sysupgrade: say what --kernel, --rootfs, -k and -r take on each layout

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The help said --kernel takes a uImage and --rootfs a squashfs. That is only part of it:

• --kernel also takes a FIT (cv6xx), or zboot.img on Rockchip.
• On a UBIFS NAND camera (root=ubi0:rootfs, the layout from nand: kernel inside the UBIFS rootfs, volumes sized by their images; retire the old NAND layouts #2537) the rootfs is rootfs.ubifs and carries the kernel. -k and -r both write it, and --kernel on its own is refused with a pointer to --rootfs.

The help now says so. Help text only; no behaviour changes.

sh -n passes, and .github/scripts/test_sysupgrade.sh passes on top of #2538.

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PR Summary by Qodo

Clarify sysupgrade image formats by device layout

📝 Documentation 🕐 Less than 10 minutes

AI Description

• Clarifies that kernel files may be uImage, FIT, or Rockchip zboot.img images.
• Explains that UBIFS NAND cameras use rootfs.ubifs for both online update flags and require
 --rootfs for local files.
• Changes help text only; upgrade behavior is unchanged.

Diagram

graph TD
  Help["sysupgrade help"] --> Remote["Online flags"] --> Layout{"UBIFS NAND?"} -->|Yes| UBIFS["rootfs.ubifs only"]
  Help --> Local["Local file flags"] --> Layout -->|No| Standard["Platform image formats"]

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High-Level Assessment

Updating the existing usage text is appropriate for a documentation-only correction. Changing upgrade logic or adding separate layout-specific help paths would add complexity without addressing a behavior defect.

Files changed (1) +7 / -2

Documentation (1) +7 / -2

sysupgradeDocument layout-specific sysupgrade image requirements +7/-2

Document layout-specific sysupgrade image requirements

• The usage text now lists uImage, FIT, and Rockchip zboot.img kernel formats. It also explains that UBIFS NAND cameras use rootfs.ubifs for both online flags and require --rootfs, rather than --kernel, for a local image.

general/overlay/usr/sbin/sysupgrade