view Documentation/smart-config.txt @ 452:c7ed6fe5dca0

kexec: dont initialise regions in reserve_memory()

There is no need to initialise efi_memmap_res and boot_param_res in
reserve_memory() for the initial xen domain as it is done in
machine_kexec_setup_resources() using values from the kexec hypercall.

Signed-off-by: Simon Horman <horms@verge.net.au>
author Keir Fraser <keir.fraser@citrix.com>
date Thu Feb 28 10:55:18 2008 +0000 (2008-02-28)
parents 831230e53067
line source
1 Smart CONFIG_* Dependencies
2 1 August 1999
4 Michael Chastain <mec@shout.net>
5 Werner Almesberger <almesber@lrc.di.epfl.ch>
6 Martin von Loewis <martin@mira.isdn.cs.tu-berlin.de>
8 Here is the problem:
10 Suppose that drivers/net/foo.c has the following lines:
12 #include <linux/config.h>
14 ...
17 /* Code for auto-frobbing */
18 #else
19 /* Manual frobbing only */
20 #endif
22 ...
25 /* Code for model two */
26 #endif
28 Now suppose the user (the person building kernels) reconfigures the
29 kernel to change some unrelated setting. This will regenerate the
30 file include/linux/autoconf.h, which will cause include/linux/config.h
31 to be out of date, which will cause drivers/net/foo.c to be recompiled.
33 Most kernel sources, perhaps 80% of them, have at least one CONFIG_*
34 dependency somewhere. So changing _any_ CONFIG_* setting requires
35 almost _all_ of the kernel to be recompiled.
37 Here is the solution:
39 We've made the dependency generator, mkdep.c, smarter. Instead of
40 generating this dependency:
42 drivers/net/foo.c: include/linux/config.h
44 It now generates these dependencies:
46 drivers/net/foo.c: \
47 include/config/foo/autofrob.h \
48 include/config/foo/model/two.h
50 So drivers/net/foo.c depends only on the CONFIG_* lines that
51 it actually uses.
53 A new program, split-include.c, runs at the beginning of
54 compilation (make bzImage or make zImage). split-include reads
55 include/linux/autoconf.h and updates the include/config/ tree,
56 writing one file per option. It updates only the files for options
57 that have changed.
59 Flag Dependencies
61 Martin Von Loewis contributed another feature to this patch:
62 'flag dependencies'. The idea is that a .o file depends on
63 the compilation flags used to build it. The file foo.o has
64 its flags stored in .flags.foo.o.
66 Suppose the user changes the foo driver from resident to modular.
67 'make' will notice that the current foo.o was not compiled with
68 -DMODULE and will recompile foo.c.
70 All .o files made from C source have flag dependencies. So do .o
71 files made with ld, and .a files made with ar. However, .o files
72 made from assembly source do not have flag dependencies (nobody
73 needs this yet, but it would be good to fix).
75 Per-source-file Flags
77 Flag dependencies also work with per-source-file flags.
78 You can specify compilation flags for individual source files
79 like this:
83 This helps clean up drivers/net/Makefile, drivers/scsi/Makefile,
84 and several other Makefiles.
86 Credit
88 Werner Almesberger had the original idea and wrote the first
89 version of this patch.
91 Michael Chastain picked it up and continued development. He is
92 now the principal author and maintainer. Please report any bugs
93 to him.
95 Martin von Loewis wrote flag dependencies, with some modifications
96 by Michael Chastain.
98 Thanks to all of the beta testers.