diff options
| -rw-r--r-- | coreutils/Config.in | 6 | ||||
| -rw-r--r-- | coreutils/Kbuild | 1 | ||||
| -rw-r--r-- | docs/nofork_noexec.txt | 25 | ||||
| -rw-r--r-- | include/applets.h | 1 | ||||
| -rw-r--r-- | include/usage.h | 5 |
5 files changed, 30 insertions, 8 deletions
diff --git a/coreutils/Config.in b/coreutils/Config.in index d3cbc42..3b3f7b3 100644 --- a/coreutils/Config.in +++ b/coreutils/Config.in @@ -579,6 +579,12 @@ config SYNC help sync is used to flush filesystem buffers. +config TAC + bool "tac" + default n + help + tac is used to concatenate and print files in reverse. + config TAIL bool "tail" default n diff --git a/coreutils/Kbuild b/coreutils/Kbuild index ce21b3a..8ada8b0 100644 --- a/coreutils/Kbuild +++ b/coreutils/Kbuild @@ -66,6 +66,7 @@ lib-$(CONFIG_STAT) += stat.o lib-$(CONFIG_STTY) += stty.o lib-$(CONFIG_SUM) += sum.o lib-$(CONFIG_SYNC) += sync.o +lib-$(CONFIG_TAC) += tac.o lib-$(CONFIG_TAIL) += tail.o lib-$(CONFIG_TEE) += tee.o lib-$(CONFIG_TEST) += test.o diff --git a/docs/nofork_noexec.txt b/docs/nofork_noexec.txt index d4abdf4..06c789a 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. * ... diff --git a/include/applets.h b/include/applets.h index c6331cb..4934d18 100644 --- a/include/applets.h +++ b/include/applets.h @@ -334,6 +334,7 @@ USE_SWITCH_ROOT(APPLET(switch_root, _BB_DIR_SBIN, _BB_SUID_NEVER)) USE_SYNC(APPLET_NOFORK(sync, sync, _BB_DIR_BIN, _BB_SUID_NEVER, sync)) USE_BB_SYSCTL(APPLET(sysctl, _BB_DIR_SBIN, _BB_SUID_NEVER)) USE_SYSLOGD(APPLET(syslogd, _BB_DIR_SBIN, _BB_SUID_NEVER)) +USE_TAC(APPLET_NOEXEC(tac, tac, _BB_DIR_USR_BIN, _BB_SUID_NEVER, tac)) USE_TAIL(APPLET(tail, _BB_DIR_USR_BIN, _BB_SUID_NEVER)) USE_TAR(APPLET(tar, _BB_DIR_BIN, _BB_SUID_NEVER)) USE_TASKSET(APPLET(taskset, _BB_DIR_USR_BIN, _BB_SUID_NEVER)) diff --git a/include/usage.h b/include/usage.h index 12d2cef..464fb61 100644 --- a/include/usage.h +++ b/include/usage.h @@ -3542,6 +3542,11 @@ USE_FEATURE_RUN_PARTS_FANCY("\n -l Prints names of all matching files even when "$ syslogd -R masterlog:514\n" \ "$ syslogd -R 192.168.1.1:601\n" +#define tac_trivial_usage \ + "[FILE]..." +#define tac_full_usage \ + "Concatenates FILE(s) and prints them to stdout in reverse" + #define tail_trivial_usage \ "[OPTION]... [FILE]..." #define tail_full_usage \ |