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From 49bfaaa65107a9d79fbb1276e44fd4e3c98b0e9c Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Fri, 7 Feb 2014 11:58:25 +0100
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Subject: [PATCH] core: allow PIDs to be watched by two units at the same time
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In some cases it is interesting to map a PID to two units at the same
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time. For example, when a user logs in via a getty, which is reexeced to
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/sbin/login that binary will be explicitly referenced as main pid of the
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getty service, as well as implicitly referenced as part of the session
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scope.
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Conflicts:
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	src/core/manager.c
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	src/core/manager.h
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---
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 src/core/manager.c | 201 ++++++++++++++++++++++++++++++-----------------------
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 src/core/manager.h |   9 ++-
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 src/core/unit.c    |  28 ++++++--
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 3 files changed, 142 insertions(+), 96 deletions(-)
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diff --git a/src/core/manager.c b/src/core/manager.c
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index db5094f..2829c95 100644
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--- a/src/core/manager.c
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+++ b/src/core/manager.c
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@@ -525,7 +525,10 @@ int manager_new(SystemdRunningAs running_as, bool reexecuting, Manager **_m) {
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         if (!(m->jobs = hashmap_new(trivial_hash_func, trivial_compare_func)))
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                 goto fail;
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-        if (!(m->watch_pids = hashmap_new(trivial_hash_func, trivial_compare_func)))
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+        if (!(m->watch_pids1 = hashmap_new(trivial_hash_func, trivial_compare_func)))
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+                goto fail;
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+
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+        if (!(m->watch_pids2 = hashmap_new(trivial_hash_func, trivial_compare_func)))
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                 goto fail;
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         m->cgroup_unit = hashmap_new(string_hash_func, string_compare_func);
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@@ -740,7 +743,8 @@ void manager_free(Manager *m) {
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         hashmap_free(m->units);
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         hashmap_free(m->jobs);
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-        hashmap_free(m->watch_pids);
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+        hashmap_free(m->watch_pids1);
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+        hashmap_free(m->watch_pids2);
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         hashmap_free(m->watch_bus);
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         if (m->epoll_fd >= 0)
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@@ -1247,6 +1251,26 @@ unsigned manager_dispatch_dbus_queue(Manager *m) {
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         return n;
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 }
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+static void manager_invoke_notify_message(Manager *m, Unit *u, pid_t pid, char *buf, size_t n) {
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+        _cleanup_strv_free_ char **tags = NULL;
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+
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+        assert(m);
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+        assert(u);
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+        assert(buf);
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+        assert(n > 0);
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+
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+        tags = strv_split(buf, "\n\r");
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+        if (!tags) {
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+                log_oom();
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+                return;
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+        }
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+
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+        log_debug_unit(u->id, "Got notification message for unit %s", u->id);
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+
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+        if (UNIT_VTABLE(u)->notify_message)
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+                UNIT_VTABLE(u)->notify_message(u, pid, tags);
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+}
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+
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 static int manager_process_notify_fd(Manager *m) {
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         ssize_t n;
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@@ -1259,6 +1283,8 @@ static int manager_process_notify_fd(Manager *m) {
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                         .iov_len = sizeof(buf)-1,
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                 };
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+                bool found = false;
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+
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                 union {
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                         struct cmsghdr cmsghdr;
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                         uint8_t buf[CMSG_SPACE(sizeof(struct ucred))];
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@@ -1272,7 +1298,6 @@ static int manager_process_notify_fd(Manager *m) {
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                 };
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                 struct ucred *ucred;
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                 Unit *u;
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-                _cleanup_strv_free_ char **tags = NULL;
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                 n = recvmsg(m->notify_watch.fd, &msghdr, MSG_DONTWAIT);
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                 if (n <= 0) {
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@@ -1295,105 +1320,105 @@ static int manager_process_notify_fd(Manager *m) {
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                 ucred = (struct ucred*) CMSG_DATA(&control.cmsghdr);
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-                u = hashmap_get(m->watch_pids, LONG_TO_PTR(ucred->pid));
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-                if (!u) {
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-                        u = manager_get_unit_by_pid(m, ucred->pid);
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-                        if (!u) {
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-                                log_warning("Cannot find unit for notify message of PID %lu.", (unsigned long) ucred->pid);
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-                                continue;
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-                        }
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-                }
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-
