activate: add a new switch --inetd to enable inetd-style socket activation

Previously, using --accept would enable inetd-style socket activation in addition to per-connection operation. This is
now split into two switches: --accept only switches between per-connection or single-instance operation. --inetd
switches between inetd-style or new-style fd passing.

This breaks the interface of the tool, but given that it is a debugging tool shipped in /usr/lib/systemd/ it's not
really a public interface.

This change allows testing new-style per-connection daemons.

2 files changed, 103 insertions, 79 deletions

diff --git a/man/systemd-activate.xml b/man/systemd-activate.xml
index 61a2bc8608..995e6eecce 100644
--- a/man/systemd-activate.xml
+++ b/man/systemd-activate.xml
@@ -60,27 +60,21 @@
   <refsect1>
     <title>Description</title>
 
-    <para><command>systemd-activate</command> can be used to
-    launch a socket-activated daemon from the command line for
-    testing purposes. It can also be used to launch single instances
-    of the daemon per connection (inetd-style).
+    <para><command>systemd-activate</command> may be used to launch a socket-activated service binary from the command
+    line for testing purposes. It may also be used to launch individual instances of the service binary per connection.
     </para>
 
     <para>The daemon to launch and its options should be specified
     after options intended for <command>systemd-activate</command>.
     </para>
 
-    <para>If the <option>-a</option> option is given, file descriptor
-    of the connection will be used as the standard input and output of
-    the launched process. Otherwise, standard input and output will be
-    inherited, and sockets will be passed through file descriptors 3
-    and higher. Sockets passed through <varname>$LISTEN_FDS</varname>
-    to <command>systemd-activate</command> will be passed through to
-    the daemon, in the original positions. Other sockets specified
-    with <option>--listen</option> will use consecutive descriptors.
-    By default, <command>systemd-activate</command> listens on a
-    stream socket, use <option>--datagram</option> to listen on
-    a datagram socket instead (see below).
+    <para>If the <option>--inetd</option> option is given, the socket file descriptor will be used as the standard
+    input and output of the launched process. Otherwise, standard input and output will be inherited, and sockets will
+    be passed through file descriptors 3 and higher. Sockets passed through <varname>$LISTEN_FDS</varname> to
+    <command>systemd-activate</command> will be passed through to the daemon, in the original positions. Other sockets
+    specified with <option>--listen=</option> will use consecutive descriptors.  By default,
+    <command>systemd-activate</command> listens on a stream socket, use <option>--datagram</option> and
+    <option>--seqpacket</option> to listen on datagram or sequential packet sockets instead (see below).
     </para>
   </refsect1>
 
@@ -101,9 +95,8 @@
         <term><option>-a</option></term>
         <term><option>--accept</option></term>
 
-        <listitem><para>Launch a separate instance of daemon per
-        connection and pass the connection socket as standard input
-        and standard output.</para></listitem>
+        <listitem><para>Launch an instance of the service binary for each connection and pass the connection
+        socket.</para></listitem>
       </varlistentry>
 
       <varlistentry>
@@ -123,6 +116,14 @@
       </varlistentry>
 
       <varlistentry>
+        <term><option>--inetd</option></term>
+
+        <listitem><para>Use the inetd protocol for passing file descriptors, i.e. as standard input and standard
+        output, instead of the new-style protocol for passing file descriptors using <varname>$LISTEN_FDS</varname>
+        (see above).</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
         <term><option>-E <replaceable>VAR</replaceable><optional>=<replaceable>VALUE</replaceable></optional></option></term>
         <term><option>--setenv=<replaceable>VAR</replaceable><optional>=<replaceable>VALUE</replaceable></optional></option></term>
 
@@ -179,7 +180,7 @@
     <example>
       <title>Run an echo server on port 2000</title>
 
-      <programlisting>$ /usr/lib/systemd/systemd-activate -l 2000 -a cat</programlisting>
+      <programlisting>$ /usr/lib/systemd/systemd-activate -l 2000 --inetd -a cat</programlisting>
     </example>
 
     <example>
diff --git a/src/activate/activate.c b/src/activate/activate.c
index 559ce33d89..0db4967edb 100644
--- a/src/activate/activate.c
+++ b/src/activate/activate.c
@@ -41,6 +41,7 @@ static int arg_socket_type = SOCK_STREAM;
 static char** arg_args = NULL;
 static char** arg_setenv = NULL;
 static const char *arg_fdname = NULL;
+static bool arg_inetd = false;
 
 static int add_epoll(int epoll_fd, int fd) {
         struct epoll_event ev = {
@@ -127,14 +128,20 @@ static int open_sockets(int *epoll_fd, bool accept) {
         return count;
 }
 
