hush: fix comments, no code changes
This commit is contained in:
Denis Vlasenko
parent
422cd7c81c
commit
7b830e78f2
65
shell/hush.c
65
shell/hush.c
@ -753,14 +753,14 @@ static void free_strings(char **strings)
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/* Basic theory of signal handling in shell
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* ========================================
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* This does not describe what hush does, rahter, it is current understanding
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* what it _should_ do.
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* This does not describe what hush does, rather, it is current understanding
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* what it _should_ do. If it doesn't, it's a bug.
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* http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#trap
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*
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* Signals are handled only after each pipe ("cmd | cmd | cmd" thing)
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* is finished or backgrounded. It is the same in interactive and
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* non-interactive shells, and is the same regardless of whether
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* a user trap handler is installed or a default one is in effect.
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* a user trap handler is installed or a shell special one is in effect.
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* ^C or ^Z from keyboard seem to execute "at once" because it usually
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* backgrounds (i.e. stops) or kills all members of currently running
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* pipe.
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@ -770,33 +770,38 @@ static void free_strings(char **strings)
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*
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* Trap handlers will execute even within trap handlers. (right?)
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*
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* User trap handlers are forgotten when subshell is entered.
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* User trap handlers are forgotten when subshell ("(cmd)") is entered. [TODO]
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*
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* If job control is off, backgrounded commands ("cmd &")
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* have SIGINT, SIGQUIT set to SIG_IGN.
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* have SIGINT, SIGQUIT set to SIG_IGN.
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*
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* Commands run in command substitution ("`cmd`")
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* have SIGTTIN, SIGTTOU, SIGTSTP set to SIG_IGN.
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* have SIGTTIN, SIGTTOU, SIGTSTP set to SIG_IGN.
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*
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* Ordinary commands have IGN/DFL set as inherited by the shell
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* from its parent.
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* Ordinary commands have signals set to SIG_IGN/DFL set as inherited
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* by the shell from its parent.
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*
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* Default handlers which differ from DFL action
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* (note: subshell is not an interactive shell):
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* Siganls which differ from SIG_DFL action
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* (note: child (i.e., [v]forked) shell is not an interactive shell):
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*
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* SIGQUIT: ignore
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* SIGTERM (interactive): ignore
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* SUGHUP (interactive): send SIGCONT to stopped jobs,
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* send SIGHUP to all jobs and exit
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* SIGHUP (interactive):
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* send SIGCONT to stopped jobs, send SIGHUP to all jobs and exit
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* SIGTTIN, SIGTTOU, SIGTSTP (if job control is on): ignore
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* (note that ^Z is handled not by trapping SIGTSTP, but by seeing
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* that all pipe members are stopped) (right?)
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* (note that ^Z is handled not by trapping SIGTSTP, but by seeing
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* that all pipe members are stopped) (right?)
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* SIGINT (interactive): wait for last pipe, ignore the rest
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* of the command line, show prompt. (check/expand this)
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* Example 1: this waits 5 sec, but does not execute ls:
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* "echo $$; sleep 5; ls -l" + "kill -INT <pid>"
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* Example 2: this does not wait and does not execute ls:
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* "echo $$; sleep 5 & wait; ls -l" + "kill -INT <pid>"
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* of the command line, show prompt. NB: ^C does not send SIGINT
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* to interactive shell while shell is waiting for a pipe,
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* since shell is bg'ed (is not in foreground process group).
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* (check/expand this)
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* Example 1: this waits 5 sec, but does not execute ls:
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* "echo $$; sleep 5; ls -l" + "kill -INT <pid>"
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* Example 2: this does not wait and does not execute ls:
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* "echo $$; sleep 5 & wait; ls -l" + "kill -INT <pid>"
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* Example 3: this does not wait 5 sec, but executes ls:
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* "sleep 5; ls -l" + press ^C
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*
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* (What happens to signals which are IGN on shell start?)
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* (What happens with signal mask on shell start?)
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@ -813,14 +818,16 @@ static void free_strings(char **strings)
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* unsigned non_DFL_mask: a mask of such "special" signals
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* sigset_t blocked_set: current blocked signal set
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*
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* "trap - SIGxxx": clear bit in blocked_set unless it is also in non_DFL
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* "trap 'cmd' SIGxxx": set bit in blocked_set (even if 'cmd' is '')
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* "trap - SIGxxx":
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* clear bit in blocked_set unless it is also in non_DFL
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* "trap 'cmd' SIGxxx":
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* set bit in blocked_set (even if 'cmd' is '')
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* after [v]fork, if we plan to be a shell:
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* nothing for {} subshell (say, "true | { true; true; } | true")
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* unset all traps if () shell. [TODO]
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* nothing for {} child shell (say, "true | { true; true; } | true")
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* unset all traps if () shell. [TODO]
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* after [v]fork, if we plan to exec:
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* POSIX says pending signal mask is cleared in child - no need to clear it.
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* restore blocked signal set to one inherited by shell just prior to exec.
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* POSIX says pending signal mask is cleared in child - no need to clear it.
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* Restore blocked signal set to one inherited by shell just prior to exec.
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*
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* Note: as a result, we do not use signal handlers much. The only use
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* is to restore terminal pgrp on exit.
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@ -848,7 +855,6 @@ static void init_signal_mask(void)
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#endif
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G.non_DFL_mask = mask;
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/*sigemptyset(&G.blocked_set); - already is */
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sigprocmask(SIG_SETMASK, NULL, &G.blocked_set);
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sig = 0;
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while (mask) {
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@ -859,6 +865,7 @@ static void init_signal_mask(void)
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}
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sigprocmask(SIG_SETMASK, &G.blocked_set, &G.inherited_set);
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}
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static void check_and_run_traps(void)
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{
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static const struct timespec zero_ts = { 0, 0 };
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@ -910,7 +917,7 @@ static void sigexit(int sig)
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#if ENABLE_HUSH_INTERACTIVE
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/* Careful: we can end up here after [v]fork. Do not restore
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* tty pgrp, only top-level shell process does that */
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* tty pgrp then, only top-level shell process does that */
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if (G.interactive_fd && getpid() == G.root_pid)
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tcsetpgrp(G.interactive_fd, G.saved_tty_pgrp);
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#endif
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@ -931,11 +938,11 @@ static void maybe_set_sighandler(int sig)
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*/
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if (!((G.non_DFL_mask >> sig) & 1)) {
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handler = signal(sig, sigexit);
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if (handler == SIG_IGN) /* restore back to IGN! */
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if (handler == SIG_IGN) /* oops... restore back to IGN! */
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signal(sig, handler);
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}
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}
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/* Used only to set handler to restore pgrp on exit, and to reset it to DFL */
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/* Used only to set handler to restore pgrp on exit */
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static void set_fatal_signals_to_sigexit(void)
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{
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if (HUSH_DEBUG) {
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