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1	$Id: Fork.os2 1281 2004-03-06 21:48:26Z bird $
2
3	Fork Design Draft
4	--------------------
5
6	1.0 Intro
7	----------
8
9	blah.
10
11
12	1.1 The SuS fork() Description
13	------------------------------
14
15	NAME
16
17	fork - create a new process
18
19	SYNOPSIS
20
21	#include <unistd.h>
22
23	pid_t fork(void);
24
25	DESCRIPTION
26
27	The fork() function shall create a new process. The new process (child process) shall be an exact copy of the calling process (parent process) except as detailed below:
28
29	* The child process shall have a unique process ID.
30	* The child process ID also shall not match any active process
31	group ID.
32	* The child process shall have a different parent process ID,
33	which shall be the process ID of the calling process.
34	* The child process shall have its own copy of the parent's file
35	descriptors. Each of the child's file descriptors shall refer
36	to the same open file description with the corresponding file
37	descriptor of the parent.
38	* The child process shall have its own copy of the parent's open
39	directory streams. Each open directory stream in the child process
40	may share directory stream positioning with the corresponding
41	directory stream of the parent.
42	* [XSI] The child process shall have its own copy of the parent's
43	message catalog descriptors.
44	* The child process' values of tms_utime, tms_stime, tms_cutime, and
45	tms_cstime shall be set to 0.
46	* The time left until an alarm clock signal shall be reset to zero,
47	and the alarm, if any, shall be canceled; see alarm() .
48	* [XSI] All semadj values shall be cleared.
49	* File locks set by the parent process shall not be inherited by
50	the child process.
51	* The set of signals pending for the child process shall be
52	initialized to the empty set.
53	* [XSI] Interval timers shall be reset in the child process.
54	* [SEM] Any semaphores that are open in the parent process shall
55	also be open in the child process.
56	* [ML] The child process shall not inherit any address space memory
57	locks established by the parent process via calls to mlockall()
58	or mlock().
59	* [MF\|SHM] Memory mappings created in the parent shall be retained
60	in the child process. MAP_PRIVATE mappings inherited from the
61	parent shall also be MAP_PRIVATE mappings in the child, and any
62	modifications to the data in these mappings made by the parent
63	prior to calling fork() shall be visible to the child. Any
64	modifications to the data in MAP_PRIVATE mappings made by the
65	parent after fork() returns shall be visible only to the parent.
66	Modifications to the data in MAP_PRIVATE mappings made by the
67	child shall be visible only to the child.
68	* [PS] For the SCHED_FIFO and SCHED_RR scheduling policies, the
69	child process shall inherit the policy and priority settings
70	of the parent process during a fork() function. For other s
71	cheduling policies, the policy and priority settings on fork()
72	are implementation-defined.
73	* [TMR] Per-process timers created by the parent shall not be
74	inherited by the child process.
75	* [MSG] The child process shall have its own copy of the message
76	queue descriptors of the parent. Each of the message descriptors
77	of the child shall refer to the same open message queue
78	description as the corresponding message descriptor of the parent.
79	* [AIO] No asynchronous input or asynchronous output operations
80	shall be inherited by the child process.
81	* A process shall be created with a single thread. If a
82	multi-threaded process calls fork(), the new process shall contain
83	a replica of the calling thread and its entire address space,
84	possibly including the states of mutexes and other resources.
85	Consequently, to avoid errors, the child process may only execute
86	async-signal-safe operations until such time as one of the exec
87	functions is called. [THR] Fork handlers may be established by
88	means of the pthread_atfork() function in order to maintain
89	application invariants across fork() calls.
90
91	When the application calls fork() from a signal handler and any of
92	the fork handlers registered by pthread_atfork() calls a function
93	that is not asynch-signal-safe, the behavior is undefined.
94	* [TRC TRI] If the Trace option and the Trace Inherit option are
95	both supported:
96	If the calling process was being traced in a trace stream that
97	had its inheritance policy set to POSIX_TRACE_INHERITED, the
98	child process shall be traced into that trace stream, and the
99	child process shall inherit the parent's mapping of trace event
100	names to trace event type identifiers. If the trace stream in
101	which the calling process was being traced had its inheritance
102	policy set to POSIX_TRACE_CLOSE_FOR_CHILD, the child process
103	shall not be traced into that trace stream. The inheritance
104	policy is set by a call to the posix_trace_attr_setinherited()
105	function.
