machined: when opening a shell via machined, pass tty fds in

With this change we'll open the shell's tty right from machined and then
pass it to the transient unit we create. This way we make sure the pty
is opened exactly as long as the transient service is around, and no
longer, and vice versa. This way pty forwarders do not have to deal with
EIO problems due to vhangup, as the pty is open all the time from the
point we set things up to the point where the service goes away.

2 files changed, 49 insertions, 0 deletions

diff --git a/src/basic/terminal-util.c b/src/basic/terminal-util.c
index 50a86a331c..e9097d8ae5 100644
--- a/src/basic/terminal-util.c
+++ b/src/basic/terminal-util.c
@@ -1152,3 +1152,51 @@ int openpt_in_namespace(pid_t pid, int flags) {
 
         return receive_one_fd(pair[0], 0);
 }
+
+int open_terminal_in_namespace(pid_t pid, const char *name, int mode) {
+        _cleanup_close_ int pidnsfd = -1, mntnsfd = -1, usernsfd = -1, rootfd = -1;
+        _cleanup_close_pair_ int pair[2] = { -1, -1 };
+        siginfo_t si;
+        pid_t child;
+        int r;
+
+        r = namespace_open(pid, &pidnsfd, &mntnsfd, NULL, &usernsfd, &rootfd);
+        if (r < 0)
+                return r;
+
+        if (socketpair(AF_UNIX, SOCK_DGRAM, 0, pair) < 0)
+                return -errno;
+
+        child = fork();
+        if (child < 0)
+                return -errno;
+
+        if (child == 0) {
+                int master;
+
+                pair[0] = safe_close(pair[0]);
+
+                r = namespace_enter(pidnsfd, mntnsfd, -1, usernsfd, rootfd);
+                if (r < 0)
+                        _exit(EXIT_FAILURE);
+
+                master = open_terminal(name, mode|O_NOCTTY|O_CLOEXEC);
+                if (master < 0)
+                        _exit(EXIT_FAILURE);
+
+                if (send_one_fd(pair[1], master, 0) < 0)
+                        _exit(EXIT_FAILURE);
+
+                _exit(EXIT_SUCCESS);
+        }
+
+        pair[1] = safe_close(pair[1]);
+
+        r = wait_for_terminate(child, &si);
+        if (r < 0)
+                return r;
+        if (si.si_code != CLD_EXITED || si.si_status != EXIT_SUCCESS)
+                return -EIO;
+
+        return receive_one_fd(pair[0], 0);
+}
diff --git a/src/basic/terminal-util.h b/src/basic/terminal-util.h
index 050d0524a5..ee0b68b433 100644
--- a/src/basic/terminal-util.h
+++ b/src/basic/terminal-util.h
@@ -124,3 +124,4 @@ int ptsname_malloc(int fd, char **ret);
 int ptsname_namespace(int pty, char **ret);
 
 int openpt_in_namespace(pid_t pid, int flags);
+int open_terminal_in_namespace(pid_t pid, const char *name, int mode);