loader: Add boot hook for slot selection

[tomchy]

Add a bootloader hook to alter the logic of the active slot selection in Direct XIP modes.

[nordicjm]

this is not how common code should work, bootutil is a common file for any RTOS, any zephyr specific code goes in boot/zephyr, and there should be no checking of e.g. Kconfigs in common code

[tomchy]

this is not how common code should work, bootutil is a common file for any RTOS, any zephyr specific code goes in boot/zephyr, and there should be no checking of e.g. Kconfigs in common code

Is there a place for a code that is zephyr-specific, yet should be shared between the app and bootloader?

Honestly, I had an impression that the shared code/library problem is not fully resolved in the MCUboot ATM, so we are seeking for good ideas here 🙂

Side note: that's one of the reasons why this is a draft PR.

[nordicjm]

this is not how common code should work, bootutil is a common file for any RTOS, any zephyr specific code goes in boot/zephyr, and there should be no checking of e.g. Kconfigs in common code

Is there a place for a code that is zephyr-specific, yet should be shared between the app and bootloader?

Honestly, I had an impression that the shared code/library problem is not fully resolved in the MCUboot ATM, so we are seeking for good ideas here 🙂

Side note: that's one of the reasons why this is a draft PR.

Depends what it is, if it's zephyr centric then it can go into zephyr itself (e.g. boot mode is in zephyr and used in apps and mcuboot), I'm not sure what this code really does or what part is meant to be shared

[tomchy]

this is not how common code should work, bootutil is a common file for any RTOS, any zephyr specific code goes in boot/zephyr, and there should be no checking of e.g. Kconfigs in common code

Is there a place for a code that is zephyr-specific, yet should be shared between the app and bootloader?
Honestly, I had an impression that the shared code/library problem is not fully resolved in the MCUboot ATM, so we are seeking for good ideas here 🙂
Side note: that's one of the reasons why this is a draft PR.

Depends what it is, if it's zephyr centric then it can go into zephyr itself (e.g. boot mode is in zephyr and used in apps and mcuboot), I'm not sure what this code really does or what part is meant to be shared

Sine the boot request API is used by the bootutil logic, I decided to move it into the MCUBoot include directory.
That way the header is common, but the implementation is platform-specific (just like the security counter API).
There is still one Kconfig left: the CONFIG_MCUBOOT as it was already there for changing the implementation, based on the context (app vs bootloader). If there is a MCUboot-centric way to do that, let me know, I'll be happy to replace it.

If you agree on the current split, I'll add a note about the new configuration option inside the MCUboot docs.

[tomchy]

Scope reduced to the bootloader hook for the active slot selection.

[de-nordic]

Separate Zephyr and bootutil code into different commits.