106	* [TRC] If the Trace option is supported, but the Trace Inherit
107	option is not supported:
108	The child process shall not be traced into any of the trace
109	streams of its parent process.
110	* [TRC] If the Trace option is supported, the child process of
111	a trace controller process shall not control the trace streams
112	controlled by its parent process.
113	* [CPT] The initial value of the CPU-time clock of the child
114	process shall be set to zero.
115	* [TCT] The initial value of the CPU-time clock of the single
116	thread of the child process shall be set to zero.
117
118	All other process characteristics defined by IEEE Std 1003.1-2001 shall
119	be the same in the parent and child processes. The inheritance of
120	process characteristics not defined by IEEE Std 1003.1-2001 is
121	unspecified by IEEE Std 1003.1-2001.
122
123	After fork(), both the parent and the child processes shall be capable
124	of executing independently before either one terminates.
125
126	RETURN VALUE
127
128	Upon successful completion, fork() shall return 0 to the child process
129	and shall return the process ID of the child process to the parent
130	process. Both processes shall continue to execute from the fork()
131	function. Otherwise, -1 shall be returned to the parent process, no
132	child process shall be created, and errno shall be set to indicate
133	the error.
134
135	ERRORS
136
137	The fork() function shall fail if:
138
139	[EAGAIN]
140	The system lacked the necessary resources to create another
141	process, or the system-imposed limit on the total number of
142	processes under execution system-wide or by a single user
143	{CHILD_MAX} would be exceeded.
144
145	The fork() function may fail if:
146
147	[ENOMEM]
148	Insufficient storage space is available.
149
150
151
152
153	2.0 Requirements and Assumptions Of The Implementation
154	------------------------------------------------------
155
156	The Innotek LIBC fork() implementation will require the following features
157	in LIBC to work:
158	1. A shared process management internal to LIBC for communication to the
159	child that a fork() is in progress.
160	2. A very generalized and varied set of fork helper functions to archive
161	maximum flexibility of the implementation.
162	3. Extended versions of some memory related OS/2 APIs must be implemented.
163
164	The implementation will further make the following assumption about the
165	operation of OS/2:
166	1. DosExecPgm will not return till all DLLs are initated successfully.
167	2. DosQueryMemState() is broken if more than one page is specified.
168	(no idea why/how/where it's broken, but testcase shows it is :/ )
169
170
171	3.0 The Shared Process Management
172	---------------------------------
173
174	The fork() implementation requires a method for telling the child process
175	that it's being forked and must take a very different startup route. For
176	some other LIBC apis there are need for parent -> child and child -> parent
177	information exchange. More specifically, the inheritance of sockets,
178	signals, the different scheduler actions of a posix_spawn[p]() call, and
179	possibly some process group stuff related to posix_spawn too if we get it
180	figured out eventually. All this was parent -> child during spawn/fork. A
181	need also exist for child -> parent notification and possibly exchange for
182	process termination. It might be necessary to reimplement the different
183	wait apis and implement SIGCHLD, it's likely that those tasks will make
184	such demands.
185
186	The choice is now whether or not to make this shared process management
187	specific to each LIBC version as a shared segement or try to make it
188	survive normal LIBC updates. Making is specific have advantages in code
189	size and memory footprint (no reserved fields), however it have certain
190	disadvantages when LIBC is updated. The other option is to use a named
191	shared memory object, defining the content with reserved space for later
192	extensions so several versions of LIBC with more or less features
193	implemented can co use the memory space.
194
195	The latter option is prefered since it allows more applications to
196	interoperate, it causes less shared memory waste, the shared memory
197	can be located in high memory and it would be possible to fork
198	processes using multiple versions of LIBC.
199
200	The shared memory shall be named \SHAREMEM\INNOTEKLIBC.V01, the version
201	number being the one of the shared memory layout and contents, it will
202	only be increased when incompatible changes are made.
