Re: [RFC][Patch 0/3] Fix device_move() vs. dpm_list issues.

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Tue, 3 Mar 2009 09:55:27 -0500 (EST),
Alan Stern <stern@rowland.harvard.edu> wrote:

> On Tue, 3 Mar 2009, Ming Lei wrote:
> 
> > 2009/3/3 Cornelia Huck <cornelia.huck@de.ibm.com>:
> > > Hi,
> > >
> > > in thread [1], we discussed the issue of device_move() causing a
> > > reordering of devices without adapting the ancestral order in dpm_list.
> > > If a device is moved to a new parent that was registered after the
> > > device itself, it would still be after its new parent in dpm_list, thus
> > > causing the parent to be suspended before its child.
> > >
> > > This patchset attempts to remedy this situation by introducing an
> > > interface for a driver to manipulate dpm_list with the dpm_list_mtx
> > > held. (device_move() does not have enough information to do this
> > > manipulation itself.) The calling sequence for a driver would be:
> > >
> > > - lock the dpm_list
> > > - call device_move()
> > > - if device_move() succeeded, fix up dpm_list
> > > - unlock the dpm_list
> > 
> > IMHO, It is better to fix up dpm_list inside device_move() , like device_add(),
> > which may let s390, bluetooth or other possible users more happy with
> > device_remove().

Maybe I'm a bit dense today, but I don't understand the problem with
device_remove()?

> 
> I agree; it would be cleaner if device_move() could fix up dpm_list 
> directly.  If it doesn't have enough information to do so then change 
> the interface so that it does.  That should be pretty easy since there 
> are only a handful of callers.

The only really obvious one is 'move to NULL' -> 'move to end of
dpm_list'.
AFAICS, for that device_move() would need the following
parameters:
- device to be moved
- new parent
- which device to move in dpm_list (device, parent, or none)
and then still the moves I do in the s390 code don't seem obvious for
the driver core to get.

Given that the callers still need to specify what to do, I find it much
easier (and the resulting code much more understandable) if the callers
fix up dpm_list...