-static int launch(char* name, char **argv, char **env, int fds) {
+static int exec_process(const char* name, char **argv, char **env, int start_fd, int n_fds) {
 
-        static const char* tocopy[] = {"TERM=", "PATH=", "USER=", "HOME="};
         _cleanup_strv_free_ char **envp = NULL;
-        _cleanup_free_ char *tmp = NULL;
+        _cleanup_free_ char *joined = NULL;
         unsigned n_env = 0, length;
-        char **s;
+        const char *tocopy;
         unsigned i;
+        char **s;
+        int r;
+
+        if (arg_inetd && n_fds != 1) {
+                log_error("--inetd only supported for single file descriptors.");
+                return -EINVAL;
+        }
 
         length = strv_length(arg_setenv);
 
@@ -144,6 +151,7 @@ static int launch(char* name, char **argv, char **env, int fds) {
                 return log_oom();
 
         STRV_FOREACH(s, arg_setenv) {
+
                 if (strchr(*s, '=')) {
                         char *k;
 
@@ -167,13 +175,15 @@ static int launch(char* name, char **argv, char **env, int fds) {
                         envp[n_env] = strdup(n);
                         if (!envp[n_env])
                                 return log_oom();
+
+                        n_env ++;
                 }
         }
 
-        for (i = 0; i < ELEMENTSOF(tocopy); i++) {
+        FOREACH_STRING(tocopy, "TERM=", "PATH=", "USER=", "HOME=") {
                 const char *n;
 
-                n = strv_find_prefix(env, tocopy[i]);
+                n = strv_find_prefix(env, tocopy);
                 if (!n)
                         continue;
 
@@ -184,50 +194,76 @@ static int launch(char* name, char **argv, char **env, int fds) {
                 n_env ++;
         }
 
-        if ((asprintf((char**)(envp + n_env++), "LISTEN_FDS=%d", fds) < 0) ||
-            (asprintf((char**)(envp + n_env++), "LISTEN_PID=%d", getpid()) < 0))
-                return log_oom();
+        if (arg_inetd) {
+                assert(n_fds == 1);
 
-        if (arg_fdname) {
-                char *e;
+                r = dup2(start_fd, STDIN_FILENO);
+                if (r < 0)
+                        return log_error_errno(errno, "Failed to dup connection to stdin: %m");
 
-                e = strappend("LISTEN_FDNAMES=", arg_fdname);
-                if (!e)
+                r = dup2(start_fd, STDOUT_FILENO);
+                if (r < 0)
+                        return log_error_errno(errno, "Failed to dup connection to stdout: %m");
+
+                start_fd = safe_close(start_fd);
+        } else {
+                if (start_fd != SD_LISTEN_FDS_START) {
+                        assert(n_fds == 1);
+
+                        r = dup2(start_fd, SD_LISTEN_FDS_START);
+                        if (r < 0)
+                                return log_error_errno(errno, "Failed to dup connection: %m");
+
+                        safe_close(start_fd);
+                        start_fd = SD_LISTEN_FDS_START;
+                }
+
+                if (asprintf((char**)(envp + n_env++), "LISTEN_FDS=%i", n_fds) < 0)
                         return log_oom();
 
-                for (i = 1; i < (unsigned) fds; i++) {
-                        char *c;
+                if (asprintf((char**)(envp + n_env++), "LISTEN_PID=" PID_FMT, getpid()) < 0)
+                        return log_oom();
 
-                        c = strjoin(e, ":", arg_fdname, NULL);
-                        if (!c) {
-                                free(e);
+                if (arg_fdname) {
+                        char *e;
+
+                        e = strappend("LISTEN_FDNAMES=", arg_fdname);
+                        if (!e)
                                 return log_oom();
+
+                        for (i = 1; i < (unsigned) n_fds; i++) {
+                                char *c;
+
+                                c = strjoin(e, ":", arg_fdname, NULL);
+                                if (!c) {
+                                        free(e);
+                                        return log_oom();
+                                }
+
+                                free(e);
+                                e = c;
                         }
 
-                        free(e);
-                        e = c;
+                        envp[n_env++] = e;
                 }
-
-                envp[n_env++] = e;
         }
 
-        tmp = strv_join(argv, " ");
-        if (!tmp)
+        joined = strv_join(argv, " ");
+        if (!joined)
                 return log_oom();
 
-        log_info("Execing %s (%s)", name, tmp);
+        log_info("Execing %s (%s)", name, joined);
         execvpe(name, argv, envp);
 
-        return log_error_errno(errno, "Failed to execp %s (%s): %m", name, tmp);
+        return log_error_errno(errno, "Failed to execp %s (%s): %m", name, joined);
 }
 
