[v5,3/4] partitions/efi: add support for uImage.FIT sub-partitions

  Add new GUID allowing to parse uImage.FIT stored in a GPT partition
and map filesystem sub-image as sub-partitions.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
---
 block/partitions/efi.c | 9 +++++++++
 block/partitions/efi.h | 3 +++
 2 files changed, 12 insertions(+)
  

On Tue, Nov 15, 2022 at 09:47:06PM +0000, Daniel Golle wrote:
> Add new GUID allowing to parse uImage.FIT stored in a GPT partition
> and map filesystem sub-image as sub-partitions.

NAK, we should not go out from the partition code to parse random
weird image formats.  If you want to support uImage.FIT just write
a tinty stackable block driver or dm table for it.
  

Hi Christoph,

On Tue, Nov 15, 2022 at 10:01:05PM -0800, Christoph Hellwig wrote:
> On Tue, Nov 15, 2022 at 09:47:06PM +0000, Daniel Golle wrote:
> > Add new GUID allowing to parse uImage.FIT stored in a GPT partition
> > and map filesystem sub-image as sub-partitions.
> 
> NAK, we should not go out from the partition code to parse random
> weird image formats.

While weirdness is certainly subjective, uImage.FIT is not just a
random image format but used by a great majority of headless embedded
Linux devices out there. It's the default image format of many of the
SDKs distributed by chip vendors such as Allwinner, Marvell, MediaTek,
NXP, Qualcomm/Atheros, ...

Having better support for it in Linux hence doesn't seem too far-fetched
to me, especially given that we got partition parsers for all sorts of
historic (Acorn, Amiga, Atari, ...) or actually exotic (Karma?) formats.
Even Microsoft Windows' Logical Disk Manager is supported natively by
the kernel...

> If you want to support uImage.FIT just write a tiny stackable block
> driver or dm table for it.

As this is used on rather tiny embedded devices my hope was to keep
things simple and not having to enable device mapper on systems which
have anyway only very small amounts of storage and won't ever need
most of the device mapper features.

Using a tiny block driver instead is an option, I've implemented this
approach in the past couple of hours and it works just as fine.

In this case I would introduce a new kernel cmdline option allowing
to specify which block device (ie. a partition on eMMC, or mtdblock
or ubiblock device) to launch the uImage.FIT parser on.

Allowing this new driver to add block partitions by exporting a new
helper functions for that in block/partition/core.c would greatly
simplify things, as then the existing partitioning code could still
be used (instead of basically having to re-implement loopdev and
introduce a whole new type of block devices).

I will post an RFC series illustrating this approach.

Please let me know if this sounds acceptable, so I won't put effort
into implementing something which will then be rejected again after 5
iterations on the mailing list for reasons which could have been
expressed from the beginning. An RFC for this series was posted on
2022-04-25 [1], I wouldn't have worked months to fix all requests of
other maintainers and tested it on a variety of different hardware
knowing that the whole approach will be NACK'ed...

And, of course, thank you anyway for reviewing!


Cheers


Daniel

[1]: https://patchwork.kernel.org/project/linux-block/list/?series=635369&state=*
  

On Thu, Nov 17, 2022 at 12:19:10AM +0000, Daniel Golle wrote:
> While weirdness is certainly subjective, uImage.FIT is not just a
> random image format but used by a great majority of headless embedded
> Linux devices out there. It's the default image format of many of the
> SDKs distributed by chip vendors such as Allwinner, Marvell, MediaTek,
> NXP, Qualcomm/Atheros, ...

"Look see, my weird format is used by all these companies building
crappy SOCs, it is not weird.."

> Please let me know if this sounds acceptable, so I won't put effort
> into implementing something which will then be rejected again after 5
> iterations on the mailing list for reasons which could have been
> expressed from the beginning. An RFC for this series was posted on
> 2022-04-25 [1], I wouldn't have worked months to fix all requests of
> other maintainers and tested it on a variety of different hardware
> knowing that the whole approach will be NACK'ed...

If people ignore something that is obviously broken they might just hope
for it to go away, becaue often it does.
  

----- Ursprüngliche Mail -----
> Von: "Christoph Hellwig" <hch@infradead.org>
> On Thu, Nov 17, 2022 at 12:19:10AM +0000, Daniel Golle wrote:
>> While weirdness is certainly subjective, uImage.FIT is not just a
>> random image format but used by a great majority of headless embedded
>> Linux devices out there. It's the default image format of many of the
>> SDKs distributed by chip vendors such as Allwinner, Marvell, MediaTek,
>> NXP, Qualcomm/Atheros, ...
> 
> "Look see, my weird format is used by all these companies building
> crappy SOCs, it is not weird.."

Well, FIT is not something strange invented by SoC companies, it comes from u-boot
and is more or less a de-facto standard.
While I agree that using the block layer for partition parsing is questionable
I think supporting these images in Linux is a worthwhile goal.

Thanks,
//richard
  

On Thu, Nov 17, 2022 at 07:50:08AM +0100, Richard Weinberger wrote:
> I think supporting these images in Linux is a worthwhile goal.

I never argued against that.  But it is not a fit for partitions.
So write a proper stacked block driver or dm driver for it if you
care enough.  The format is a complete mess and should be isolated
to not affect the rest of the kernel.
  

On Wed, Nov 16, 2022 at 10:00:25PM -0800, Christoph Hellwig wrote:
> On Thu, Nov 17, 2022 at 12:19:10AM +0000, Daniel Golle wrote:
> > While weirdness is certainly subjective, uImage.FIT is not just a
> > random image format but used by a great majority of headless embedded
> > Linux devices out there. It's the default image format of many of the
> > SDKs distributed by chip vendors such as Allwinner, Marvell, MediaTek,
> > NXP, Qualcomm/Atheros, ...
> 
> "Look see, my weird format is used by all these companies building
> crappy SOCs, it is not weird.."

I didn't invent this, and it's just as broken and yet perdominant as,
let's say, MS LDM on x86.

> 
> > Please let me know if this sounds acceptable, so I won't put effort
> > into implementing something which will then be rejected again after 5
> > iterations on the mailing list for reasons which could have been
> > expressed from the beginning. An RFC for this series was posted on
> > 2022-04-25 [1], I wouldn't have worked months to fix all requests of
> > other maintainers and tested it on a variety of different hardware
> > knowing that the whole approach will be NACK'ed...
> 
> If people ignore something that is obviously broken they might just hope
> for it to go away, becaue often it does.

While I'm sure that strategy works seen from your perspective, it does
waste resources on the other end. In this case it might not have been
obvious to everybody, I did receive feedback from other maintainers,
as I said. It's not that everybody ignored this contribution. Hence,
looking at it from my end, the picture is a bit different. Anyway.
I would have appreciated an earlier explicite NACK, that's all I
wanted to say.