Date: Sat, 13 Oct 2001 17:43:39 +0200 From: Vadim Vygonets <vadik-hackers@freebsd.vygo.net> To: freebsd-hackers@freebsd.org Subject: loader.conf conditional assignment Message-ID: <20011013174339.A21230@cs.huji.ac.il>
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We are working on integration of network-booted FreeBSD system to
our envoronment. Naturally, different machines need different
kernels, so we pass the kernel paramater in DHCP response.
However, it gets overwritten in /boot/defaults/loader.conf. We
decided that commenting out the assignment of 'kernel' and
'kernel_options' is not what we want, because we want both to use
the default value and to be able to override it via DHCP.
After taking some time to learn Forth (interesting language, I
must say) and a false start (involving saving environment
variables (names and values) in a linked list and restoring them
after the assignment), I decided to use the Makefile syntax of ?=
to set an environment variable if it's not set yet, so it will be
possible to say:
kernel?="/kernel"
In this case, if kernel is set via DHCP, the value is not
changed, but if it's not, it becomes "/kernel". Attached is the
patch for /boot/support.4th against the version in FreeBSD 4.4.
Vadik.
--
Bell Labs Unix -- Reach out and grep someone.
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--- ../../4.4/boot/support.4th Thu Aug 9 08:52:20 2001
+++ support.4th Thu Oct 11 20:11:29 2001
@@ -190,6 +190,9 @@
string name_buffer
string value_buffer
+variable assignment_op
+char = constant regular_assignment
+char ? constant notdef_assignment
\ File data temporary storage
@@ -331,6 +334,10 @@
line_pointer c@ [char] = =
;
+: question_mark?
+ line_pointer c@ [char] ? =
+;
+
: comment?
line_pointer c@ [char] # =
;
@@ -464,8 +471,16 @@
['] white_space_3 to parsing_function
;
+: question_mark
+ notdef_assignment assignment_op !
+ skip_character
+ assignment_sign? if ['] assignment_sign to parsing_function exit then
+ syntax_error throw
+;
+
: white_space_2
eat_space
+ question_mark? if ['] question_mark to parsing_function exit then
assignment_sign? if ['] assignment_sign to parsing_function exit then
syntax_error throw
;
@@ -554,6 +569,10 @@
module_loaderror_suffix suffix_type?
;
+: notdef_assignment?
+ assignment_op @ notdef_assignment =
+;
+
: set_conf_files
conf_files .addr @ ?dup if
free-memory
@@ -717,6 +736,14 @@
then
;
+: set_environment_variable_if_notdef
+ name_buffer .addr @ name_buffer .len @ getenv -1 = if
+ set_environment_variable
+ else
+ drop
+ then
+;
+
: set_verbose
yes_value? to verbose?
;
@@ -754,6 +781,7 @@
module_beforeload? if set_module_beforeload exit then
module_afterload? if set_module_afterload exit then
module_loaderror? if set_module_loaderror exit then
+ notdef_assignment? if set_environment_variable_if_notdef exit then
set_environment_variable
;
@@ -775,6 +803,7 @@
0 name_buffer .len !
0 value_buffer .addr !
0 value_buffer .len !
+ regular_assignment assignment_op !
;
\ Higher level file processing
--fUYQa+Pmc3FrFX/N--
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