Translate fcntl flock l_type between Linux and macOS

[Max042004]

Problem

The F_GETLK/F_SETLK/F_SETLKW handler in src/syscall/fs.c copied the
guest's l_type field straight into the host struct flock, on the
assumption (stated in a comment) that the lock-type constants match. They do
not:

constant	Linux aarch64	macOS / BSD
F_RDLCK	0	1
F_WRLCK	1	3
F_UNLCK	2	2

A Linux F_RDLCK (0) is not a valid lock type on macOS, so the host
fcntl() rejects it with EINVAL. POSIX-locking databases take a shared
read lock first, so this breaks them. Concretely, SQLite fails to open any
on-disk database with disk I/O error (10): its initial F_RDLCK on the
1 GiB "pending byte" never succeeds. In-memory databases are unaffected,
which is what made this easy to miss.

Trace from a failing sqlite3 file.db "CREATE TABLE ..." under --verbose:

syscall 25@... (0x3, 0x6, 0x7ffc490, ...)   # fcntl(fd=3, F_SETLK=6, &flock)
  -> -22 (EINVAL)

Fix

Map l_type Linux→macOS on input for all three commands, and map it back
macOS→Linux when writing the F_GETLK result. Unknown types are rejected
with EINVAL rather than passed through.

Test

Adds tests/test-flock.c (registered in manifest.txt under "Syscall
coverage tests"), which exercises F_SETLK/F_SETLKW/F_GETLK around the
same 1 GiB pending-byte offsets SQLite uses. It fails with errno 22
before this change and passes after — verified by reverting the fix.

Validation

• make check: all 97 tests pass (including the new test-flock).
• Local CI replication: check-newline, check-format (clang-format 22),
  check-security, cppcheck, syscall-dispatch consistency, and
  make lint all clean; make elfuse builds and codesigns.
• End-to-end with a statically cross-compiled aarch64 SQLite 3.47.2: on-disk
  CRUD, transactions, JSON1 function indexes, FTS5, WAL + wal_checkpoint,
  a 50k-row transaction, and .dump/.read round-trips all succeed; the
  resulting file is readable by the host sqlite3.

---

Summary by cubic

Fixes fcntl lock-type translation between Linux guests and macOS hosts to prevent EINVAL on valid read locks. Restores on-disk SQLite and other POSIX-locking apps by correctly mapping l_type for F_GETLK, F_SETLK, and F_SETLKW.

• Bug Fixes
  • Map l_type Linux→macOS on input and macOS→Linux on F_GETLK output; reject unknown types with EINVAL.
  • Add tests/test-flock.c (registered in tests/manifest.txt) to cover SQLite’s pending-byte lock pattern; failed before, passes now.

^{Written for commit 63e7a93. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}

[jserv]

Thank @Max042004 for contributing!