203
204	The shared memory shall be protected by an standard OS/2 mutex semaphore.
205	It shall not use any fast R3 semaphore since the the usage frequency is
206	low and the result of a messup may be disastrous. Care must be take for
207	avoiding creation races and owner died scenarios.
208
209	The memory shall have a fixed size, since adding segments is very hard.
210	Thus the size must be large enough to cope with a great deal of
211	processes, while bearing in mind that OS/2 normally doesn't support more
212	than a 1000 processes, with a theoritical max of some 4000 (being the
213	max thread count). A very simplistic allocation scheme will be
214	implemented. Practically speaking a fixed block size pool would do fine
215	for the process structure, while for the misc structures like socket
216	lists a linked list based heap would do fine.
217
218	The process blocks shall be rounded up to in size adding a reasonable
219	amount of space resevered for future extensions. Reserved space must be
220	all zeroed.
221
222	The fork() specific members of the process block shall be a pointer to
223	the shared memory object for the fork operation (the fork handle) and
224	list of forkable modules. The fork handle will it self contain
225	information indicating whether or not another LIBC version have already
226	started fork() handling in the child. The presense of the fork handle
227	means that the child is being forked and normal dll init and startup
228	will not be executed, but a registered callback will be called to do
229	the forking of each module. (more details in section 4.0)
230
231	The parent shall before spawn, fork and exec (essentially before DosExecPgm
232	or DosStartSession) create a process block for the child to be born and
233	link it into an embryo list in the shared memory block. The child shall
234	find it's process block by searching the embryo list using the parent pid
235	as key. All DosExecPgm and DosStartSession calls shall be serialized within
236	one LIBC version. (If some empty headed programmer manages to link together
237	a program which may end up using two or more LIBC versions and having two
238	or more thread doing DosExecPgm at the very same time, well then he really
239	deserves what ever trouble he gets! At least don't blame me!)
240
241	Process blocks shall have to stay around after the process terminated
242	(for child -> parent term exchange), a cleanup mechanism will be invoked
243	whenever a free memory threshold is reached. All processes will register
244	exit list handlers to mark the process block as zombie (and later
245	perhaps setting error codes and notifying waiters/child-listeners).
246
247
248
249	4.0 The fork() Implementation
250	-----------------------------
251
252
253	The implementation is based on a fork handle and a set of primitives.
254	The fork handle is a pointer to an shared memory object allocated for the
255	occation and which will be freed before fork() returns. The primitives
256	all operates on this handle and will be provided using a callback table
257	in order to fully support multiple LIBC versions.
258
259
260	4.1 Forkable Executable and DLLs
261	--------------------------------
262
263	The support for fork() is an optional feature of LIBC. The default
264	executable produced with LIBC and GCC is not be forkable. The fork
265	support will be based on registration of the DLLs and EXEs in their
266	LIBC supplied startup code (crt0/dll0). A set of fork versions of these
267	modules exist with the suffix 'fork.o'.
268
269	The big differnece between the ordinary crt0/dll0 and the forkable
270	crt0/dll0 is a per module structure, a call to register this, and the
271	handling of the return code of that call.
272
273	The fork module structure:
274	typedef struct __libc_ForkModule
275	{
276	/** Structure version. (Initially 'FMO1' as viewed in hex editor.) */
277	unsigned int iMagic;
278	/** Fork callback function */
279	int (pfnAtFork)(__LIBC_FORKMODULE pModule,
280	__LIBC_FORKHANDLE *pForkHandle, enum __LIBC_CALLBACKOPERATION enmOperation);
281	/** Pointer to the _CRT_FORK_PARENT1 set vector.
282	* It's formatted as {priority,callback}. */
283	void *pvParentVector1;
284	/** Pointer to the _CRT_FORK_CHILD1 set vector.
285	* It's formatted as {priority,callback}. */
286	void *pvChildVector1;
287	/** Data segment base address. */
288	void *pvDataSegBase;
289	/** Data segment end address (exclusive). */
290	void *pvDataSegEnd;
291	/** Reserved - must be zero. */
292	int iReserved1;
293	} __LIBC_FORKMODULE, __LIBC_PFORKMODULE; / urg! conventions */
294
295
296	The fork callback function which crt0/dll0 references when initializing
297	the fork modules structure is called _atfork_callback. It takes the fork
298	handle, module structure, and an operation enum as arguments. LIBC will
299	contain a default implementation of _atfork_callback() which simply
300	duplicates the data segment, and processes the two set vectors
301	(_CRT_FORK_*1).
