External Flash Sample Issue

After some playing around, here is some findings:

Flashing the device with bootloader: v2-010421-1502-merged.hex, https://docs.jaredwolff.com/nrf9160-downloads.html, and flash via newtmgr app_update.bin, I experiencing the following

*** Booting Zephyr OS build v2.6.99-ncs1-1  ***
Area 1 at 0x0 on W25Q32JV for 4194304 bytes
[00:00:00.217,407] <inf> littlefs: LittleFS version 2.2, disk version 2.0
[00:00:00.225,067] <dbg> littlefs.littlefs_mount: FS area 1 at 0x0 for 4194304 bytes
[00:00:00.234,649] <inf> littlefs: FS at W25Q32JV:0x0 is 1024 0x1000-byte blocks with 512 cycle
[00:00:00.244,232] <inf> littlefs: sizes: rd 16 ; pr 16 ; ca 64 ; la 32
[00:00:00.252,471] <inf> littlefs: /lfs mounted
[00:00:00.257,629] <dbg> fs.fs_mount: fs mounted at /lfs
/lfs mount: 0
/lfs: bsize = 16 ; frsize = 4096 ; blocks = 1024 ; bfree = 1022
/lfs/boot_count stat: -2
FAIL: open /lfs/boot_count: -16
[00:00:00.277,832] <inf> littlefs: /lfs unmounted
[00:00:00.283,233] <dbg> fs.fs_unmount: fs unmounted from /lfs
/lfs unmount: 0

If build and flash the whole app hex directly from the samples, I experience the following:

*** Booting Zephyr OS build v2.6.99-ncs1-1  ***
Area 1 at 0x0 on W25Q32JV for 4194304 bytes
[00:00:00.217,376] <inf> littlefs: LittleFS version 2.2, disk version 2.0
[00:00:00.225,036] <dbg> littlefs.littlefs_mount: FS area 1 at 0x0 for 4194304 bytes
[00:00:00.234,558] <inf> littlefs: FS at W25Q32JV:0x0 is 1024 0x1000-byte blocks with 512 cycle
[00:00:00.244,140] <inf> littlefs: sizes: rd 16 ; pr 16 ; ca 64 ; la 32
[00:00:00.260,589] <inf> littlefs: /lfs mounted
[00:00:00.265,716] <dbg> fs.fs_mount: fs mounted at /lfs
/lfs mount: 0
/lfs: bsize = 16 ; frsize = 4096 ; blocks = 1024 ; bfree = 1019
/lfs/boots_count stat: 0
        fn 'boots_count' siz 4
/lfs/boots_count read count 8: 4
/lfs/boots_count seek start: 0
/lfs/boots_count write new boot count 9: 4
/lfs/boots_count close: 0
Settings: before: status 8, interval: 20
Settings: after: status 9, interval: 20
[00:00:00.550,140] <inf> littlefs: /lfs unmounted
[00:00:00.555,450] <dbg> fs.fs_unmount: fs unmounted from /lfs
/lfs unmount: 0

but the device will no longer run on battery as described here https://community.jaredwolff.com/d/326-ps-en-pin-enabled-in-bootloader-during-boot

The bootloader in the project dir is commit b514a3190821b7721dd6ffcd9940474ebe7a8832 (HEAD, tag: v1.7.99-ncs3-1, tag: v1.7.99-ncs3, manifest-rev)

After comparing against the zephyr samples, it appears the root cause here is a missing call fs_file_t_init(&file); prior to opening the file. This would leave the struct uninitialized and cause undefined behavior.

static inline void fs_file_t_init(struct fs_file_t *zfp)
{
	*zfp = (struct fs_file_t){ 0 };
}

I am no longer experiencing issues after adding this function call and appears to be required as stated in the documentation.

https://github.com/circuitdojo/nrf9160-feather-examples-and-drivers/blob/v1.9.x/samples/external_flash/src/main.c#L142
https://docs.zephyrproject.org/latest/services/file_system/index.html#c.fs_file_t_init