Fix compile errors if c_int is not i32 on some platforms

[bytedream]

The error type of littlefs is c_int. On most platforms this equals to i32 and the littlefs2 crate also asserts that, but there are some platforms (like AVR) where c_int is i16 and compiling will result in an error. This PR adds support for those platforms where c_int is i16.

Example build instructions for Atmega328p

Prerequisites (for debian; can be directly used in the rust docker image; workdir must be the root of the littlefs2 crate):

# install avr compiler
apt update
apt install -y gcc-avr avr-libc clang

# the nightly compiler is required
rustup toolchain install --profile minimal --component=rust-src nightly

# target configuration for the atmega328p chip. there also is a avr-unknown-gnu-atmega328 target, but manually defining a file is much more easy than using it
cat <<EOT > avr-atmega328p.json
{
  "arch": "avr",
  "atomic-cas": false,
  "cpu": "atmega328p",
  "data-layout": "e-P1-p:16:8-i8:8-i16:8-i32:8-i64:8-f32:8-f64:8-n8-a:8",
  "eh-frame-header": false,
  "exe-suffix": ".elf",
  "late-link-args": {
    "gcc": [
      "-lgcc"
    ]
  },
  "linker": "avr-gcc",
  "llvm-target": "avr-unknown-unknown",
  "max-atomic-width": 8,
  "no-default-libraries": false,
  "pre-link-args": {
    "gcc": [
      "-mmcu=atmega328p"
    ]
  },
  "relocation-model": "static",
  "target-c-int-width": "16",
  "target-pointer-width": "16"
}
EOT

# apply patch described in https://github.com/trussed-dev/littlefs2/issues/30#issuecomment-1472190645
echo 'delog = { version = "0.1.6", git = "https://github.com/LechevSpace/delog.git", rev = "e83f3fd" }' >> Cargo.toml
cargo update

Compile:

cargo +nightly build -Z build-std=core --target=./avr-atmega328p.json --release

[robin-nitrokey]

Thanks for the PR! We’ve refactored the error type in #67 and I think I already fixed some of the problems as part of it. I’ll have another look at the remaining changes.

[robin-nitrokey]

@bytedream Please review #69 and check if it fixes your build.

[bytedream]

@robin-nitrokey yes this fixes it, thank you