ash: use pause(), not sigsuspend(), in wait builtin

Same effect, smaller code

function                                             old     new   delta
dowait                                               463     374     -89

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 31 insertions, 26 deletions

diff --git a/shell/ash.c b/shell/ash.c
index fe112453c..fc1b5d927 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -296,8 +296,7 @@ struct globals_misc {
         volatile int suppress_int; /* counter */
         volatile /*sig_atomic_t*/ smallint pending_int; /* 1 = got SIGINT */
         volatile /*sig_atomic_t*/ smallint got_sigchld; /* 1 = got SIGCHLD */
-        /* last pending signal */
-        volatile /*sig_atomic_t*/ smallint pending_sig;
+        volatile /*sig_atomic_t*/ smallint pending_sig; /* last pending signal */
         smallint exception_type; /* kind of exception (0..5) */
         /* exceptions */
 #define EXINT 0         /* SIGINT received */
@@ -3515,11 +3514,6 @@ setsignal(int signo)
 #define CUR_RUNNING 1
 #define CUR_STOPPED 0
 
-/* mode flags for dowait */
-#define DOWAIT_NONBLOCK 0
-#define DOWAIT_BLOCK    1
-#define DOWAIT_BLOCK_OR_SIG 2
-
 #if JOBS
 /* pgrp of shell on invocation */
 static int initialpgrp; //references:2
@@ -3940,24 +3934,30 @@ sprint_status48(char *s, int status, int sigonly)
 }
 
 static int
-wait_block_or_sig(int *status, int wait_flags)
+wait_block_or_sig(int *status)
 {
-        sigset_t mask;
         int pid;
 
         do {
                 /* Poll all children for changes in their state */
                 got_sigchld = 0;
-                pid = waitpid(-1, status, wait_flags | WNOHANG);
+                /* if job control is active, accept stopped processes too */
+                pid = waitpid(-1, status, doing_jobctl ? (WNOHANG|WUNTRACED) : WNOHANG);
                 if (pid != 0)
-                        break; /* Error (e.g. EINTR) or pid */
+                        break; /* Error (e.g. EINTR, ECHILD) or pid */
 
-                /* No child is ready. Sleep until interesting signal is received */
+                /* Children exist, but none are ready. Sleep until interesting signal */
+#if 0 /* dash does this */
+                sigset_t mask;
                 sigfillset(&mask);
                 sigprocmask(SIG_SETMASK, &mask, &mask);
                 while (!got_sigchld && !pending_sig)
                         sigsuspend(&mask);
                 sigprocmask(SIG_SETMASK, &mask, NULL);
+#else
+                while (!got_sigchld && !pending_sig)
+                        pause();
+#endif
 
                 /* If it was SIGCHLD, poll children again */
         } while (got_sigchld);
@@ -3965,11 +3965,13 @@ wait_block_or_sig(int *status, int wait_flags)
         return pid;
 }
 
+#define DOWAIT_NONBLOCK 0
+#define DOWAIT_BLOCK    1
+#define DOWAIT_BLOCK_OR_SIG 2
 
 static int
 dowait(int block, struct job *job)
 {
-        int wait_flags;
         int pid;
         int status;
         struct job *jp;
@@ -3977,13 +3979,6 @@ dowait(int block, struct job *job)
 
         TRACE(("dowait(0x%x) called\n", block));
 
-        wait_flags = 0;
-        if (block == DOWAIT_NONBLOCK)
-                wait_flags = WNOHANG;
-        /* If job control is compiled in, we accept stopped processes too. */
-        if (doing_jobctl)
-                wait_flags |= WUNTRACED;
-
         /* It's wrong to call waitpid() outside of INT_OFF region:
          * signal can arrive just after syscall return and handler can
          * longjmp away, losing stop/exit notification processing.
@@ -3994,17 +3989,27 @@ dowait(int block, struct job *job)
          * in INT_OFF region: "wait" needs to wait for any running job
          * to change state, but should exit on any trap too.
          * In INT_OFF region, a signal just before syscall entry can set
-         * pending_sig valiables, but we can't check them, and we would
+         * pending_sig variables, but we can't check them, and we would
          * either enter a sleeping waitpid() (BUG), or need to busy-loop.
+         *
          * Because of this, we run inside INT_OFF, but use a special routine
-         * which combines waitpid() and sigsuspend().
+         * which combines waitpid() and pause().
+         * This is the reason why we need to have a handler for SIGCHLD:
+         * SIG_DFL handler does not wake pause().
          */
         INT_OFF;
-        if (block == DOWAIT_BLOCK_OR_SIG)
-                pid = wait_block_or_sig(&status, wait_flags);
-        else
-                /* NB: _not_ safe_waitpid, we need to detect EINTR. */
+        if (block == DOWAIT_BLOCK_OR_SIG) {
+                pid = wait_block_or_sig(&status);
+        } else {
+                int wait_flags = 0;
+                if (block == DOWAIT_NONBLOCK)
+                        wait_flags = WNOHANG;
+                /* if job control is active, accept stopped processes too */
+                if (doing_jobctl)
+                        wait_flags |= WUNTRACED;
+                /* NB: _not_ safe_waitpid, we need to detect EINTR */
                 pid = waitpid(-1, &status, wait_flags);
+        }
         TRACE(("wait returns pid=%d, status=0x%x, errno=%d(%s)\n",
                                 pid, status, errno, strerror(errno)));
         if (pid <= 0)