302
303	crt0/dll0 will register the fork module structure and detect a forked
304	child by calling __libc_ForkRegisterModule().
305
306	Prototypes:
307	/**
308	* Register a forkable module. Called by crt0 and dll0.
309	*
310	* The call links pModule into the list of forkable modules
311	* which is maintained in the process block.
312	*
313	* @returns 0 on normal process startup.
314	* @returns 1 on forked child process startup.
315	* The caller should respond by not calling any _DLL_InitTerm
316	* or similar constructs.
317	* @returns negative on failure.
318	* The caller should return from the dll init returning FALSE
319	* or DosExit in case of crt0. _atfork_callback() will take
320	* care of necessary module initiation.
321	* @param pModule Pointer to the fork module structure for the
322	* module which is to registered.
323	*/
324	int __libc_ForkRegisterModule(__LIBC_FORKMODULE *pModule);
325
326
327
328
329
330	4.2 Fork Primitives
331	-------------------
332
333	These primitives are provided by the fork implementation in the fork
334	handle structure. We define a set of these primitives now, if later
335	new ones are added the users of these must check that they are
336	actually present.
337
338	Example:
339	rc = pForkHandle->pOps->pfnDuplicatePages(pModule->pvDataBase, pModule->pvDataEnd, __LIBC_FORK_ONLY_DIRTY);
340	if (rc)
341	return rc; /* failure */
342
343	Prototypes:
344	/**
345	* Duplicating a number of pages from pvStart to pvEnd.
346	* @returns 0 on success.
347	* @returns appropriate non-zero error code on failure.
348	* @param pForkHandle Handle of the current fork operation.
349	* @param pvStart Pointer to start of the pages. Rounded down.
350	* @param pvEnd Pointer to end of the pages. Rounded up.
351	* @param fFlags __LIBC_FORK_ONLY_DIRTY means checking whether the
352	* pages are actually dirty before bothering touching
353	* and copying them. (Using the partically broken
354	* DosQueryMemState() API.)
355	* __LIBC_FORK_ALL means not to bother checking, but
356	* just go ahead copying all the pages.
357	*/
358	int pfnDuplicatePages(__LIBC_FORKHANDLE pForkHandle, void pvStart, void *pvEnd, unsigned fFlags);
359
360	/**
361	* Invoke a function in the child process giving it an chunk of input.
362	* The function is invoked the next time the fork buffer is flushed,
363	* call pfnFlush() if the return code is desired.
364	*
365	* @returns 0 on success.
366	* @returns appropriate non-zero error code on failure.
367	* @param pForkHandle Handle of the current fork operation.
368	* @param pfn Pointer to the function to invoke in the child.
369	* The function gets the fork handle, pointer to
370	* the argument memory chunk and the size of that.
371	* The function must return 0 on success, and non-zero
372	* on failure.
373	* @param pvArg Pointer to a block of memory of size cbArg containing
374	* input to be copied to the child and given to pfn upon
375	* invocation.
376	*/
377	int pfnInvoke(int (pfn)(__LIBC_FORKHANDLE pForkHandle, void pvArg, size_t cbArg), void pvArg, size_t cbArg);
378
379	/**
380	* Flush the fork() buffer. Meaning taking what ever is in the fork buffer
381	* and let the child process it.
382	* This might be desired to get the result of a pfnInvoke() in a near
383	* synchornous way.
384	* @returns 0 on success.
385	* @returns appropriate non-zero error code on failure.
386	* @param pForkHandle Handle of the current fork operation.
387	*/
388	int pfnFlush(__LIBC_FORKHANDLE *pForkHandle);
389
390	/**
391	* Register a fork() completion callback.
392	*
393	* Use this primitive to do post fork() cleanup.
394	* The callbacks are executed first in the child, then in the parent.
