testing/ostest: split the fork test into task_fork, vfork and fork

nuttx implements fork() and vfork() as the same function, and is gaining the
three separate primitives its issue #19540 describes:  task_fork() (shares
memory, private stack copy, both running), vfork() (shares memory, parent
suspended) and POSIX fork() (child gets its own copy).  This is the apps side
of that, and it lands first:  it works against nuttx with or without the
split, so the tests keep running across the transition rather than silently
compiling out.

ostest's "vfork" test was never testing vfork().  It has the child write a
global and the parent observe the write -- which is the defining property of
*sharing*, not of vfork(), whose defining property is that the parent is
suspended and whose contract forbids the child to write anything at all.  It
is renamed to task_fork.c, unchanged, because that is the primitive it has
always described.

vfork.c is rewritten to test what vfork() promises.  The child does only what
POSIX permits -- it calls _exit(42), and nothing else, not even exit(), which
would run atexit handlers and flush stdio in the parent's address space.  The
observable is therefore the child's exit status rather than a memory write.
Where child status is not retained -- ostest_main() sets SA_NOCLDWAIT for the
whole run, deliberately -- waitpid() returning ECHILD is accepted as equally
good evidence:  it says the child was already gone when the parent asked.

fork.c is new and tests POSIX fork():  the child's writes to .data, .bss and
the heap are invisible to the parent and vice versa, a pointer to a stack
local taken before the fork names the same object in both, and the child does
everything a vfork() child may not -- calls malloc() and printf(), and returns
from the function that called fork().

All three run at the top of user_main() rather than in the middle.  They
exercise the lowest-level machinery in the suite -- address environments,
stack setup, the architecture's register context -- so a fault in one takes
the process down instead of reporting a failure, and finding that out in
seconds rather than after everything else has passed is the difference
between a usable iteration and a coffee break when a port is being brought
up.

The other in-tree callers are audited for which primitive they actually
meant.  nand_sim wants a daemon that outlives its caller and shares its
memory, which is task_fork().  bas's SHELL and EDIT statements, python's
_posixsubprocess and libwebsockets' feature macros want the fork-then-exec
path, which vfork() serves; python's os.fork() and libwebsockets'
LWS_HAVE_FORK stay on fork() proper.  fdsantest's vfork case follows vfork().

Two third-party suites need their source lists narrowed, because they call
fork() from code that is compiled unconditionally:

* system/libuv -- test-fork.c and test-pipe-close-stdout-read-stdin.c are
  filtered out of the test-*.c glob.  Every test they define is already
  excluded from the task list on NuttX by 0001-libuv-port-for-nuttx.patch --
  the nine fork_* entries and pipe_close_stdout_read_stdin -- so they were
  dead code being compiled only because fork() happened to be declared.
* testing/ltp -- the open_posix_testsuite is filtered through the existing
  BLACKWORDS mechanism, which already drops tests for absent features and is
  already conditioned on configuration symbols.  Where fork() is not
  provided this drops 278 of 1943 test files; the pattern is written to spare
  vfork() and task_fork(), which remain available.  Where fork() is provided
  -- which today is everywhere -- nothing is dropped.

Compatibility: CONFIG_ARCH_HAVE_TASK_FORK and CONFIG_ARCH_HAVE_VFORK do not
exist in nuttx yet, so everything here also accepts the CONFIG_ARCH_HAVE_FORK
that stands in for them today -- today's fork() *is* task_fork(), and today's
vfork() is that plus a waitpid().  fork_test() deliberately has no such
fallback:  the copy semantics it checks are exactly what today's fork() does
not provide, so it is gated on ARCH_HAVE_VFORK, whose existence is the
evidence that the split has landed.  A follow-up removes the fallbacks once
it has.

Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com>

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: casaroli

interpreters/python/Makefile

@@ -114,6 +114,11 @@ ifeq ($(CONFIG_ARCH_HAVE_FORK),y)
 else
 	@echo "export ac_cv_func_fork=\"no\"" >> $@
 endif
+ifneq ($(CONFIG_ARCH_HAVE_VFORK)$(CONFIG_ARCH_HAVE_FORK),)
+	@echo "export ac_cv_func_vfork=\"yes\"" >> $@
+else
+	@echo "export ac_cv_func_vfork=\"no\"" >> $@
+endif
 ifeq ($(CONFIG_SYSTEM_SYSTEM),y)
 	@echo "export ac_cv_func_system=\"yes\"" >> $@
 else
@@ -135,7 +140,10 @@ endif
 
