On Tuesday October 28, kay.sievers@xxxxxxxx wrote:
> On Tue, Oct 28, 2008 at 00:23, Neil Brown <neilb@xxxxxxx> wrote:
> > I notice that 'md'
> > devices don't seem to disappear. Maybe that is because /sys/block/mdX
> > never disappears (last time I tried it was too racy).
>
> It stays because the md kernel device lifetime rules are kind of
> broken regarding hotplug setups. Similar issue why md needs all the
> static nodes in /dev too to create a device.
>
> > Would there be any way to get udev to delete devices when
> > /sys/block/mdX/md/array_state
> > becomes 'clear' (presumably on a CHANGE event) ??
>
> What would be the reason to leave the kernel block device around?
> Can't you just remove it like any other subsytem in the kernel does.
> That would just remove the node, all links and update userspace to
> reflect the change.
>
> There is currently no "change" event that could tell to remove a
> device node in /dev while we still have a kernel device around. And
> you would need to convince me that this is really needed, and why md
> is so special here. :)
I've just done a bit of experimentation...
If create an array /dev/md0 and we get a symlink
/dev/disk/by-id/md-uuid-XXXXX -> ../../md0
I stop the array and the symlink stays there
I create a new array as /dev/md0 (hence new uuid)
and I get an new symlink
/dev/disk/by-id/md-uuid-YYYY -> ../../md0
but also, the first symlink goes away.
So somehow that first symlink is being removed even though the device
isn't being stopped.
I guess I need a
kobject_uevent(...., KOBJ_CHANGE)
when the array is stopped.... [tries that].
Better. But it looks like I need to get rid of the partitions too...
Yes. Putting
bdev = bdget_disk(mddev->gendisk, 0);
if (bdev) {
blkdev_ioctl(bdev, 0, BLKRRPART, 0);
bdput(bdev);
}
kobject_uevent(&disk_to_dev(mddev->gendisk)->kobj, KOBJ_CHANGE);
at a suitable place in do_md_stop causes all the symlinks created by
udev to disappear when I stop the array, only the /dev/mdX remains.
That should do for 2.6.28. Something better maybe for .29.
NeilBrown
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