bcd5fc12e
Denis Vlasenko
2008-01-06
Subject
tac: new applet. ~240 bytes.
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Commit Diff GitHub →
coreutils/Config.in +6 -0coreutils/Kbuild +1 -0docs/nofork_noexec.txt +17 -8include/applets.h +1 -0include/usage.h +5 -0
coreutils/Config.in+6 -0
| @@ -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 | |
coreutils/Kbuild+1 -0
| @@ -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 | |
docs/nofork_noexec.txt+17 -8
| @@ -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. | |
| * ... | |
include/applets.h+1 -0
| @@ -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)) | |
include/usage.h+5 -0
| @@ -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 \ | |