TODO revision 1.5 
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 Sort objects in more reasonable order.
29
30  Put machdep.ko in the lowest address.  uvm.ko and kern.ko follow.
31
32  Kill alphabetical sort (${OBJS:O} in sys/conf/Makefile.inc.kern.
33
34  Use ldscript.  Do like this
35
36	.text :
37	AT (ADDR(.text) & 0x0fffffff)
38	{
39	  *(.text.machdep.locore.entry)
40	  *(.text.machdep.locore)
41	  *(.text.machdep)
42	  *(.text)
43	  *(.text.*)
44	  :
45
46  Kill linker definitions in sys/conf/Makefile.inc.kern.
47
48o Differentiate "options" and "flags"/"params".
49
50  "options" enables features by adding *.c files (via attributes).
51
52  "flags" and "params" are to change contents of *.c files.  These don't add
53  *.c files to the result kernel, or don't build attributes (modules).
54
55o Make flags/params per attributes (modules).
56
57  Basically flags and params are cpp(1) #define's generated in opt_*.h.  Make
58  them local to one attributes (modules).  Flags/params which affects files
59  across attributes (modules) are possible, but should be discouraged.
60
61o Generate things only by definitions.
62
63  In the ideal dynamically modular world, "selection" will be done not at
64  compile time but at runtime.  Users select their wanted modules, by
65  dynamically loading them.
66
67  This means that the system provides all choices; that is, build all modules
68  in the source tree.  Necessary information is defined in the "definition"
69  part.
70
71o Split cfdata.
72
73  cfdata is pattern matching rules to enable devices at runtime device
74  auto-configuration.  It is pure data and can (should) be generated separately
75  from the code.
76
77o Allow easier adding and removing of options.
78
79  It should be possible to add or remove options, flags, etc.,
80  without regard to whether or not they are already defined.
81  For example, a configuration like this:
82
83	include GENERIC
84	options FOO
85	no options BAR
86
87  should work regardless of whether or not options FOO and/or
88  options BAR were defined in GENERIC.  It should not give
89  errors like "options BAR was already defined" or "options FOO
90  was not defined".
91
92o Introduce "class".
93
94  Every module should be classfied as at least one class, as modular(9)
95  modules already do.  For example, filesystems are marked as "vfs", network
96  protocols are "netproto".
97
98  Consider to merge "devclass" into "class".
99
100  For syntax clarity, class names could be used as a keyword to select the
101  class's instance module:
102
103	# Define net80211 module as netproto class
104	class netproto
105	define net80211: netproto
106
107	# Select net80211 to be builtin
108	netproto net80211
109
110  Accordingly device/attach selection syntax should be revisited.
111
112o Support kernel constructor/destructor (.ctors/.dtors)
113
114  Initialization and finalization should be called via constructors and
115  destructors.  Don't hardcode those sequences as sys/kern/init_main.c:main()
116  does.
117
118  The order of .ctors/.dtors is resolved by dependency.  The difference from
119  userland is that in kernel depended ones are located in lower addresses;
120  "machdep" module is the lowest.  Thus the lowest entry in .ctors must be
121  executed the first.
122
123o Replace linkset.
124
125  Don't allow kernel subsystems create random ELF sections (with potentially
126  long names) in the final kernel.  To collect some data in statically linked
127  modules, creating intermediate sections (e.g. .data.linkset.sysctl) and
128  exporting the start/end symbols (e.g. _data_linkset_sysctl_{start,end})
129  using linker script should be fine.
130
131  Dynamically loaded modules have to register those entries via constructors
132  (functions).  This means that dynamically loaded modules are flexible but
133  come with overhead.
134