Re: [dm-devel] [mdadm PATCH 4/4] Create: tell udev device is not ready when first created.

[Jes Sorensen <jes.sorensen@gmail.com>]

On 05/02/2017 07:40 AM, Peter Rajnoha wrote:
> On 05/01/2017 06:35 AM, NeilBrown wrote:
>> On Fri, Apr 28 2017, Peter Rajnoha wrote:
>>> Then mdadm opens the devive, clears any old content/signatures the data
>>> area may contain, then closes it - this generates the third event -
>>> which is the "synthetic change" event (as a result of the inotify WATCH
>>> rule). And this one would drop the "not initialized" flag in udev db and
>>> the scans in udev are now enabled.
>>
>> Nope, it would be incorrect for mdadm to clear any old content.
>> Sometimes people want to ignore old content.  Sometimes they very
>> definitely want to use it.  It would be wrong for any code to try to
>> guess what is wanted.
>
> The mdadm is not going to guess - it can have an option to
> enable/disable the wiping on demand directly on command line (which is
> also what is actually done in LVM).

I know the anaconda team keeps pushing for the nonsense of being able to 
wipe drives on creation. It is wrong, it is broken, and it is not going 
to happen.

> Otherwise, if mdadm is not going to wipe/initialize the device itself,
> then it needs to wait for the external tool to do it (based on external
> configuration or on some manual wipefs-like call). So the sequence would be:
>
>  1) mdadm creating the device
>  2) mdadm setting up the device, marking it as "not initialized yet"
>  4a) mdadm waiting for the external decision to be made about wiping part
>  4b) external tool doing the wiping (or not) based on configuration or
> user's will
>  5) mdadm continuing and finishing when the wiping part is complete
>
> I expect mdadm to return only if the device is properly initialized
> otherwise it's harder for other tools called after mdadm to start
> working with the device - they need to poll for the state laboriously
> and check for readiness.

What defines readiness? Some believe a raid1 array must be fully 
assembled with all members, other setups are happy to have one running 
drive in place.....

4a/4b in your list here once again has no place in mdadm. Please kindly 
tell the anaconda team to go back and handle this properly instead.

Jes