adjust posix_spawn dup2 action behavior to match future requirements

the resolution to Austin Group issue #411 defined new semantics for
the posix_spawn dup2 file action in the (previously useless) case
where src and dest fd are equal. future issues will require the dup2
file action to remove the close-on-exec flag. without this change,
passing fds to a child with posix_spawn while avoiding fd-leak races
in a multithreaded parent required a complex dance with temporary fds.

based on patch by Petr Skocik. changes were made to preserve the
80-column formatting of the function and to remove code that became
unreachable as a result of the new functionality.

diff --git a/src/process/posix_spawn.c b/src/process/posix_spawn.c
index 0849c71fb504b0dbf85373f93d05ebc1ae1f5a39..93fb15553537f8e3f34500f6414a5d75bdcdb85a 100644 (file)
--- a/src/process/posix_spawn.c
+++ b/src/process/posix_spawn.c
@@ -27,12 +27,7 @@ static int __sys_dup2(int old, int new)
 #ifdef SYS_dup2
        return __syscall(SYS_dup2, old, new);
 #else
-       if (old==new) {
-               int r = __syscall(SYS_fcntl, old, F_GETFD);
-               return r<0 ? r : old;
-       } else {
-               return __syscall(SYS_dup3, old, new, 0);
-       }
+       return __syscall(SYS_dup3, old, new, 0);
 #endif
 }
 
@@ -109,8 +104,17 @@ static int child(void *args_vp)
                                __syscall(SYS_close, op->fd);
                                break;
                        case FDOP_DUP2:
-                               if ((ret=__sys_dup2(op->srcfd, op->fd))<0)
-                                       goto fail;
+                               fd = op->srcfd;
+                               if (fd != op->fd) {
+                                       if ((ret=__sys_dup2(fd, op->fd))<0)
+                                               goto fail;
+                               } else {
+                                       ret = __syscall(SYS_fcntl, fd, F_GETFD);
+                                       ret = __syscall(SYS_fcntl, fd, F_SETFD,
+                                                       ret & ~FD_CLOEXEC);
+                                       if (ret<0)
+                                               goto fail;
+                               }
                                break;
                        case FDOP_OPEN:
                                fd = __sys_open(op->path, op->oflag, op->mode);