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-rw-r--r--docs/nofork_noexec.txt25
1 files changed, 17 insertions, 8 deletions
diff --git a/docs/nofork_noexec.txt b/docs/nofork_noexec.txt
index d4abdf452..06c789aff 100644
--- a/docs/nofork_noexec.txt
+++ b/docs/nofork_noexec.txt
@@ -2,7 +2,7 @@
Unix shells traditionally execute some commands internally in the attempt
to dramatically speed up execution. It will be slow as hell if for every
-"echo blah" shell will fork and exec /bin/echo. For this end, shells
+"echo blah" shell will fork and exec /bin/echo. To this end, shells
have to _reimplement_ these commands internally.
Busybox is unique in this regard because it already is a collection
@@ -11,14 +11,20 @@ for speeding up busybox shells, and more. NOEXEC and NOFORK applets
are exactly those applets which are eligible for these tricks.
Applet will be subject to NOFORK/NOEXEC tricks if it is marked as such
-in applets.h. CONFIG_FEATURE_PREFER_APPLETS is a config option which
+in applets.h. FEATURE_PREFER_APPLETS is a config option which
globally enables usage of NOFORK/NOEXEC tricks.
+If it is enabled, FEATURE_SH_STANDALONE can be enabled too,
+and then shells will use NOFORK/NOEXEC tricks for ordinary commands.
+NB: shell builtins use these tricks regardless of FEATURE_SH_STANDALONE
+or FEATURE_PREFER_APPLETS.
-If you want to call a program and wait for it, use spawn_and_wait(argv).
-It will check whether argv[0] is an applet name and will optionally
-do NOFORK/NOEXEC thing.
+In C, if you want to call a program and wait for it, use
+spawn_and_wait(argv), BB_EXECVP(prog,argv) or BB_EXECLP(prog,argv0,...).
+They check whether program name is an applet name and optionally
+do NOFORK/NOEXEC thing depending on configuration.
-NOEXEC
+
+ NOEXEC
NOEXEC applet should work correctly if another applet forks and then
executes exit(<applet>_main(argc,argv)) in the child. The rules
@@ -32,9 +38,10 @@ roughly are:
* ...
NOEXEC applets save only one half of fork+exec overhead.
-NOEXEC trick is disabled for NOMMU compile.
+NOEXEC trick is disabled for NOMMU build.
+
-NOFORK
+ NOFORK
NOFORK applet should work correctly if another applet simply runs
<applet>_main(argc,argv) and then continues with its business (xargs,
@@ -55,6 +62,8 @@ on what applet can/cannot do:
* if you allocate memory, you can use xmalloc() only on the very first
allocation. All other allocations should use malloc[_or_warn]().
After first allocation, you cannot use any xfuncs.
+ Otherwise, failing xfunc will return to caller applet
+ without freeing malloced data!
* All allocated data, opened files, signal handlers, termios settings,
O_NONBLOCK flags etc should be freed/closed/restored prior to return.
* ...