395	*
396	* @returns 0 on success.
397	* @returns appropriate non-zero error code on failure. (Usually ENOMEM.)
398	* @param pForkHandle Handle of the current fork operation.
399	* @param pfnCallback Pointer to the function to call back.
400	* This will be called when fork() is about to
401	* complete (the fork() result is established so to
402	* speak). A zero rc argument indicates success,
403	* a non zero rc argument indicates failure.
404	* @param pvArg Argument to pass to pfnCallback as 3rd argument.
405	* @param enmContext __LIBC_FORKCTX_CHILD, __LIBC_FORKCTX_PARENT, or
406	* __LIBC_FORKCTX_BOTH.
407	* (mental note: check up the naming convention for enums!)
408	* @remark Use with care, the memory used to remember these is taken from the
409	* fork buffer.
410	*/
411	int pfnCompletionCallback(__LIBC_FORKHANDLE *pForkHandle,
412	void (pfnCallback)(__LIBC_FORKHANDLE , int rc, void pvArg), void *pvArg,
413	__LIBC_PARENTCHILDCTX enmContext);
414	...
415
416
417
418	4.3 The Flow Of A fork() Operation
419	----------------------------------
420
421	When a process simple process foo.exe calls fork() the following events occur.
422	(The 'p:) indicates parent process while (c) indicates child process.):
423
424	- p: fork() is called. It starts by push all registers (including fpu)
425	onto the stack and recording the address of that stuff (in the
426	fork handle when it's initiated).
427	- p: fork() allocates the shared fork memory and initiatlizes it, thus
428	creating the fork handle.
429	- p: fork() calls helper for copying the memory allocations records
430	to the fork buffer. (Those are FIFO and if there are too many for
431	the fork buffer they should be completed after DosExecPgm returns.)
432	- p: fork() walks the list of registered modules and calls the callback
433	function asking if it's ok to fork now.
434	Note: This will work for processes with multiple libc dlls because
435	the list head is in the process block.
436	- p: fork() allocates and initiates the process block of the child process
437	entering the fork handle and linking it into the embryo list.
438	- p: fork() takes the exec semaphore.
439	- p: fork() spawns a child process taking the executable name from the PIB
440	and giving it "!fork!" as argument.
441	- c: During DosExecPgm all dll0(hi)fork's will be called, and for forkable
442	modules __libc_ForkRegisterModule() is called and returns 1. The
443	init code will the return successfully and not call the _DLL_InitTerm()
444	or any other DLL init code.
445	- c: __libc_ForkRegisterModule() will first check if the process block
446	have been found (global LIBC pointer), and if not try locate it
447	or allocate a new one. It will the check the fork handle.
448	Once found it will add the module to the list of forkable modules.
449	If the fork handle member is not NULL a fork operation is in
450	progress and the module callback is called with a check if the
451	module still thing fork is ok and give it a chance to do dllinit
452	time preperations.
453	The operations returns 1 if we're working, 0 if we're not working
454	and -1 if we failed in some way the the dllinit should fail.
455	- c: The first time the process block is found and it's forking
456	a helper for processing the memory allocations in the
457	for buffer is called.
458	This must be done as early as possible!!!
459	- p: The child have successfully initiated, DosExecPgm/DosStartSession
460	returns NO_ERROR.
461	- c: Child blocks while trying to get access to the fork handle (crt0).
462	(Blocks on fork handle child event semaphore.)
463	- p: Parent sets the operation enum member of the fork handle to signal
464	an init operation. It resets the parent event sem member, releases
465	the mutex, and goes to sleep for a defined max fork() timeout on the
466	event sem. (The max could be, let's say, 30 seconds.)
467	- c: The child get the ownership of the fork handle mutex.
468	- c: If the process is statically linked the memory allocations should
469	be done now (meaning do it here if not done already).
470	- c: The child resets the child event sem, posts the parent event sem
471	and releases the mutex.
472	- p: fork() acquires the fork handle ownership and checks the return code
473	from the child.
474	- p: fork() walks the list of modules calling the callbacks with the
475	do parent fork operation. This means the each register module will
476	do what's necessary for replicting it self into the child process
477	so that it will work as expected there after the fork() returns.
