piter PUNK