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D-Modem on Haiku: technical details

This is the technical companion to D-Modem on Haiku, the plain-English overview. Start there; this page keeps the full detail: the code's names, the Recommendations' clauses, the numbers and the test lists.

dmodemd builds for Haiku, the open successor to BeOS: R1/beta5 and later, on x86_64.

It is the same modem as on Linux: - SIP (internet telephony) through the libre library; - the open DSP: data up to V.34, V.90/V.92 as the digital modem, class 1 fax and voice; - T.38 fax over IP; - a pty (pseudo-terminal) as its DTE, the serial device that programs talk AT commands to.

The USB modems (--usb) are built in too: Smart Link's SmartUSB56, the pico-serial Line and WB sticks, and Agere's USB 2.0 soft modem. dmodemd reaches them through HaikuPorts' libusb.

These also build for Haiku: - libdmodem (frontend/dmodemd/dmodem.h); - libdmodem_sip.a; - dmodem-ari; - the test programs.

These are not built for Haiku: - The ALSA line (-a), --misdn and hda-modem-setup: they are Linux's own. - The Asterisk and FreeSWITCH modules: neither PBX has been ported to Haiku.

Status

The build is checked from Linux: CI's haiku job (.github/workflows/ci.yml) cross-builds it with Clang, with warnings as errors, and keeps dmodemd as an artifact (dmodemd-haiku-x86_64).

Nothing has run on Haiku itself yet: neither the tests nor a call.

Building on Haiku

Haiku already has GCC and its headers (haiku_devel). The rest comes from HaikuPorts:

pkgman install cmake ninja git pkgconfig libusb_devel
cmake -B build -G Ninja
cmake --build build
ctest --test-dir build -L quick

libre (the SIP library) and Mbed TLS (its crypto) are fetched and built while configuring, libre with a small patch for Haiku (platforms/haiku/libre-haiku.patch). Without libusb_devel, dmodemd builds without --usb.

cmake --install build puts the programs in /boot/system/non-packaged/bin, which is on the PATH. /boot/system itself belongs to Haiku's packages and is read-only.

Building on Linux

Clang and lld (version 17 or later) can build for Haiku against a sysroot made of Haiku's own packages. platforms/haiku/haiku_sysroot.py makes one: 1. It downloads the packages from Haiku's and HaikuPorts' repositories, once, into a cache (by default haiku-packages beside the sysroot). 2. It checks each package against its repository's SHA-256. 3. It extracts each one under boot/system, as Haiku installs it.

The script reads Haiku's package format itself. Its zstd-compressed packages need the system's libzstd.

sudo apt-get install cmake ninja-build pkg-config clang lld libzstd1
python3 platforms/haiku/haiku_sysroot.py ~/haiku-sysroot
cmake -B build-haiku -G Ninja -DCMAKE_TOOLCHAIN_FILE=platforms/haiku/haiku.cmake \
      -DHAIKU_SYSROOT=$HOME/haiku-sysroot
cmake --build build-haiku

The sysroot is about 500 MB. It holds: - the base system: haiku, haiku_devel; - GCC's headers and libraries: gcc, gcc_syslibs, gcc_syslibs_devel (Clang uses GCC's libstdc++); - libusb and libusb_devel.

The tests are built but not registered with ctest, because nothing on Linux can run Haiku's programs (cmake/test_logs.cmake). Copy the build to Haiku to run them.

Running

dmodemd takes the same options as on Linux (see Using dmodemd). The differences are these.

No users. Every process on Haiku has uid 0, and there is no other user to run as. So dmodemd does not give up root's rights after start-up (started_as_root() in frontend/dmodemd/main.cpp is always false there), and it forks no keeper process for the pty's link.

The pty. The pty is one of Haiku's (/dev/pt/<n>, with its slave at /dev/tt/<n>). - dmodemd also tries to make the link /dev/ttyDM<n> to it. - If Haiku's /dev refuses the link, use the path that dmodemd prints at start-up (Use `...' as modem device).

Real-time scheduling. Haiku has no mlockall() and no SCHED_FIFO. - Without -n, the line's thread gets a real-time priority (B_REAL_TIME_DISPLAY_PRIORITY). Such a thread runs until it blocks, as a SCHED_FIFO one does. - Threads made later, such as the SIP user agent's, keep the normal priority.

The data file. The modem keeps its data file in /var/lib/dmodem/data.<name> (on Haiku /var is /boot/system/var). Make the directory first:

mkdir -p /var/lib/dmodem

USB. libusb drives a USB modem through Haiku's usb_raw driver. - All four modems stream their samples over isochronous endpoints: the SmartUSB56, the pico-serial Line and WB (the same transfers as the SmartUSB56's) and the Agere modem. - None has been tried on Haiku yet.

What the port changed

Most of the tree was POSIX already and builds unchanged. For Haiku:

  • Executables are shared objects. Haiku's linkers make every executable a shared object (-shared). So CMake's -fPIE for position-independent executables becomes -fPIC (cmake/rules.cmake, which libre's build uses too).
  • The sockets are libnetwork's, not the C library's, so every program links -lnetwork.
  • No SOCK_CLOEXEC, MSG_CMSG_CLOEXEC or ptsname_r(). Descriptors are made close-on-exec with fcntl(), and a pty's slave is named with ptsname(). frontend/dmodemd/portable.h already did the first on Apple's systems.
  • No <sys/syscall.h>, so descriptors are closed one by one, without close_range() (frontend/dmodemd/pty.cpp).
  • libre (platforms/haiku/libre-haiku.patch):
  • Haiku's interface ioctls are in <sys/sockio.h>;
  • its struct ifreq has no ifr_ifru;
  • it has no way to list the routing table, so libre's own stub is used, as on iOS.
  • The install layout: the prefix /boot/system/non-packaged, data/ in place of share/, and bin/ in place of sbin/.