Add atomvm:subprocess/4 performing pipe/fork/execve`

This is implemented using pipe/fork/execve or posix_spawn depending on
platforms and availability of `HAVE_POSIX_SPAWN_CLOEXEC_DEFAULT` attribute.
The VM does not leak any file descriptor to the subprocess except for the
pipe used to read stdout.

The function is explicitely disabled on microcontrollers and is meant to be
used on generic_unix platform, for example for tests.

Signed-off-by: Paul Guyot <[email protected]>

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added support for external refs and encoded refs in external terms
 - Introduce ports to represent native processes and added support for external ports and encoded ports in external terms
 - Added `atomvm:get_creation/0`, equivalent to `erts_internal:get_creation/0`
+- Added `atomvm:subprocess/4` to perform pipe/fork/execve on POSIX platforms
 
 ### Fixed
 

libs/eavmlib/src/atomvm.erl

@@ -44,7 +44,8 @@
     posix_opendir/1,
     posix_closedir/1,
     posix_readdir/1,
-    get_creation/0
+    get_creation/0,
+    subprocess/4
 ]).
 
 -export_type([
@@ -341,3 +342,19 @@ posix_readdir(_Dir) ->
 -spec get_creation() -> non_neg_integer().
 get_creation() ->
     erlang:nif_error(undefined).
+
+%%-----------------------------------------------------------------------------
+%% @param   Path    path to the command to execute
+%% @param   Args    arguments to pass to the command. First item is the name
+%%                  of the command
+%% @param   Envp    environment variables to pass to the command.
+%% @param   Options options to run execve. Should be `[stdout]'
+%% @returns a tuple with the process id and a fd to the stdout of the process.
+%% @doc     Fork and execute a program using fork(2) and execve(2). Pipe stdout
+%%          so output of the program can be read with `atomvm:posix_read/2'.
+%% @end
+%%-----------------------------------------------------------------------------
+-spec subprocess(Path :: iodata(), Args :: [iodata()], Env :: [iodata()], Options :: [stdout]) ->
+    {ok, non_neg_integer(), posix_fd()} | {error, posix_error()}.
+subprocess(_Path, _Args, _Env, _Options) ->
+    erlang:nif_error(undefined).

src/libAtomVM/CMakeLists.txt

@@ -199,6 +199,9 @@ define_if_function_exists(libAtomVM closedir "dirent.h" PUBLIC HAVE_CLOSEDIR)
 define_if_function_exists(libAtomVM mkfifo "sys/stat.h" PRIVATE HAVE_MKFIFO)
 define_if_function_exists(libAtomVM readdir "dirent.h" PUBLIC HAVE_READDIR)
 define_if_function_exists(libAtomVM unlink "unistd.h" PRIVATE HAVE_UNLINK)
+define_if_function_exists(libAtomVM execve "unistd.h" PRIVATE HAVE_EXECVE)
+define_if_function_exists(libAtomVM closefrom "unistd.h" PRIVATE HAVE_CLOSEFROM)
+define_if_symbol_exists(libAtomVM POSIX_SPAWN_CLOEXEC_DEFAULT "spawn.h" PRIVATE HAVE_POSIX_SPAWN_CLOEXEC_DEFAULT)
 define_if_symbol_exists(libAtomVM O_CLOEXEC "fcntl.h" PRIVATE HAVE_O_CLOEXEC)
 define_if_symbol_exists(libAtomVM O_DIRECTORY "fcntl.h" PRIVATE HAVE_O_DIRECTORY)
 define_if_symbol_exists(libAtomVM O_DSYNC "fcntl.h" PRIVATE HAVE_O_DSYNC)

src/libAtomVM/nifs.c

@@ -851,8 +851,14 @@ DEFINE_MATH_NIF(tanh)
 //Handle optional nifs
 #if HAVE_OPEN && HAVE_CLOSE
 #define IF_HAVE_OPEN_CLOSE(expr) (expr)
+#if HAVE_EXECVE
+#define IF_HAVE_EXECVE(expr) (expr)
+#else
+#define IF_HAVE_EXECVE(expr) NULL
+#endif
 #else
 #define IF_HAVE_OPEN_CLOSE(expr) NULL
+#define IF_HAVE_EXECVE(expr) NULL
 #endif
 #if HAVE_MKFIFO
 #define IF_HAVE_MKFIFO(expr) (expr)

src/libAtomVM/nifs.gperf

@@ -148,6 +148,7 @@ atomvm:posix_write/2, IF_HAVE_OPEN_CLOSE(&atomvm_posix_write_nif)
 atomvm:posix_select_read/3, IF_HAVE_OPEN_CLOSE(&atomvm_posix_select_read_nif)
 atomvm:posix_select_write/3, IF_HAVE_OPEN_CLOSE(&atomvm_posix_select_write_nif)
 atomvm:posix_select_stop/1, IF_HAVE_OPEN_CLOSE(&atomvm_posix_select_stop_nif)
+atomvm:subprocess/4, IF_HAVE_EXECVE(&atomvm_subprocess_nif)
 atomvm:posix_mkfifo/2, IF_HAVE_MKFIFO(&atomvm_posix_mkfifo_nif)
 atomvm:posix_unlink/1, IF_HAVE_UNLINK(&atomvm_posix_unlink_nif)
 atomvm:posix_clock_settime/2, IF_HAVE_CLOCK_SETTIME_OR_SETTIMEOFDAY(&atomvm_posix_clock_settime_nif)