-static int launch1(const char* child, char** argv, char **env, int fd) {
-        _cleanup_free_ char *tmp = NULL;
+static int fork_and_exec_process(const char* child, char** argv, char **env, int fd) {
+        _cleanup_free_ char *joined = NULL;
         pid_t parent_pid, child_pid;
-        int r;
 
-        tmp = strv_join(argv, " ");
-        if (!tmp)
+        joined = strv_join(argv, " ");
+        if (!joined)
                 return log_oom();
 
         parent_pid = getpid();
@@ -242,24 +278,6 @@ static int launch1(const char* child, char** argv, char **env, int fd) {
                 (void) reset_all_signal_handlers();
                 (void) reset_signal_mask();
 
-                r = dup2(fd, STDIN_FILENO);
-                if (r < 0) {
-                        log_error_errno(errno, "Failed to dup connection to stdin: %m");
-                        _exit(EXIT_FAILURE);
-                }
-
-                r = dup2(fd, STDOUT_FILENO);
-                if (r < 0) {
-                        log_error_errno(errno, "Failed to dup connection to stdout: %m");
-                        _exit(EXIT_FAILURE);
-                }
-
-                r = close(fd);
-                if (r < 0) {
-                        log_error_errno(errno, "Failed to close dupped connection: %m");
-                        _exit(EXIT_FAILURE);
-                }
-
                 /* Make sure the child goes away when the parent dies */
                 if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0)
                         _exit(EXIT_FAILURE);
@@ -269,29 +287,27 @@ static int launch1(const char* child, char** argv, char **env, int fd) {
                 if (getppid() != parent_pid)
                         _exit(EXIT_SUCCESS);
 
-                execvp(child, argv);
-                log_error_errno(errno, "Failed to exec child %s: %m", child);
+                exec_process(child, argv, env, fd, 1);
                 _exit(EXIT_FAILURE);
         }
 
-        log_info("Spawned %s (%s) as PID %d", child, tmp, child_pid);
-
+        log_info("Spawned %s (%s) as PID %d", child, joined, child_pid);
         return 0;
 }
 
 static int do_accept(const char* name, char **argv, char **envp, int fd) {
         _cleanup_free_ char *local = NULL, *peer = NULL;
-        _cleanup_close_ int fd2 = -1;
+        _cleanup_close_ int fd_accepted = -1;
 
-        fd2 = accept4(fd, NULL, NULL, 0);
-        if (fd2 < 0)
+        fd_accepted = accept4(fd, NULL, NULL, 0);
+        if (fd_accepted < 0)
                 return log_error_errno(errno, "Failed to accept connection on fd:%d: %m", fd);
 
-        getsockname_pretty(fd2, &local);
-        getpeername_pretty(fd2, true, &peer);
+        getsockname_pretty(fd_accepted, &local);
+        getpeername_pretty(fd_accepted, true, &peer);
         log_info("Connection from %s to %s", strna(peer), strna(local));
 
-        return launch1(name, argv, envp, fd2);
+        return fork_and_exec_process(name, argv, envp, fd_accepted);
 }
 
 /* SIGCHLD handler. */
@@ -330,6 +346,7 @@ static void help(void) {
                "     --seqpacket           Listen on SOCK_SEQPACKET instead of stream socket\n"
                "  -a --accept              Spawn separate child for each connection\n"
                "  -E --setenv=NAME[=VALUE] Pass an environment variable to children\n"
+               "     --inetd               Enable inetd file descriptor passing protocol\n"
                "\n"
                "Note: file descriptors from sd_listen_fds() will be passed through.\n"
                , program_invocation_short_name);
@@ -340,6 +357,7 @@ static int parse_argv(int argc, char *argv[]) {
                 ARG_VERSION = 0x100,
                 ARG_FDNAME,
                 ARG_SEQPACKET,
+                ARG_INETD,
         };
 
         static const struct option options[] = {
@@ -352,6 +370,7 @@ static int parse_argv(int argc, char *argv[]) {
                 { "setenv",      required_argument, NULL, 'E'           },
                 { "environment", required_argument, NULL, 'E'           }, /* legacy alias */
                 { "fdname",      required_argument, NULL, ARG_FDNAME    },
+                { "inetd",       no_argument,       NULL, ARG_INETD     },
                 {}
         };
 
@@ -414,6 +433,10 @@ static int parse_argv(int argc, char *argv[]) {
                         arg_fdname = optarg;
                         break;
 
+                case ARG_INETD:
+                        arg_inetd = true;
+                        break;
+
                 case '?':
                         return -EINVAL;
 
@@ -482,7 +505,7 @@ int main(int argc, char **argv, char **envp) {
                         break;
         }
 
-        launch(argv[optind], argv + optind, envp, n);
+        exec_process(argv[optind], argv + optind, envp, SD_LISTEN_FDS_START, n);
 
         return EXIT_SUCCESS;
 }