[OE-core] How to use WIC to generate raw flash images

[Ed Bartosh]

On Fri, Jan 20, 2017 at 10:37:15AM -0800, Rick Altherr wrote:
> For OpenBMC (based on Yocto), the target is an SoC that has an external
> boot flash connected via SPI.  Right now, we have a class (
> https://github.com/openbmc/openbmc/blob/master/meta-phosphor/classes/image-overlay.bbclass)
> used by our top-level image recipe (
> https://github.com/openbmc/openbmc/blob/master/meta-phosphor/common/recipes-phosphor/images/obmc-phosphor-image.bb)
> that manually constructs a flash image from the kernel, rootfs, etc.

This is indeed very interesting work. We definitely need support of flash images in oe-core.

> I'd like to move to an upstream-supported approach and I think that is WIC.

> What I don't understand is:
> - How do I build a raw flash image where it is divided into partitions but
> has no partition table?

Wic doesn't support this type of images, but it shouldn't be hard to add
option to skip partitioning to .wks syntax and wic code.

> - How do I set padding to be 0xFF instead of 0x00?
The same thing here. Currently wic images are sparse files created by
os.ftruncate, but it's not a big deal to fill them with 0xFF

> - How do I include u-boot in the image?

This can be done by using/extending rawcopy plugin or writing similar
one.

> Do I need to add a new imager plugin to support writing raw images with
> non-zero padding and no partition table?  For U-Boot, do I add a new
> bootimg plugin?

This sounds reasonable. Can you create a bug for this in bugzilla to discuss design and implementation details?

--
Regards,
Ed