Make non-glibc Linux cross-compilation work

[Schnitzel]

Summary

Three small changes that let mujina-miner cross-compile for aarch64-unknown-linux-musl (and other non-glibc Linux targets), so it can be deployed onto mining hardware that ships with musl userspace — concretely, the Amlogic A113D control board found on Antminer S19 series miners.

• Switch reqwest to rustls-tls. The default features pull in native-tls, which transitively requires openssl-sys. Cross-building openssl-sys to musl is painful (sysroot, pkg-config wrapper, vendored OpenSSL or a sysroot install) and unnecessary when reqwest can use rustls directly.
• Gate udev and tracing-journald to target_env = "gnu". Both link against glibc-only system libraries (libudev, libsystemd) that have no good musl story. The existing fallback mod platform in src/transport/usb.rs already covers the no-udev case as a stub for unsupported platforms (Windows, etc.), so musl Linux now falls into that same path — fine for the CPU backend and any non-USB hashboard.
• Same cfg change in src/tracing.rs so the journald init mod follows the same gate as its dependency.

Net diff: 4 files, +7 / -7 lines.

Test plan

• cargo build --release on macOS (aarch64-apple-darwin) — unchanged, still builds.
• cargo build --release --target aarch64-unknown-linux-musl --bin mujina-minerd from macOS — now succeeds (previously failed at openssl-sys and udev).
• Resulting 17 MB statically-linked aarch64 ELF transferred to an Antminer S19j Pro control board (LuxOS base, kernel aarch64 / userspace armhf — the static aarch64 binary runs fine via the 64-bit kernel).
• MUJINA_CPUMINER_THREADS=1 MUJINA_CPUMINER_DUTY=50 MUJINA_USB_DISABLE=1 MUJINA_API_LISTEN=0.0.0.0:7785 ./mujina-minerd — comes up cleanly, CPU board attached, dummy job source, REST API responds at /swagger-ui, mining-status log line ticks at 30s.

Build steps on macOS

rustup target add aarch64-unknown-linux-musl
brew install messense/macos-cross-toolchains/aarch64-unknown-linux-musl

CARGO_TARGET_AARCH64_UNKNOWN_LINUX_MUSL_LINKER=aarch64-unknown-linux-musl-gcc \
CC_aarch64_unknown_linux_musl=aarch64-unknown-linux-musl-gcc \
  cargo build --release --target aarch64-unknown-linux-musl --bin mujina-minerd

Notes / open questions

• The reqwest rustls swap is mildly opinionated. If you'd prefer to keep native-tls as the default and offer rustls behind a feature flag instead, happy to refactor — but it'd add complexity for the cross-build path with no obvious upstream benefit.
• This is the minimal change to make the build work. Real S19 hashboard support (driving BM1362 chips over UART, APW12 PSU over I²C, fans, EEPROM decode, PIC sensor reads) is separate work — see skot/amlogic-cb-tools for the standalone hardware-validation binaries that prove out the control-board interfaces before they land in mujina.

[Copilot]

Pull request overview

This PR adjusts mujina-miner to successfully cross-compile for non-glibc Linux targets (notably aarch64-unknown-linux-musl) by avoiding glibc-only system integrations and removing OpenSSL/native-tls requirements from the HTTP client dependency chain.

Changes:

• Switch workspace reqwest configuration to default-features = false and enable rustls-tls (avoids openssl-sys).
• Gate Linux-only dependencies (udev, tracing-journald) to cfg(all(target_os = "linux", target_env = "gnu")).
• Gate Linux journald initialization and Linux USB serial-port discovery code to the same glibc-only cfg, falling back to stub behavior on musl.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
Cargo.toml	Reconfigures reqwest to use rustls and avoid native-tls/OpenSSL.
mujina-miner/Cargo.toml	Limits udev and tracing-journald dependencies to glibc Linux targets.
mujina-miner/src/transport/usb.rs	Limits Linux USB serial-port discovery module to glibc Linux; uses stub elsewhere (incl. musl).
mujina-miner/src/tracing.rs	Limits journald init module to glibc Linux; uses stub elsewhere.

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