 $(SETUP_LOCAL):
 	$(Q) ( cp $(SETUP_LOCAL).in $(SETUP_LOCAL))
-ifneq ($(CONFIG_ARCH_HAVE_FORK),y)
+# _posixsubprocess is the fork-then-exec path, so vfork() is enough for it;
+# os.fork() itself needs a real fork() and is governed by ac_cv_func_fork
+# above.
+ifeq ($(CONFIG_ARCH_HAVE_FORK)$(CONFIG_ARCH_HAVE_VFORK),)
 	@echo "_posixsubprocess" >> $@
 endif
 ifneq ($(CONFIG_LIBC_DLFCN),y)

netutils/libwebsockets/lws_config_private.h

@@ -43,7 +43,10 @@
 /* #undef USE_CYASSL */
 
 /* Define to 1 if you have the `fork' function. */
+
+#ifdef CONFIG_ARCH_HAVE_FORK
 #define LWS_HAVE_FORK
+#endif
 
 #ifndef CONFIG_DISABLE_ENVIRON
 /* Define to 1 if you have the `getenv' function. */
@@ -111,10 +114,14 @@
 /* #undef LWS_HAVE_VFORK_H */
 
 /* Define to 1 if `fork' works. */
+#ifdef CONFIG_ARCH_HAVE_FORK
 #define LWS_HAVE_WORKING_FORK
+#endif
 
 /* Define to 1 if `vfork' works. */
+#if defined(CONFIG_ARCH_HAVE_VFORK) || defined(CONFIG_ARCH_HAVE_FORK)
 #define LWS_HAVE_WORKING_VFORK
+#endif
 
 /* Define to 1 if execvpe() exists */
 #define LWS_HAVE_EXECVPE

system/libuv/CMakeLists.txt

@@ -171,6 +171,11 @@ if(CONFIG_LIBUV)
         ${LIBUV_TEST_DIR}/run-tests.c ${LIBUV_TEST_DIR}/runner.c
         ${LIBUV_TEST_DIR}/runner-unix.c ${LIBUV_TEST_DIR}/echo-server.c)
     file(GLOB TEST_CSRCS ${LIBUV_TEST_DIR}/test-*.c)
+
+    # See system/libuv/Makefile.
+
+    list(REMOVE_ITEM TEST_CSRCS ${LIBUV_TEST_DIR}/test-fork.c
+         ${LIBUV_TEST_DIR}/test-pipe-close-stdout-read-stdin.c)
     list(APPEND LIBUV_UTILS_TEST_SRCS ${TEST_CSRCS})
     nuttx_add_application(
       NAME

system/libuv/Makefile

@@ -144,7 +144,15 @@ CSRCS += runner.c
 CSRCS += runner-unix.c
 CSRCS += echo-server.c
 
-CSRCS += $(wildcard libuv/test/test-*.c)
+# test-fork.c and test-pipe-close-stdout-read-stdin.c call fork().  Every
+# test they define is already excluded from the task list on NuttX by
+# 0001-libuv-port-for-nuttx.patch, so they are dead code here.
+
+LIBUV_TEST_CSRCS  = $(wildcard libuv/test/test-*.c)
+LIBUV_TEST_CSRCS := $(filter-out libuv/test/test-fork.c,$(LIBUV_TEST_CSRCS))
+LIBUV_TEST_CSRCS := $(filter-out libuv/test/test-pipe-close-stdout-read-stdin.c,$(LIBUV_TEST_CSRCS))
+
+CSRCS += $(LIBUV_TEST_CSRCS)
 endif
 
 ifneq ($(CONFIG_LIBUV_UTILS_BENCHMARK),)

testing/drivers/nand_sim/Kconfig

@@ -6,6 +6,7 @@
 config TESTING_NAND_SIM
 	boolean "NAND Flash Simulator"
 	depends on MTD_NAND_RAM && ENABLE_ALL_SIGNALS
+	depends on ARCH_HAVE_TASK_FORK || ARCH_HAVE_FORK
 	default n
 	---help---
 		Enable the NAND Flash Simulator device.

testing/drivers/nand_sim/nand_sim_main.c

@@ -25,7 +25,9 @@
  ****************************************************************************/
 
 #include <nuttx/debug.h>
+#include <sched.h>
 #include <stdio.h>
+#include <unistd.h>
 
