[U-Boot] what are valid formats for initrd image downloaded and used by "bootm"

[Wolfgang Denk]

Dear Robert,

In message <alpine.LFD.2.20.1607080453210.5437 at localhost.localdomain> you wrote:
> 
>   ok, and one last (admittedly a bit off-topic) followup ...
> openembedded supplies a class, image_types_uboot.bbclass, that can
> generate a pile of u-boot related images:
> 
> IMAGE_TYPES += "ext2.u-boot ext2.gz.u-boot ext2.bz2.u-boot
>    ext2.lzma.u-boot ext3.gz.u-boot ext4.gz.u-boot cpio.gz.u-boot"
> 
> if i want an immediately usable initrd i can download and pass off to
> bootm, i'm assuming i can use any of those "u-boot" suffixed image
> types, like, say, "cpio.gz.u-boot," which will generate a file with a
> name like "blahblah...20160708082958.rootfs.cpio.gz.u-boot".

What is your assumption based on?  Just on the suffix ".u-boot"?

>   so more an openembedded question, but am i correct in assuming that
> any of those OE "u-boot" files are usable as initrds? thanks.

You need to look into the actual recipes to be sure what the ".u-boot"
means, and how these images are built.

"openembedded-core/meta/classes/image_types_uboot.bbclass" defines
something like this:

oe_mkimage () {
    mkimage -A ${UBOOT_ARCH} -O linux -T ramdisk -C $2 -n ${IMAGE_NAME} \
        -d ${DEPLOY_DIR_IMAGE}/$1 ${DEPLOY_DIR_IMAGE}/$1.u-boot
    if [ x$3 = x"clean" ]; then
        rm $1
    fi  
} 

This would indeed mean that ".u-boot" is, from U-Boot's point of
view, a ramdisk image wrapped with the legacy image header, and as
such usable with "bootm".

Best regards,

Wolfgang Denk

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