Re: Old ATA disk names emulation [Was: Switch from legacy ata(4) to CAM-based ATA]

On Mon, Apr 25, 2011 at 03:26:02PM +0300, Alexander Motin wrote:
> Andrey V. Elsukov wrote:
> > On 25.04.2011 14:23, Alexander Motin wrote:
> >> What will not work:
> >>  - old device names won't be seen inside GEOM, so users who hardcoded
> >> provider names in gmirror/gstripe/... metadata (not the default
> >> behavior) are still in trouble.
> >>  - patch mimics ATA_STATIC_ID behavior, if user had custom kernel
> >> without it, he should update device names manually.
> >>  - it won't work for users with hot-unplugging ATA controllers (not
> >> devices), but I believe it is really rare case.
> >>  - low-level tools, such as smartmontools, won't be able to work with
> >> alias devices, as background ada driver doesn't implements legacy
> >> ioctls. May be I could partially fix this.
> >>
> >> Except those, I think this patch should work for the most of users.
> >>
> >> Any more objections/ideas? Is this an acceptable solution?
> > 
> > what about new GEOM class? You can create new class instance after
> > disk_alloc(), attach it to the new disk and create provider with old-style
> > name. It seems this class will be very simple.
> 
> It sounds like less dirty option. I'll try it. Thank you. Won't
> re-providing exactly the same device into GEOM create some problems?
> glabel and co will connect to each of them (original and legacy) and
> report two equal sets of labels.

Can you limit the real functionality of this new class to the calls
to make_dev_alias(9) ? Ideally, I would think about some extension of
the core GEOM, which would take some parameter, lets call it alias
name, and will acompany the existing make_dev() calls with parallel
make_dev_alias().