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link: new applet

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coreutils grew itself a tiny simplistic alternative to ln:

	Usage: link FILE LINK

	Create hard LINK to FILE

function                                             old     new   delta
link_main                                              -      75     +75
packed_usage                                       31114   31131     +17
applet_names                                        2564    2569      +5
applet_main                                         1480    1484      +4
applet_install_loc                                   185     186      +1
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(add/remove: 1/0 grow/shrink: 4/0 up/down: 102/0)             Total: 102 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
2017-01-26 00:27:53 +01:00
parent 7dd906a388
commit 06f20bf675
3 changed files with 72 additions and 9 deletions
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34
docs/nofork_noexec.txt
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@@ -33,6 +33,7 @@ roughly are:
* do not expect shared global variables/buffers to be in their
"initialized" state. Examples: xfunc_error_retval can be != 1,
bb_common_bufsiz1 can be scribbled over, ...
(although usually xfunc_error_retval's state is not a problem).
* do not expect that stdio wasn't used before. Calling set[v]buf()
can be disastrous.
* ...
@@ -81,18 +82,37 @@ are probably not worth the effort.
Any NOFORK applet is also a NOEXEC applet.
Calling NOFORK applets
API to call NOFORK applets is two functions:
run_nofork_applet(appno, argv)
spawn_and_wait(argv) // only if FEATURE_PREFER_APPLETS=y
First one is directly used by shells if FEATURE_SH_NOFORK=y.
Second one is used by many applets, but main users are xargs and find.
It itself calls run_nofork_applet(), if argv[0] turned out to be a name
of a NOFORK applet.
run_nofork_applet() saves/inits/restores option parsing, xfunc_error_retval,
applet_name. Thus, for example, caller does not need to worry about
option_mask32 getting trashed.
Relevant CONFIG options
FEATURE_PREFER_APPLETS
BB_EXECVP(cmd, argv) will try to exec /proc/self/exe
if command's name matches some applet name
applet tables will contain NOFORK/NOEXEC bits
if command's name matches some applet name;
spawn_and_wait(argv) will do NOFORK/NOEXEC tricks
FEATURE_SH_STANDALONE (needs FEATURE_PREFER_APPLETS=y)
shells will try to exec /proc/self/exe if command's name matches
some applet name
shells will do NOEXEC trick on NOEXEC applets
//TODO: the above two things probably should have separate options?
FEATURE_SH_NOFORK (needs FEATURE_PREFER_APPLETS=y)
FEATURE_SH_STANDALONE
shells will try to exec /proc/self/exe if command's name matches
some applet name; shells will do NOEXEC trick on NOEXEC applets
//TODO: split (same as for PREFER_APPLETS)
FEATURE_SH_NOFORK
shells will do NOFORK trick on NOFORK applets