Failing to create a directory

[sseoud]

Hi, We are using littleFs with the following configuration truct lfs_config cfg = { // block device configuration .read_size = 16, .prog_size = 256, .block_size = 4096, .block_count = 8, .cache_size = 256, .lookahead_size = 16, .block_cycles = 500 }; We are using the internal flash of the mcu. I am trying to create 4 directories. the first 3 are created successfully while the last on failing with error code -28 Now if I change the block_count to 16 then all the directories are created and everything is fine. Can anyone please help me understand we I need to much space to create these directories Thanks in advance

[geky]

Hi @sseoud,

In the current design of littlefs, each directory gets its own metadata log. Each metadata log takes at minimum two blocks, so each directory needs 2 blocks. This includes the root.

(1 root + 4 directories)*2 = 10 blocks, so that would be why you see LFS_ERR_NOSPC (-28) when trying to create the last directory.

Using many directories with internal flash may not be a great fit in littlefs. It may make more sense to prefix files with application-specific prefixes as a part of the filename if you're only dealing with a handful of blocks.

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It's not helpful, but I thought worth noting I have some plans in the works to remove this strict dir <-> log relationship. But it will take some time before it's usable since it's a part of some larger changes.

[sseoud]

Hi @geky, Thanks for the answer. Is there a minimum requirement for the block size ? If I set the block size to 256 (the smallest erasable size in my internal flash), I can't format the device. Regards

[geky]

Hi @sseoud, sorry for the late response,

There is a fundamental limit at 128 bytes (assert here). But littlefs also expects file/superblock metadata to fit in a single block. When you go below ~512 bytes this gets a bit iffy and isn't well tested.

You can try using smaller filenames or custom attributes, though I would expect NOSPC/RANGE/NAMETOOLONG errors if that is the issue.

I would also double check the erase size, 256 bytes is a bit surprising for flash, and the chip may have other requirements to use the smaller erase size. Out of curiosity are you able to share which chip you are using?