general: document f2fs cleanup; NO_SYNC non-default

AGENTS.md

@@ -13,7 +13,7 @@ Three repos cooperate:
 | `rubenslte/android_kernel_samsung_rubenslte` | Samsung msm8226 stock kernel, built from source |
 
 This drive builds from **source**: kernel, dt.img and ramdisk are all produced,
-never prebuilt. The artifact is `recovery.img` (currently 10,407,952 bytes,
+never prebuilt. The artifact is `recovery.img` (currently 10,366,992 bytes,
 TWRP 3.7.0_9-0) and has passed on-device tests on real hardware.
 
 ## Commands
@@ -56,7 +56,9 @@ Verification without nix (cheap): `bash -n build_twrp.sh`.
   the image under the 10,485,248-byte partition. Changing compression or adding
   `twres/`/`system/` files can overflow it — always re-check image size.
 - **F2FS is off.** The kernel has no F2FS driver. Never re-add
-  `TARGET_USERIMAGES_USE_F2FS`.
+  `TARGET_USERIMAGES_USE_F2FS`. `mkbootimg.mk` also deletes the f2fs tools from
+  the ramdisk (the format menu hides the option automatically when
+  `/sbin/mkfs.f2fs` is absent — see `gui/action.cpp:944` in the omni tree).
 - **dt.img is EUR-only** (`CONFIG_MACH_RUBENSLTE_OPEN`). Other hardware
   variants (T365Y/AUS, T365M/KOR) need their `CONFIG_MACH_RUBENSLTE_*`
   enabled + rebuild.
@@ -70,6 +72,10 @@ Verification without nix (cheap): `bash -n build_twrp.sh`.
   has no Android root. Mount System in TWRP, or use the in-TWRP terminal.
 - `make: ... [/dt.img] Błąd 255` — the lazy-variable/`INSTALLED_KERNEL_TARGET`
   dependency is broken; restore it per the invariants above.
+- f2fs tools reappear in the ramdisk — stale copies under
+  `out/target/product/rubenslte/root/sbin/` from a past f2fs-enabled build; the
+  core recovery rule `cp -R`s that directory without wiping. Delete the
+  binaries (and `recovery/root.ts`); `mkbootimg.mk` strips them anyway.
 - Multi-variant boot failures — dt.img lacks the device's DTB; rebuild with the
   right `CONFIG_MACH_RUBENSLTE_*`.
 

README.md

@@ -48,26 +48,25 @@ much faster. The final artifact is `recovery.img` at the repo root.
    selects the right one for the hardware.
 7. **Recovery ramdisk** — the stock minigzip ramdisk overflows the 10,485,248
    byte partition, so `mkbootimg.mk` replaces the core ramdisk rules: drops
-   tzdata, keeps only `en.xml`/`pl.xml` languages, and compresses with LZMA
-   (`CONFIG_RD_LZMA=y` in the rubenslte kernel).
+   tzdata and the f2fs tools, keeps only `en.xml`/`pl.xml` languages, and
+   compresses with LZMA (`CONFIG_RD_LZMA=y` in the rubenslte kernel).
 
-Image layout of the shipped `recovery.img`:
+Image layout of the shipped `recovery.img` (verified component sizes; exact
+offsets are 2048-byte aligned by the bootloader):
 
 ```
-offset        size        content
-0               2,048     boot image header (base 0x0, pagesize 2048)
-2,048       7,223,736    zImage (kernel)
-7,225,744       1,608     padding
-7,227,352     2,882,224   ramdisk, LZMA-compressed (gzip would overflow)
-10,109,576      1,360     padding
-10,110,936      296,960   dt.img (QCDT: two EUR dtbs, r02+r03)
-10,407,896         56     SEANDROIDENFORCE trailer
+boot image header (base 0x0, pagesize 2048)
+zImage               7,223,736   kernel
+ramdisk              2,841,269   LZMA-compressed (gzip would overflow)
+dt.img                 296,960   QCDT: two EUR dtbs, r02 + r03
+SEANDROIDENFORCE trailer
+total               10,366,992   fits the 10,485,248 byte partition
 ```
 
 Artifact facts:
 
-- `recovery.img` — 10,407,952 bytes (fits the 10,485,248 byte partition)
-- sha256 `add52ab4d7ccbedd24ad08a89fe075c3cf918646bf6e77c6d610bcabd86a6b5b`
+- `recovery.img` — 10,366,992 bytes (fits the 10,485,248 byte partition)
+- sha256 `cf8c711afeb5636f6b01ee253d0643d380f127e7e71e8c1d3a163a148ab97703`
 - TWRP **3.7.0_9-0**, Linux kernel 3.4.x from Samsung source, built for
   Android 5.1.1 (omni twrp-5.1)
 
@@ -91,8 +90,12 @@ image dumped from the device; flash it back to restore the factory recovery.
   so dt.img carries only the two EUR DTBs (r02/r03). SM-T365Y (AUS) / SM-T365M
   / KOR units need the corresponding `CONFIG_MACH_RUBENSLTE_*` enabled and a
   rebuild, otherwise the device may not boot from this kernel.
-- **`/data` is ext4.** The kernel has no F2FS driver, so do not format `Data`
-  as F2FS in TWRP. The `TARGET_USERIMAGES_USE_F2FS` flag is deliberately unset.
+- **`/data` is ext4, no F2FS.** The kernel has no F2FS driver, so the f2fs
+  tools are excluded (`TARGET_USERIMAGES_USE_F2FS` unset in BoardConfig.mk, and
+  `mkbootimg.mk` deletes them from the ramdisk defensively — they can linger in
+  `out/.../root/sbin/` from older f2fs-enabled builds). TWRP's format menu only
+  offers F2FS when `/sbin/mkfs.f2fs` is present, so the option is hidden
+  automatically. Do not format `Data` as F2FS.
 - **`adb shell` needs `/system` mounted.** `adb` itself works in recovery, but
   the device-side shell is `/system/bin/sh`; until you check **Mount → System**
   in TWRP you'll see `CANNOT LINK EXECUTABLE DEPENDENCIES: library "libc.so"
@@ -106,6 +109,10 @@ image dumped from the device; flash it back to restore the factory recovery.
   absolute base path. Don't "simplify" them to `:=`.
 - Image won't fit the partition — the ramdisk must stay LZMA and trimmed;
   re-check `mkbootimg.mk` if you add files under `twres/` or `system/`.
+- `mkfs.f2fs` reappears in the ramdisk after a rebuild — stale copy in
+  `out/target/product/rubenslte/root/sbin/` (the core rule `cp -R`s the boot
+  root into the recovery root without wiping it first). Delete them and
+  `recovery/root.ts`; `mkbootimg.mk` strips them from the packed image anyway.
 - `nix-shell --run ...` produces no output — known limitation of the
   `exec android-env` shellHook; use `./build_twrp.sh` or `./build_twrp.sh env`.
 - Parallel `nix-shell` invocations can deadlock on the nix store — run builds

build_twrp.sh

@@ -101,7 +101,7 @@ do_build() {
     if [ ! -d .repo ]; then
         repo init --depth 1 -u "$MANIFEST_URL" -b "$MANIFEST_BRANCH"
     fi
-    if [ -z "${NO_SYNC:-}" ]; then
+    if [ "$NO_SYNC" -eq 0 ]; then
         repo sync -c -j"$(nproc)"
         clone_or_update "device tree" "$DEVICE_TREE_URL" device/samsung/rubenslte
         clone_or_update "kernel" "$KERNEL_URL" kernel/samsung/rubenslte