mail: deobfuscate launch_helper()

13 bytes are not worth the risk of doing something iffy after vfork().
Let's have much clearer code there.

function                                             old     new   delta
launch_helper                                        175     188     +13

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

1 files changed, 27 insertions, 29 deletions

diff --git a/mailutils/mail.c b/mailutils/mail.c
index 9735d48f6..7e9efdbfa 100644
--- a/mailutils/mail.c
+++ b/mailutils/mail.c
@@ -10,35 +10,35 @@
 #include "libbb.h"
 #include "mail.h"
 
-// generic signal handler
+// common signal handler
 static void signal_handler(int signo)
 {
-#define err signo
         if (SIGALRM == signo) {
                 bb_simple_error_msg_and_die("timed out");
         }
 
-        // SIGCHLD. reap zombies
-        if (safe_waitpid(G.helper_pid, &err, WNOHANG) > 0) {
-                if (WIFSIGNALED(err))
-                        bb_error_msg_and_die("helper killed by signal %u", WTERMSIG(err));
-                if (WIFEXITED(err)) {
-                        G.helper_pid = 0;
-                        if (WEXITSTATUS(err))
-                                bb_error_msg_and_die("helper exited (%u)", WEXITSTATUS(err));
-                }
+        // SIGCHLD. reap the zombie if we expect one
+        if (G.helper_pid == 0)
+                return;
+#define status signo
+        if (safe_waitpid(G.helper_pid, &status, WNOHANG) > 0) {
+                G.helper_pid = 0;
+                if (WIFSIGNALED(status))
+                        bb_error_msg_and_die("helper killed by signal %u", WTERMSIG(status));
+                if (WIFEXITED(status) && WEXITSTATUS(status) != 0)
+                        bb_error_msg_and_die("helper exited (%u)", WEXITSTATUS(status));
         }
-#undef err
+#undef status
 }
 
 void FAST_FUNC launch_helper(const char **argv)
 {
-        // setup vanilla unidirectional pipes interchange
-        int i;
-        int pipes[4];
+        pid_t pid;
+        struct fd_pair child_out;
+        struct fd_pair child_in;
 
-        xpipe(pipes);
-        xpipe(pipes + 2);
+        xpiped_pair(child_out);
+        xpiped_pair(child_in);
 
         // NB: handler must be installed before vfork
         bb_signals(0
@@ -46,25 +46,23 @@ void FAST_FUNC launch_helper(const char **argv)
                 + (1 << SIGALRM)
                 , signal_handler);
 
-        G.helper_pid = xvfork();
-
-        i = (!G.helper_pid) * 2; // for parent:0, for child:2
-        close(pipes[i + 1]);     // 1 or 3 - closing one write end
-        close(pipes[2 - i]);     // 2 or 0 - closing one read end
-        xmove_fd(pipes[i], STDIN_FILENO);      // 0 or 2 - using other read end
-        xmove_fd(pipes[3 - i], STDOUT_FILENO); // 3 or 1 - using other write end
-        // End result:
-        // parent stdout [3] -> child stdin [2]
-        // child stdout [1] -> parent stdin [0]
-
-        if (!G.helper_pid) {
+        G.helper_pid = pid = xvfork();
+        if (pid == 0) {
                 // child
+                close(child_in.wr);
+                close(child_out.rd);
+                xmove_fd(child_in.rd, STDIN_FILENO);
+                xmove_fd(child_out.wr, STDOUT_FILENO);
                 // if parent dies, get SIGTERM
                 prctl(PR_SET_PDEATHSIG, SIGTERM, 0, 0, 0);
                 // try to execute connection helper
                 // NB: SIGCHLD & SIGALRM revert to SIG_DFL on exec
                 BB_EXECVP_or_die((char**)argv);
         }
+        close(child_out.wr);
+        close(child_in.rd);
+        xmove_fd(child_out.rd, STDIN_FILENO);
+        xmove_fd(child_in.wr, STDOUT_FILENO);
 
         // parent goes on
 }