 #include <nuttx/drivers/drivers.h>
 #include <nuttx/mtd/nand.h>
@@ -140,9 +142,16 @@ int main(int argc, FAR char *argv[])
   int   ret;
   pid_t pid;
 
-  /* Daemon */
+  /* task_fork() rather than fork():  this wants a clone that outlives the
+   * caller and shares its memory.  The fallback below covers a nuttx that
+   * does not have task_fork() yet.
+   */
 
-  pid = fork();
+#ifndef CONFIG_ARCH_HAVE_TASK_FORK
+#  define task_fork() fork()
+#endif
+
+  pid = task_fork();
 
   if (pid > 0)
     {

testing/fs/fdsantest/fdsantest_simple.c

@@ -96,6 +96,7 @@ static void test_case_overflow(void **state)
   assert_int_equal(open_count, close_count);
 }
 
+#if defined(CONFIG_ARCH_HAVE_VFORK) || defined(CONFIG_ARCH_HAVE_FORK)
 static void test_case_vfork(void **state)
 {
   int fd = open("/dev/null", O_RDONLY);
@@ -112,6 +113,7 @@ static void test_case_vfork(void **state)
 
   android_fdsan_close_with_tag(fd, 0xbadc0de);
 }
+#endif
 
 /****************************************************************************
  * Public Functions
@@ -129,7 +131,9 @@ int main(int argc, FAR char *argv[])
     cmocka_unit_test(test_case_unowned_tagged_close),
     cmocka_unit_test(test_case_owned_tagged_close),
     cmocka_unit_test(test_case_overflow),
+#if defined(CONFIG_ARCH_HAVE_VFORK) || defined(CONFIG_ARCH_HAVE_FORK)
     cmocka_unit_test(test_case_vfork),
+#endif
   };
 
   return cmocka_run_group_tests(tests, NULL, NULL);

testing/ltp/CMakeLists.txt

@@ -86,6 +86,12 @@ if(CONFIG_TESTING_LTP)
       list(APPEND BLACKWORDS "pthread_spin_init" "pthread_spin_destroy"
            "pthread_spin_trylock")
     endif()
+
+    # See testing/ltp/Makefile.
+
+    if(NOT CONFIG_ARCH_HAVE_FORK AND NOT CONFIG_FORK_IS_TASK_FORK)
+      list(APPEND BLACKWORDS "[^v_]fork(")
+    endif()
     list(
       APPEND
       BLACKWORDS

testing/ltp/Makefile

@@ -44,6 +44,13 @@ BLACKWORDS  += "pthread_spin_destroy"
 BLACKWORDS  += "pthread_spin_trylock"
 endif
 
+# Where NuttX does not declare fork(), a test that calls it cannot be built.
+# The pattern spares vfork() and task_fork(), which remain available.
+
+ifeq ($(CONFIG_ARCH_HAVE_FORK)$(CONFIG_FORK_IS_TASK_FORK),)
+BLACKWORDS  += "[^v_]fork("
+endif
+
 BLACKWORDS  += "CHILD_MAX"
 BLACKWORDS  += "setpgid("
 BLACKWORDS  += "PTHREAD_SCOPE_PROCESS"

testing/ostest/CMakeLists.txt

@@ -143,10 +143,19 @@ if(CONFIG_TESTING_OSTEST)
     endif()
   endif()
 
-  if(CONFIG_ARCH_HAVE_FORK)
-    if(CONFIG_SCHED_WAITPID)
-      list(APPEND SRCS vfork.c)
-    endif()
+  # See testing/ostest/Makefile for why each test also accepts the symbol that
+  # stands in for it on a nuttx without the fork()/vfork() split.
+
+  if(CONFIG_ARCH_HAVE_TASK_FORK OR CONFIG_ARCH_HAVE_FORK)
+    list(APPEND SRCS task_fork.c)
+  endif()
+
+  if(CONFIG_ARCH_HAVE_VFORK OR (CONFIG_ARCH_HAVE_FORK AND CONFIG_SCHED_WAITPID))
+    list(APPEND SRCS vfork.c)
+  endif()
+
+  if(CONFIG_ARCH_HAVE_FORK AND CONFIG_ARCH_HAVE_VFORK)
+    list(APPEND SRCS fork.c)
   endif()
 
   if(CONFIG_ARCH_SETJMP_H)