Changelog

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog, and this project adheres to Semantic Versioning.

[1.1.2] - 2026-05-10

SIGBUS handler no longer reads __thread storage on the signal path. iommap_nif.so is loaded via dlopen, so on FreeBSD (and any other platform whose dynamic loader allocates dlopened TLS lazily) reading a __thread variable from a thread that has not yet executed iommap code can call __tls_get_addr, which in turn may call malloc -- not async-signal-safe, leading to a crash on the next bus error. The protection state is now carried in a pthread_key_t slot allocated eagerly by iommap NIF entry points; the handler does a plain pthread_getspecific and treats a NULL slot as "not in a protected region, chain to the previous handler". This is the second half of the SIGBUS-handler fix started in 1.1.1; the crash only showed up when iommap was paired with another NIF in the same BEAM (enough TLS pressure to push iommap's slot out of the static-TLS reserve).

New iommap_two_nif_tests module reproduces the FreeBSD segfault inside iommap. A test-only helper NIF (test/c_src/) registers its own resource types alongside iommap; the test runs the region_binary load pattern in a tight loop, both inline and from a dedicated worker process. Without the TLS fix this reliably crashed BEAM on FreeBSD 14.2 and 14.4 in CI; with the fix, all matrix entries pass.

SIGBUS handler chains to the previously-installed handler when fired outside any iommap-protected region. The earlier handler always longjmped through a thread-local sigjmp_buf even when no sigsetjmp had run, which caused process segfaults when iommap was loaded alongside other NIFs that perform mmap I/O.
IOMMAP_MODE_WRITE now opens the file O_RDWR. mmap with PROT_WRITE requires a readable fd; the previous O_WRONLY broke write-only mode at mmap time.
pread/3 and region_binary/3 reject write-only handles with eacces, matching the symmetric guard already in pwrite/3.
pwrite/3 now wraps its memcpy in the same enter/leave protected pair as pread/3 so a SIGBUS during pwrite is reported as {error, sigbus} rather than chained to the default handler.

New read_close_then_parse and many_open_close_cycles cases cover the read-only open → region_binary → close → use binary pattern that downstream callers rely on.
FreeBSD CI now matrices 14.2 and 14.4.

iommap:region_binary/3 returns a refcounted resource binary that points directly into the mapped region, with no data copy. Intended for hot zero-copy hand-off paths.

The NIF resource layout was split into a mapping resource (owns the mmap region and fd) and a handle resource (owns the BEAM handle term and one reference to the mapping). close/1 releases the handle's reference to the mapping; munmap and close(fd) are deferred until any outstanding region binaries derived from that mapping are also garbage collected. Existing API behaviour is unchanged.
truncate/2 now allocates a fresh mapping (with a duplicated fd) and atomically swaps it into the handle. The previous mapping remains alive for outstanding region binaries.

region_binary/3 is unsafe against external truncation that shrinks past a binary's range. Use pread/3 when safety against external mutation is required.

Initial release of iommap
Dirty NIF I/O schedulers for all I/O operations
Cross-platform memory-mapped file I/O for Erlang/OTP
Support for Linux, macOS, FreeBSD, and OpenBSD
Core operations: open/2,3, close/1, pread/3, pwrite/3
Synchronization: sync/1,2 with sync/async modes
File management: truncate/2, position/1
Memory advice: advise/4 with madvise hints
Thread-safe implementation using pthread rwlocks
SIGBUS protection for external file truncation
Platform-specific optimizations:
- MAP_POPULATE support on Linux
- MAP_NOCACHE support on macOS
- fallocate on Linux, posix_fallocate on BSD
Comprehensive test suite with 20 tests
CI pipeline for all supported platforms