Re: [PATCH v2] mtd: implement proper partition handling

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Boris,

Boris Brezillon <boris.brezillon@collabora.com> wrote on Thu, 9 Jan
2020 20:13:55 +0100:

> On Thu, 9 Jan 2020 19:45:56 +0100
> Miquel Raynal <miquel.raynal@bootlin.com> wrote:
> 
> > Hi Richard,
> > 
> > Richard Weinberger <richard@nod.at> wrote on Thu, 9 Jan 2020 19:43:04
> > +0100 (CET):
> >   
> > > Miquel,
> > > 
> > > ----- Ursprüngliche Mail -----    
> > > >> What problem does this solve?
> > > >> ...beside of a nice diffstat which removes more than it adds. :-)      
> > > > 
> > > > It is much easier to escalade to the top most "master" device when
> > > > there are multiple levels of partitioning, which was not cleanly
> > > > described IMHO. Also it is already used in the MLC-in-pseudo-SLC-mode
> > > > series :)      
> > > 
> > > Ok. In fact I "found" this patch my looking at the SLC emulation patches.
> > >     
> > > >> > +static inline struct mtd_info *mtd_get_master(struct mtd_info *mtd)
> > > >> > +{
> > > >> > +	while (mtd->parent)
> > > >> > +		mtd = mtd->parent;
> > > >> > +
> > > >> > +	return mtd;
> > > >> > +}      
> > > >> 
> > > >> So, parent == master?      
> > > > 
> > > > top most parent (the one without parent) == master !
> > > >       
> > > >> 
> > > >> When I create a MTD ontop of UBI using gluebi, who will be parent/master?      
> > > > 
> > > > I don't really understand the issue here?      
> > > 
> > > Let's say I have mtd0 with an ubi and a volume "xxx". After enabling
> > > gluebi a new mtd1 will arrive on the system.
> > > The stacking is mtd0 -> ubi (volume xxx) -> mtd1.    
> > 
> > This is much clearer, thanks!
> >   
> > > Is now a relationship between mtd1 and mtd0?    
> > 
> > No there is none. 
> >   
> > > I'd expect mtd1's parent being mtd0.    
> > 
> > This would be a new feature, right? I don't think it is the case today.  
> 
> We definitely don't want mtd1 to appear as a partition of mtd0 in that
> case (blocks in mtd1 can't be mapped to blocks in mtd0 without the UBI
> layer being involved). Maybe it'd be clearer if we move the parent
> field to mtd_part and add an MTD_IS_PARTITION flag. Or maybe we can
> just choose a better name.

I prefer the name change. I think the current struct organization
is right. What do you suggest?


Thanks,
Miquèl

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