Re: [PATCH] block: add command line partition parser

[Brian Norris]

On Thu, Aug 15, 2013 at 06:16:04AM +0000, Caizhiyong wrote:
> > -----Original Message-----
> > From: Brian Norris [mailto:computersforpeace@xxxxxxxxx]
> > Sent: Thursday, August 15, 2013 1:00 PM
> > To: Caizhiyong
> > Cc: Andrew Morton; Karel Zak; linux-mtd@xxxxxxxxxxxxxxxxxxx;
> > linux-kernel@xxxxxxxxxxxxxxx; Wanglin (Albert); Artem Bityutskiy; Shmulik Ladkani;
> > Huang Shijie
> > Subject: Re: [PATCH] block: add command line partition parser
> > 
> > On Thu, Aug 15, 2013 at 03:38:47AM +0000, Caizhiyong wrote:
> > > > -----Original Message-----
> > > > From: Brian Norris [mailto:computersforpeace@xxxxxxxxx]
> > > > Sent: Thursday, August 15, 2013 8:12 AM
> > > > To: Andrew Morton
> > > > Cc: Caizhiyong; Karel Zak; linux-mtd@xxxxxxxxxxxxxxxxxxx;
> > > > linux-kernel@xxxxxxxxxxxxxxx; Wanglin (Albert); Artem Bityutskiy; Shmulik
> > Ladkani;
> > > > Huang Shijie
> > > > Subject: Re: [PATCH] block: add command line partition parser
> > > >
> > > > On Wed, Aug 14, 2013 at 3:57 PM, Andrew Morton
> > > > <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > > > > On Tue, 13 Aug 2013 06:02:17 +0000 Caizhiyong <caizhiyong@xxxxxxxxxx> wrote:
> > > > >
> > > > >> move the command line parser to a separate module, and change it into
> > > > >> library-style code.
> > > > >>
> > > > >> reference: https://lkml.org/lkml/2013/8/6/550
> > > >
> > > > The most recent patch is an addendum to this linked patch then?
> > > >
> > > > > Well OK.  But to prove the library's usefulness and to generally clean
> > > > > up the kernel, someone needs to sign up to the task of converting
> > > > > drivers/mtd/cmdlinepart.c to use this code.
> > > > >
> > > > > I've been hopefully cc'ing various MTD people but am not being
> > > > > overwhelmed with waves of enthusiasm ;)
> > > >
> > > > "I've been" implies that you have done so prior to this email. And
> > > > "people" implies more than one person. I see that you CC'd David
> > > > Woodhouse over a week ago, but he's fairly silent these days on MTD
> > > > things. It's Artem or me who handle most of the day-to-day of MTD. And
> > > > this is the first time I've seen this! (BTW, please include
> > > > linux-mtd@xxxxxxxxxxxxxxxxxxx for anything involving MTD.)
> > > >
> > > > This seems reasonable, and I'd be willing to work with this proposal.
> > > >
> > > > Caizhiyong, can you submit a clear single patch (or series of
> > > > patches), CC'd to linux-mtd at least? Then we can see about supporting
> > > > it in MTD. It doesn't look too difficult, but I need to check that it
> > > > faithfully mimics the capability we currently rely on. There have been
> > > > previous discussions on changing it, but this was rejected in favor of
> > > > allowing more flexibility. Here's part of one such conversation:
> > > >
> > > > http://lists.infradead.org/pipermail/linux-mtd/2012-August/043599.html
> > > > http://lists.infradead.org/pipermail/linux-mtd/2012-September/043825.html
> > > > http://lists.infradead.org/pipermail/linux-mtd/2012-December/045322.html
> > > >
> > > > So I would recommend:
> > > > (1) consider carefully the implications of your command-line format
> > > > now, rather than later
> > > > (2) if you want MTD to use it, it needs to support the features we use now
> > >
> > > It is fully functional reference MTD, :-).
> > 
> > I realize that. I just want to be clear that we have to reconcile (1)
> > and (2). IOW, if block device requirements stray too far from MTD
> > requirements, then we might as well drop the idea of integration now.
> > But if they agree, then we can move forward.
> > 
> > > > Some particular cases to consider: overlapping partitions (how do
> > > > block devices handle overlapping partitions?), out-of-order
> > > > specification, zero sized partitions, mixed syntax (some specified
> > > > with an offset, some not), multiple '-' partitions.
> > >
> > > I think the 'offset' just is used to hide some MTD space.
> > 
> > No, it specifies offset as a distance from the beginning of the flash,
> > so partitions can be numbered out of order. This is intentionally
> > utilized by some users, for example, to ensure that a particular
> > partition is always /dev/mtd0, even if it is not the first partition
> > physically.
> > 
> > > There are two way:
> > > 1) redefine the 'offset' as a gap between forward partition and next partition.
> > > 2) add code forbid command line partitions overlapping and out-of-order.
> > >
> > > I recommend 1), it seems to solve those problem(overlapping and out-of-order),
> > but it will affect habit.
> > 
> > The linked discussion is where MTD settled on retaining old practice. I
> > brought it up not so that we change it here, but so that you would
> > understand what you are agreeing to if you adopt a common MTD and block
> > device parsing infrastructure.
> > 
> > [Note that I am much less familiar with block device mechanics than with
> > MTD.] Are any of the problem areas I mentioned actually forbidden on
> > block devices? I know, for instance, that an MBR partition table can
> > specify partitions out of order. And I've googled around and seen some
> > posts about people (unintentionally) ending up with overlapping hard
> > disk partitions.
> > 
> > So from my primitive knowledge, it sounds like a block devices parser
> > could agree with the same principle put forward by Shmulik in that
> > second URL:
> > 
> >  "So far, mtdparts commandline parsing has been very lenient and liberal.
> >   I think we should keep this approach; give the user the flexibility,
> >   he'll be responsible to provide meaningful cmdline parts for his
> >   system."
> > 
> > Brian
> 
> I want to use the MTD command line partition method on block devices (eMMC).
> It is very suitable for embedded systems. I think, in embedded system partition method,
> if somebody need some feature on MTD device, he may be also need it on block device.
> so I fully functional reference MTD command line partition.

I agree.

I'm curious: have you seen any need for a similar arrangement via
device-tree? See, for example, drivers/mtd/ofpart.c.

> I tested the out-of-order and overlapping on my system, used command line partition, It is work ok.
> The block device code is not make any restrictions on partition out-of-order and overlapping.

OK, good. Thanks for checking.

> I hope extend the flexibility to block device.

Sure. I'll try to review the full patch soon and test out integrating
it with MTD.

Thanks,
Brian
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