[PATCH 1/2] node_device_udev: handle move events

Martin Kletzander mkletzan at redhat.com
Sat Apr 18 13:25:57 UTC 2020

On Thu, Apr 16, 2020 at 11:57:45AM -0400, Mark Asselstine wrote:
>It is possible and common to rename some devices, this is especially
>true for ethernet devices such as veth pairs.
>In the udevEventHandleThread() we will be notified of this change but
>currently we only process "add", "change" and "remove"
>events. Renaming a device such as above results in a "move" event, not
>a "remove" followed by and "add" or vise versa. This change will add
>the new/destination device to our records but unfortunately there is
>no usable mechanism to identify the old/source device to remove it
>from the records. So this is admittedly only a partial fix.

There is, but it is only internal.  We should ask for the function
`udev_device_get_devpath_old()` to be publicized, if possible.  That should give
us the old name.

When I checked this using `udevadm monitor --property` I got two events for each
rename, one kernel event (where the old path pointed to the previous name) and
one udev event where the old path referred to the original name the device was
created with.

For example when I created a virtual network device with the name "fdsa", then
renamed it bunch of times, started udev monitoring and then renamed it from
"first" to "second" this was the output of udevadm for that one particular rename:

monitor will print the received events for:
UDEV - the event which udev sends out after rule processing
KERNEL - the kernel uevent

KERNEL[36343.246068] move     /devices/virtual/net/second (net)

UDEV  [36343.246785] move     /devices/virtual/net/fdsa (net)

Thank you for a patch like this, I did not want to change the error just because
"it's probably fine" until I can be sure that we do not lose the device (even
though someone else is clearly managing it).

So I think the patches are great, and as much as I would like to add support for
removing the old device if possible, probably using the function above, it will
need some extra work.  At least we should file a request for the udev function
to be exposed.

Anyway, I am not against these patches and I would even be fine with changing
the warning to info in 2/2, but I will wait for someone else to see this and
comment (and I'd like to know your opinion on what I wrote as well).  If that
does not happen, I will retest them against (at that point) current master and
push them.

Reviewed-by: Martin Kletzander <mkletzan at redhat.com>

>Signed-off-by: Mark Asselstine <mark.asselstine at windriver.com>
> src/node_device/node_device_udev.c | 5 +++++
> 1 file changed, 5 insertions(+)
>diff --git a/src/node_device/node_device_udev.c b/src/node_device/node_device_udev.c
>index 8451903e8a..3149de8321 100644
>--- a/src/node_device/node_device_udev.c
>+++ b/src/node_device/node_device_udev.c
>@@ -1499,6 +1499,11 @@ udevHandleOneDevice(struct udev_device *device)
>     if (STREQ(action, "remove"))
>         return udevRemoveOneDevice(device);
>+    if (STREQ(action, "move")) {
>+        /* TODO: implement a way of finding and removing the old device */
>+        return udevAddOneDevice(device);
>+    }
>     return 0;
> }
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