diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/nofork_noexec.txt | 25 |
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. * ... |