478	This is done using the primitives. This is the only time the
479	parent can use the currently defined primitives.
480	- p: Buffer flush is preformed. This may happen multiple times, but
481	fork() will allways finish of by doing one after all callbacks
482	have been called.
483	The buffer flush means passing the current fork buffer content
484	to the child for processing. pfnFlush() does this.
485	- p: pfnFlush() sets the fork handle operation enum to
486	process buffer, resets the parent event sem, signals the
487	child event semaphore and releases the mutex.
488	- c: Child takes ownership of the fork handle and performs
489	the actions recorded in the fork buffer.
490	- c: The total result is put in the result member, other stuff
491	might may be put in the buffer but that's currently not
492	defined. The fork buffer is then transfered to the parent.
493	- p: pfnFlush() wakes up and reclaims the fork handle ownership
494	and returns the value of the result member.
495	What it does if the buffer contains data is currently not
496	defined.
497	- p: Once all callbacks have been successfully executed, the stack is
498	copied to the child. We copy all committed stack pages. The fork()
499	return stack address is also passed to the child.
500	NOTE: this step may be relocated to an earlier phase!
501	- c: Child gets the stack and copies it in two turns, first the upper
502	part (above current esp/fork return stack address), then it relocate
503	it self on the stack so that it's ready for returning, before it
504	copies the low part of the stack.
505	(low/high here is not address value but logical stack view.)
506	- c: Iterate the modules calling the callbacks signaling fork child
507	operation. the callbacks then have the option to iterate the
508	_CRT_FORK_CHILD1 vector.
509	- c: Calls any completion callbacks registered.
510	- c: Put's result code and passes the fork handle to parent after first
511	freeing its mapping of the shared memory and semphores (not all sems
512	first of course).
513	- c: Returns from fork() restoring all registers but setting eax (return
514	value) to zero indicating child.
515	- p: fork() calls any completion callbacks registered.
516	- p: fork() frees the fork handle and related resources and returns
517	the pid of the child process. (not restoring registers)
518
519
520
521	4.4 Forking LIBC
522	----------------
523
524	To make LIBC forkable a bunch of things have to be fixed up in the child
525	process. Some of these must be done in a certain order other doesn't have to.
526	To solve this we are using set vectors (as we do for init and term, see
527	emx/startup.h). The fork set vectors are be defined in InnoTekLIBC/fork.h
528	and be called _CRT_FORK_PARENT1() and _CRT_FORK_CHILD1(). They take two
529	arguments, the callback and the priority. Priority is 0 to 4G-1 where 4G-1
530	is the highest priority. The set vectors are started in crt0/dll0 called
531	___crtfork_parent1__, ___crtfork_chidl1__
532
533	The _atfork_callback() iterates the set vectors when called for doing
534	parent and child fork stuff.
535
536
537	The _atfork_callback() have this prototype:
538	/**
539	* Called multiple times during fork() both in the parent and the child.
540	*
541	* The default LIBC implementation will:
542	* 1) schedule the data segment for duplication.
543	* 2) do ordered LIBC fork() stuff.
544	* 3) do unordered LIBC fork() stuff, _CRT_FORK1 vector.
545	*
546	* @returns 0 on success.
547	* @returns appropriate non-zero error code on failure.
548	* @param pModule Pointer to the module record which is being
549	* processed.
550	* @param pForkHandle Handle of the current fork operation.
551	* @param enmOperation Which callback operation this is.
552	* Any value can be used, the implementation
553	* of this function must just respond to the
554	* one it knows and return successfully on the
555	* others.
556	* Operations:
557	* __LIBC_FORK_CHECK_PARENT
558	* __LIBC_FORK_CHECK_CHILD
559	* __LIBC_FORK_FORK_PARENT
560	* __LIBC_FORK_FORK_CHILD
561	*/
562	int _atfork_callback(__LIBC_FORKMODULE pModule, __LIBC_FORKHANDLE pForkHandle,
563	enum __LIBC_CALLBACKOPERATION enmOperation);
564
565	The _CRT_FORK_*1() callbacks have this declaration:
566	/**
567	* Called once in the parent during fork().
