TODO revision 1.8 
1o Call module as module.
2
3  Until now, everything is called as attribute.  Separate module from it:
4
5	- Module is a collection of code (*.[cSo]), and provides a function.
6	  Module can depend on other modules.
7
8	- Attribute provides metadata for modules.  One module can have
9	  multiple attributes.  Attribute doesn't generate a module (*.o,
10	  *.ko).
11
12o Emit everything (ioconf.*, Makefile, ...) per-attribute.
13
14o Generate modular(9) related information.  Especially module dependency.
15
16o Rename "interface attribute" to "bus".
17
18  Instead of
19
20	define	audiobus {}
21	attach	audio at audiobus
22
23  Do like this
24
25	defbus	audiobus {}
26	attach	audio at audiobus
27
28o Retire "attach foo at bar with foo_bar.c"
29
30  Most of these should be rewritten by defining a common interface attribute
31  "foobus", instead of writing multiple attachments.  com(4), ld(4), ehci(4)
32  are typical examples.  For ehci(4), EHCI-capable controller drivers implement
33  "ehcibus" interface, like:
34
35	defne	ehcibus {}
36	device	imxehci: ehcibus
37
38  These drivers' attach functions call config_found() to attach ehci(4) via
39  the "ehcibus" interface attribute, instead of calling ehci_init() directly.
40  Same for com(4) (com_attach_subr()) and ld(4) (ldattach()).
41
42o Sort objects in more reasonable order.
43
44  Put machdep.ko in the lowest address.  uvm.ko and kern.ko follow.
45
46  Kill alphabetical sort (${OBJS:O} in sys/conf/Makefile.inc.kern.
47
48  Use ldscript.  Do like this
49
50	.text :
51	AT (ADDR(.text) & 0x0fffffff)
52	{
53	  *(.text.machdep.locore.entry)
54	  *(.text.machdep.locore)
55	  *(.text.machdep)
56	  *(.text)
57	  *(.text.*)
58	  :
59
60  Kill linker definitions in sys/conf/Makefile.inc.kern.
61
62o Differentiate "options" and "flags"/"params".
63
64  "options" enables features by adding *.c files (via attributes).
65
66  "flags" and "params" are to change contents of *.c files.  These don't add
67  *.c files to the result kernel, or don't build attributes (modules).
68
69o Make flags/params per attributes (modules).
70
71  Basically flags and params are cpp(1) #define's generated in opt_*.h.  Make
72  them local to one attributes (modules).  Flags/params which affects files
73  across attributes (modules) are possible, but should be discouraged.
74
75o Generate things only by definitions.
76
77  In the ideal dynamically modular world, "selection" will be done not at
78  compile time but at runtime.  Users select their wanted modules, by
79  dynamically loading them.
80
81  This means that the system provides all choices; that is, build all modules
82  in the source tree.  Necessary information is defined in the "definition"
83  part.
84
85o Split cfdata.
86
87  cfdata is a set of pattern matching rules to enable devices at runtime device
88  auto-configuration.  It is pure data and can (should) be generated separately
89  from the code.
90
91o Allow easier adding and removing of options.
92
93  It should be possible to add or remove options, flags, etc.,
94  without regard to whether or not they are already defined.
95  For example, a configuration like this:
96
97	include GENERIC
98	options FOO
99	no options BAR
100
101  should work regardless of whether or not options FOO and/or
102  options BAR were defined in GENERIC.  It should not give
103  errors like "options BAR was already defined" or "options FOO
104  was not defined".
105
106o Introduce "class".
107
108  Every module should be classified as at least one class, as modular(9)
109  modules already do.  For example, file systems are marked as "vfs", network
110  protocols are "netproto".
111
112  Consider to merge "devclass" into "class".
113
114  For syntax clarity, class names could be used as a keyword to select the
115  class's instance module:
116
117	# Define net80211 module as netproto class
118	class netproto
119	define net80211: netproto
120
121	# Select net80211 to be builtin
122	netproto net80211
123
124  Accordingly device/attach selection syntax should be revisited.
125
126o Support kernel constructor/destructor (.kctors/.kdtors)
127
128  Initialization and finalization should be called via constructors and
129  destructors.  Don't hardcode those sequences as sys/kern/init_main.c:main()
130  does.
131
132  The order of .kctors/.kdtors is resolved by dependency.  The difference from
133  userland is that in kernel depended ones are located in lower addresses;
134  "machdep" module is the lowest.  Thus the lowest entry in .ctors must be
135  executed the first.
136
137  The .kctors/.kdtors entries are executed by kernel's main() function, unlike
138  userland where start code executes .ctors/.dtors before main().  The hardcoded
139  sequence of various subsystem initializations in init_main.c:main() will be
140  replaced by an array of .kctors invocations, and #ifdef's there will be gone.
141
142o Replace linkset.
143
144  Don't allow kernel subsystems create random ELF sections (with potentially
145  long names) in the final kernel.  To collect some data in statically linked
146  modules, creating intermediate sections (e.g. .data.linkset.sysctl) and
147  exporting the start/end symbols (e.g. _data_linkset_sysctl_{start,end})
148  using linker script should be fine.
149
150  Dynamically loaded modules have to register those entries via constructors
151  (functions).  This means that dynamically loaded modules are flexible but
152  come with overhead.
153
154o Shared kernel objects.
155
156  Since NetBSD has not established a clear kernel ABI, every single kernel
157  has to build all the objects by their own.  As a result, similar kernels
158  (e.g. evbarm kernels) repeatedly compile similar objects, that is waste of
159  energy & space.
160
161  Share them if possible.  For evb* ports, ideally everything except machdep.ko
162  should be shared.
163
164  While leaving optimizations as options (CPU specific optimizations, inlined
165  bus_space(9) operations, etc.) for users, the official binaries build
166  provided by TNF should be as portable as possible.
167