diff options
| -rw-r--r-- | shell/hush.c | 65 |
1 files changed, 36 insertions, 29 deletions
diff --git a/shell/hush.c b/shell/hush.c index 21fa95429..a96b179c6 100644 --- a/shell/hush.c +++ b/shell/hush.c @@ -753,14 +753,14 @@ static void free_strings(char **strings) /* Basic theory of signal handling in shell * ======================================== - * This does not describe what hush does, rahter, it is current understanding - * what it _should_ do. + * This does not describe what hush does, rather, it is current understanding + * what it _should_ do. If it doesn't, it's a bug. * http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#trap * * Signals are handled only after each pipe ("cmd | cmd | cmd" thing) * is finished or backgrounded. It is the same in interactive and * non-interactive shells, and is the same regardless of whether - * a user trap handler is installed or a default one is in effect. + * a user trap handler is installed or a shell special one is in effect. * ^C or ^Z from keyboard seem to execute "at once" because it usually * backgrounds (i.e. stops) or kills all members of currently running * pipe. @@ -770,33 +770,38 @@ static void free_strings(char **strings) * * Trap handlers will execute even within trap handlers. (right?) * - * User trap handlers are forgotten when subshell is entered. + * User trap handlers are forgotten when subshell ("(cmd)") is entered. [TODO] * * If job control is off, backgrounded commands ("cmd &") - * have SIGINT, SIGQUIT set to SIG_IGN. + * have SIGINT, SIGQUIT set to SIG_IGN. * * Commands run in command substitution ("`cmd`") - * have SIGTTIN, SIGTTOU, SIGTSTP set to SIG_IGN. + * have SIGTTIN, SIGTTOU, SIGTSTP set to SIG_IGN. * - * Ordinary commands have IGN/DFL set as inherited by the shell - * from its parent. + * Ordinary commands have signals set to SIG_IGN/DFL set as inherited + * by the shell from its parent. * - * Default handlers which differ from DFL action - * (note: subshell is not an interactive shell): + * Siganls which differ from SIG_DFL action + * (note: child (i.e., [v]forked) shell is not an interactive shell): * * SIGQUIT: ignore * SIGTERM (interactive): ignore - * SUGHUP (interactive): send SIGCONT to stopped jobs, - * send SIGHUP to all jobs and exit + * SIGHUP (interactive): + * send SIGCONT to stopped jobs, send SIGHUP to all jobs and exit * SIGTTIN, SIGTTOU, SIGTSTP (if job control is on): ignore - * (note that ^Z is handled not by trapping SIGTSTP, but by seeing - * that all pipe members are stopped) (right?) + * (note that ^Z is handled not by trapping SIGTSTP, but by seeing + * that all pipe members are stopped) (right?) * SIGINT (interactive): wait for last pipe, ignore the rest - * of the command line, show prompt. (check/expand this) - * Example 1: this waits 5 sec, but does not execute ls: - * "echo $$; sleep 5; ls -l" + "kill -INT <pid>" - * Example 2: this does not wait and does not execute ls: - * "echo $$; sleep 5 & wait; ls -l" + "kill -INT <pid>" + * of the command line, show prompt. NB: ^C does not send SIGINT + * to interactive shell while shell is waiting for a pipe, + * since shell is bg'ed (is not in foreground process group). + * (check/expand this) + * Example 1: this waits 5 sec, but does not execute ls: + * "echo $$; sleep 5; ls -l" + "kill -INT <pid>" + * Example 2: this does not wait and does not execute ls: + * "echo $$; sleep 5 & wait; ls -l" + "kill -INT <pid>" + * Example 3: this does not wait 5 sec, but executes ls: + * "sleep 5; ls -l" + press ^C * * (What happens to signals which are IGN on shell start?) * (What happens with signal mask on shell start?) @@ -813,14 +818,16 @@ static void free_strings(char **strings) * unsigned non_DFL_mask: a mask of such "special" signals * sigset_t blocked_set: current blocked signal set * - * "trap - SIGxxx": clear bit in blocked_set unless it is also in non_DFL - * "trap 'cmd' SIGxxx": set bit in blocked_set (even if 'cmd' is '') + * "trap - SIGxxx": + * clear bit in blocked_set unless it is also in non_DFL + * "trap 'cmd' SIGxxx": + * set bit in blocked_set (even if 'cmd' is '') * after [v]fork, if we plan to be a shell: - * nothing for {} subshell (say, "true | { true; true; } | true") - * unset all traps if () shell. [TODO] + * nothing for {} child shell (say, "true | { true; true; } | true") + * unset all traps if () shell. [TODO] * after [v]fork, if we plan to exec: - * POSIX says pending signal mask is cleared in child - no need to clear it. - * restore blocked signal set to one inherited by shell just prior to exec. + * POSIX says pending signal mask is cleared in child - no need to clear it. + * Restore blocked signal set to one inherited by shell just prior to exec. * * Note: as a result, we do not use signal handlers much. The only use * is to restore terminal pgrp on exit. @@ -848,7 +855,6 @@ static void init_signal_mask(void) #endif G.non_DFL_mask = mask; - /*sigemptyset(&G.blocked_set); - already is */ sigprocmask(SIG_SETMASK, NULL, &G.blocked_set); sig = 0; while (mask) { @@ -859,6 +865,7 @@ static void init_signal_mask(void) } sigprocmask(SIG_SETMASK, &G.blocked_set, &G.inherited_set); } + static void check_and_run_traps(void) { static const struct timespec zero_ts = { 0, 0 }; @@ -910,7 +917,7 @@ static void sigexit(int sig) #if ENABLE_HUSH_INTERACTIVE /* Careful: we can end up here after [v]fork. Do not restore - * tty pgrp, only top-level shell process does that */ + * tty pgrp then, only top-level shell process does that */ if (G.interactive_fd && getpid() == G.root_pid) tcsetpgrp(G.interactive_fd, G.saved_tty_pgrp); #endif @@ -931,11 +938,11 @@ static void maybe_set_sighandler(int sig) */ if (!((G.non_DFL_mask >> sig) & 1)) { handler = signal(sig, sigexit); - if (handler == SIG_IGN) /* restore back to IGN! */ + if (handler == SIG_IGN) /* oops... restore back to IGN! */ signal(sig, handler); } } -/* Used only to set handler to restore pgrp on exit, and to reset it to DFL */ +/* Used only to set handler to restore pgrp on exit */ static void set_fatal_signals_to_sigexit(void) { if (HUSH_DEBUG) { |