568	* This function will use the fork primitives to move data and invoke
569	* functions in the child process.
570	*
571	* @returns 0 on success.
572	* @returns appropriate non-zero error code on failure.
573	* @param pModule Pointer to the module record which is being
574	* processed.
575	* @param pForkHandle Handle of the current fork operation.
576	* @param enmOperation Which callback operation this is.
577	* !Important! Later versions of LIBC may call
578	* this callback more than once. This parameter
579	* will indicate what's going on.
580	*/
581	int _atfork_callback(__LIBC_FORKMODULE pModule, __LIBC_FORKHANDLE pForkHandle,
582	enum __LIBC_CALLBACKOPERATION enmOperation);
583
584
585
586
587	4.4.1 Heap Memory
588	-----------------
589
590	The LIBC heaps will use the extended DosAllocMemEx. This means that the
591	memory used by the heaps will be reserved at LIBC init time and duplicated
592	as the very first thing in the LIBC _atfork_callback().
593
594	4.4.1.1 DosAllocMemEx
595	---------------------
596
597	TODO. Fixed address allocation and allocation recording.
598
599	4.4.1.2 DosFreeMemEx
600	--------------------
601
602	TODO
603
604
605	4.4.2 Semaphores
606	----------------
607
608	Use _CRT_FORK_*1() for each of the LIBC semaphores, or we'll make an extended
609	API, DosCreateEventSemEx/DosCreateMutexSemEx, for semaphores as we do with
610	memory APIs.
611
612	There is a forkable class of semaphores, we might wanna kick that out if
613	we decide to use extended APIs (which I guess we'll do).
614
615
616
617	4.4.3 Filehandles
618	-----------------
619
620	Two imporant things, 1) _all_ handles are inherited (even the close-on-exec ones),
621	and 2) non-OS/2 handles must be inherited too.
622
623	For 1) we must temporarily change the inherit flag on all the close-on-exec
624	flagged handles during the fork.
625	The major question here is when we're gonna restore the OS/2 no inherit flag
626	for close-on-exec handles. The simplest option option is a
627	__LIBC_FORK_DONE_PARENT _atfork_callback() operation. The best option is to
628	have a primitive to registering fork-done routines (which are called both
629	on success and failure).
630
631	For 2) we need to extend the libc filehandle operation interface to include
632	atfork operation. This will be called for every non-standard handle and it
633	must it self use the fork primitives to cause something to happen in the
634	child. This is not the fastest way, but it's the most flexible one and it's
635	one which is probably will work too.
636
637
638	4.4.3.1 Sockets
639	---------------
640
641	Implement the atfork handle operation. Use the fork primitives to invoke
642	a function in the child duplicating that handle. The function invoked in
643	the child basically use adds the socket to the socket list of the new
644	process (tcpip api for this).
645
646	Note that WS4eB tcpip level have a bug in the api adding sockets to a
647	process. The problem is that a socket cannot be added twice, it'll cause
648	an breakpoint instruction.
649
650
651
652	4.4.4 Locale/Iconv/Stuff
653	------------------------
654
655	Record and create once again in the child. Use _CRT_FORK_*1() to register
656	callbacks. Requires a little bit of recording of create parameters in the
657	iconv() case but that's nothing spectacular.
658
659
660
661
662
663	8.0 Coding Conventions
664	----------------------
665
666	New LIBC stuff uses these conventions:
667	- Full usage of hungarian prefixes. Details on this is found in the
668	old odin web pages and gradd docs (IIRC).
669	- As much as possible shall be static. I.e. static int internalhelper(void).
670	- Internal global function and variables shall be prefixed __libc_[a-z] or
671	_sys_ depending on what it implements. Will not be exported by LIBCxy.DLL.
672	- Non-standard LIBC functionality is prefixed __libc_[A-Z].
673	- Stuff defined in SuS is wrapped by _STD() so that we get __std_ prefix
674	and the usual two aliases (plain and underscored).
675	- No warnings.
676
677
678	9.0 Abbreviation and such
679	-------------------------
680
681	SuS
682	The Single Unix Specification version 6 as published on www.opengroup.org.
683
684

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