[linux-lvm] Identifying useable block devices

Peter Rajnoha prajnoha at redhat.com
Fri Jan 24 13:29:55 UTC 2014

On 01/24/2014 02:24 PM, Peter Rajnoha wrote:
> On 01/23/2014 01:35 PM, Marius Vollmer wrote:
>> Peter Rajnoha <prajnoha at redhat.com> writes:
>>> On 01/22/2014 10:23 AM, Marius Vollmer wrote:
>>>> Is it guaranteed (modulo bugs) that the DM_UDEV_DISABLE_*_RULES flags
>>>> are only ever removed from a node, and are never added to it over it's
>>>> lifetime between add/remove events?
>>> No, we don't have this restriction generally
>> Ok.
>>>> This isn't true right now, and UDisks fails to handle it correctly
>>>> when a flag is added in a "change" event.  I am asking to figure out
>>>> where the fix should go.
>>> Well, udisks should always check the DM_UDEV_DISABLE_OTHER_RULES_FLAG
>>> and if it's set, skip its processing. It already has:
>>> # honor the flag that device-mapper sets if the device should be ignored
>>> ..in 80-udisks.rules. So it should be already following this.
>> That's from UDisks 1, I am concerned with UDisks2, which is a quite
>> different beast, I think.  Sorry for not making this clear.
>> The problem with UDisks2, as I see it, is that it ignores a "change" or
>> "add" event that has DM_UDEV_DISABLE_OTHER_RULES_FLAG set, while I think
>> it should treat it as a "remove" event.
>> I have proposed this patch:
>>     https://bugs.freedesktop.org/attachment.cgi?id=92577&action=edit
> Well, I don't quite agree with this statement from the patch:
>  "We treat the uevent as "remove" if the device-mapper layer
>   requests that other rules ignore this uevent".
> The flag (DM_UDEV_DISABLE_OTHER_RULES_FLAG) is here to direct
> udev processing to skip any scans - it's not actually saying
> everyone else should remove this device now. It's just saying
> "don't access/touch it" when this flag is set. If there was a
> situation where we really need to remove (deactivate) the device,
> we'd do that in lvm2 directly within processing of the device.

...simply, the event listener that gets the event with this flag
set should just consider this dm device as "private".


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