Littlefs: limitation when no dynamic memory allocation is used

[husigeza]

Hello,

Could you help me regarding what limitations exist when statically allocated buffers are passed to the configuration structure instead of using dynamic memory allocation ?

Above the "file_buffer" it writes: "If enabled, only one file may be opened at a time." -> I could verify the problem here (when writing both files, the content of the second writing will be written into the first file too), however I would have expected that the second file open returns a negative error code.

Thanks,
Geza

[geky]

Ah! good idea. I just didn't think of returning an error code in that condition.

Does this fix look good to you? (returns LFS_ERR_NOMEM / -ENOMEM)
https://github.com/geky/littlefs/compare/fix-multi-static-file

[kewld]

@husigeza without dynamic memory allocation , are you saying we can still use LittleFS with static buffers ? I am trying to use littleFS for my STM where I dont have dynamic memory.

[husigeza]

@kewld yes, it is possible, however there are limitations, such as you can only have 1 file opened at a time.

[FreddieChopin]

@kewld yes, it is possible, however there are limitations, such as you can only have 1 file opened at a time.

Not true.

I am trying to use littleFS for my STM where I dont have dynamic memory.

You have "dynamic memory" - just use it.

[geky]

@kewld yes, it is possible, however there are limitations, such as you can only have 1 file opened at a time.

Not true.

This changed in v1.5: https://github.com/ARMmbed/littlefs/pull/58

It was true when this issue was created :) Which means I've probably left this issue open for too long. Feel free to reopen if there's still an issue.

are you saying we can still use LittleFS with static buffers ?

You can specify a buffer per file using lfs_file_opencfg:

// must be equal to cache size in lfs config
uint8_t file_buffer[config.cache_size];
// note we must zero initialize unused fields for backwards compatibility
// designated initializers do this for us
struct lfs_file_config file_config = {
    .buffer = file_buffer;
};
// open file
lfs_file_t file;
int err = lfs_file_opencfg(&lfs, &file, "path/to/file",
        LFS_O_WRONLY | LFS_O_CREAT, &file_config);
assert(!err);

[nickray]

You have "dynamic memory" - just use it.

Not using heap allocations is a legitimate use case - not everyone splashes around with an RTOS :yum:.

I'm happy to report I just got LittleFS to run via Rust bindings on an STM32L432 microcontroller - no heap allocations, no libc. I only had to patch in some implementations.

[FreddieChopin]

Not using heap allocations is a legitimate use case - not everyone splashes around with an RTOS

Using or not using dynamic allocations have nothing to do with a RTOS.

[geky]

I'm happy to report I just got LittleFS to run via Rust bindings on an STM32L432 microcontroller

Cool! Is this with the littlefs crate I've seen floating around?
https://docs.rs/littlefs/0.2.0/littlefs/

Which means I've probably left this issue open for too long. Feel free to reopen if there's still an issue.

I wrote that then forgot to actually close this! closing... (discussion can still continue)

[nickray]

Cool! Is this with the littlefs crate I've seen floating around?
https://docs.rs/littlefs/0.2.0/littlefs/

Yeah, I bumped it to v2 and had to patch it a little, looking forward to using file attributes which should come in handy. Implementing the Storage trait felt really really nice and elegant, I'm in a honeymoon/fanboy phase with your littlefs currently!