[yocto] per-image ROOTFS sizes

[Trevor Woerner]

On Wed, Dec 12, 2012 at 3:46 PM, Robert P. J. Day <rpjday at crashcourse.ca> wrote:
> so what happens if you try to set the appropriate variables above?

When Yocto creates a VMDK, it creates 2 partitions:
- an MSDOS partition for the syslinux stuff
- the ext{3,4} partition of your root image

When it then shmushes these two together into 1 file, it has to make
sure all the sizes are set correctly as per the information in the
disk's partition table. That's what all these calculations are doing
(I recognize it from similar work in my own scripts).

Personally I have my own approach that can use either LILO or syslinux
for booting x86 (it can also create bootable ARM images with the
appropriate uboot/mlo); neither of the x86 solutions require a
separate MSDOS partition. Hopefully I'll find some time to examine how
Yocto is doing things and perhaps integrate my own findings into the
broader project(?).

(please see https://github.com/twoerner/qemu-image-builder)

I believe Yocto calculates the sizes (using IMAGE_ROOTFS_SIZE) from
code in poky/meta/classes/image_types.bbclass, which is also run for
the VMDK's calculations too.