mdev accidently erases previously created nodes while trying to rename nodes

[Jean Wolter]

Denys Vlasenko <vda.linux at googlemail.com> writes:

> On Wed, Jun 17, 2009 at 3:52 PM, Jean Wolter<jw5 at os.inf.tu-dresden.de> wrote:
>> while using mdev to create device nodes for the capi subsystem mdev
>> accidently deletes a previously created node. Assume the following
>> lines in mdev.conf:
>>
>> capi            0:0 0660 =capi20
>> capi([0-9])     0:0 0660 =capi20.0%1
>> capi([0-9]*)    0:0 0660 =capi20.%1
>>
>> After loading the capi module the kernel generate a number of hotplug
>> events, starting with capi, followed by capi0-capi32. mdev creates
>> /dev/capi, and renames it to /dev/capi20.
>
> This seems to be ok.
>
>> When the event  "add tty /class/tty/capi0" comes in, mdev executes
>>
>>    unlink /dev/capi20
>>    mknod /dev/capi20
>>    rename(/dev/capi20,/dev/capi20.20)
>>
>> and erases the original /dev/capi20 device while doing this.
>
> This is the corresponding code:
>
>                 /* "Execute" the line we found */
>                 if (!delete && major >= 0) {
>                         if (ENABLE_FEATURE_MDEV_RENAME)
>                                 unlink(device_name);
>
> You say that /dev/capi20 is unlinked. Why? In event
> "add tty /class/tty/capi0" device_name == "capi0",
> thus unlink(device_name) won't delete "capi20". I'm confused.

You have every right to be confused. The events start with "add tty
/class/tty/capi0" up to /claas/tty/capi32. In the middle of this
sequence there is the event "add tty /class/tty/capi20"
device_name="capi20". busybox is configured with
ENABLE_FEATURE_MDEV_RENAME, so the first thing happens is an
unlink(device_name); in this case unlink("capi20").

regards,
Jean