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A/B and abctl Verification

abctl is a diagnostic and factory test tool for OTA A/B metadata. It can operate on regular files or /dev/block/by-name/misc on devices.

Metadata Convention​

  • A/B metadata is located at misc partition byte offset 2048.
  • Data structure is 32 bytes, compatible with Android AVB A/B layout version 1.0.
  • CRC32 uses big-endian IEEE, covering metadata bytes 0..27.
  • Reserved bytes remain reserved. Application OTA state is saved on the dedicated partition mounted at /userdata/ota, not written to misc reserved bytes.
  • Factory misc.img initial state: slot A priority 15, successful; slot B disabled.

Host Image Check​

Use regular files for safe testing:

build/bin/abctl init /tmp/misc.img --size 4M
build/bin/abctl read /tmp/misc.img

Expected output includes slot A successful, slot B priority 0, last_boot=A.

Manual state switching:

build/bin/abctl set-active /tmp/misc.img b --tries 3
build/bin/abctl read /tmp/misc.img
build/bin/abctl mark-successful /tmp/misc.img b
build/bin/abctl read /tmp/misc.img

Explicitly write test state:

build/bin/abctl write /tmp/misc.img \
  --a-priority 14 --a-tries 0 --a-successful 1 \
  --b-priority 15 --b-tries 3 --b-successful 0
build/bin/abctl read /tmp/misc.img

abctl write will reject illegal states, such as a successful slot with non-zero tries.

Device Check​

Read real misc on device:

/oem/usr/bin/abctl read /dev/block/by-name/misc

Manually switch slot:

/oem/usr/bin/abctl set-active /dev/block/by-name/misc b --tries 3
sync
reboot

After boot, confirm active slot:

cat /proc/cmdline
mount | grep ' /oem '
/oem/usr/bin/abctl read /dev/block/by-name/misc

After confirming device health, commit slot:

/oem/usr/bin/abctl mark-successful /dev/block/by-name/misc b
sync

Rollback Test​

Set up a trial boot and do not mark successful:

/oem/usr/bin/abctl set-active /dev/block/by-name/misc b --tries 1
sync
reboot

Do not commit B. Continue rebooting until SPL exhausts tries and returns to the previous successful slot. Confirm with cat /proc/cmdline, mount | grep ' /oem ', and abctl read.

Expected Diagnostic Signals​

  • /proc/cmdline contains aiden.slot_suffix=_a or _b.
  • root=PARTLABEL=rootfs_a|rootfs_b in /proc/cmdline matches slot suffix.
  • /oem is mounted from /dev/block/by-name/oem_a or oem_b, matching slot suffix.
  • abctl read can parse AVB A/B metadata without CRC or layout errors.
  • ota status can display OTA state, active slot, pending boot, and raw A/B data.