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                 assert((size_t) n < sizeof(buf));
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                 buf[n] = 0;
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-                tags = strv_split(buf, "\n\r");
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-                if (!tags)
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-                        return log_oom();
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-
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-                log_debug_unit(u->id, "Got notification message for unit %s", u->id);
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-
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-                if (UNIT_VTABLE(u)->notify_message)
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-                        UNIT_VTABLE(u)->notify_message(u, ucred->pid, tags);
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-        }
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-
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-        return 0;
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-}
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-
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-static int manager_dispatch_sigchld(Manager *m) {
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-        assert(m);
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-
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-        for (;;) {
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-                siginfo_t si = {};
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-                Unit *u;
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-                int r;
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-
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-                /* First we call waitd() for a PID and do not reap the
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-                 * zombie. That way we can still access /proc/$PID for
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-                 * it while it is a zombie. */
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-                if (waitid(P_ALL, 0, &si, WEXITED|WNOHANG|WNOWAIT) < 0) {
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-
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-                        if (errno == ECHILD)
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-                                break;
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-                        if (errno == EINTR)
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-                                continue;
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-
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-                        return -errno;
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+                u = manager_get_unit_by_pid(m, ucred->pid);
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+                if (u) {
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+                        manager_invoke_notify_message(m, u, ucred->pid, buf, n);
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+                        found = true;
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                 }
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-                if (si.si_pid <= 0)
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-                        break;
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-
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-                if (si.si_code == CLD_EXITED || si.si_code == CLD_KILLED || si.si_code == CLD_DUMPED) {
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-                        _cleanup_free_ char *name = NULL;
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-
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-                        get_process_comm(si.si_pid, &name);
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-                        log_debug("Got SIGCHLD for process %lu (%s)", (unsigned long) si.si_pid, strna(name));
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+                u = hashmap_get(m->watch_pids1, LONG_TO_PTR(ucred->pid));
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+                if (u) {
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+                        manager_invoke_notify_message(m, u, ucred->pid, buf, n);
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+                        found = true;
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                 }
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-                /* Let's flush any message the dying child might still
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-                 * have queued for us. This ensures that the process
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-                 * still exists in /proc so that we can figure out
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-                 * which cgroup and hence unit it belongs to. */
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-                r = manager_process_notify_fd(m);
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-                if (r < 0)
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-                        return r;
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-
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-                /* And now figure out the unit this belongs to */
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-                u = hashmap_get(m->watch_pids, LONG_TO_PTR(si.si_pid));
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-                if (!u)
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-                        u = manager_get_unit_by_pid(m, si.si_pid);
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-
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-                /* And now, we actually reap the zombie. */
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-                if (waitid(P_PID, si.si_pid, &si, WEXITED) < 0) {
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-                        if (errno == EINTR)
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-                                continue;
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-
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-                        return -errno;
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+                u = hashmap_get(m->watch_pids2, LONG_TO_PTR(ucred->pid));
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+                if (u) {
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+                        manager_invoke_notify_message(m, u, ucred->pid, buf, n);
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+                        found = true;
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                 }
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-                if (si.si_code != CLD_EXITED && si.si_code != CLD_KILLED && si.si_code != CLD_DUMPED)
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-                        continue;
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+                if (!found)
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+                        log_warning("Cannot find unit for notify message of PID %lu.",(long unsigned) ucred->pid);
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+        }
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-                log_debug("Child %lu died (code=%s, status=%i/%s)",
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-                          (long unsigned) si.si_pid,
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-                          sigchld_code_to_string(si.si_code),
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-                          si.si_status,
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-                          strna(si.si_code == CLD_EXITED
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-                                ? exit_status_to_string(si.si_status, EXIT_STATUS_FULL)
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-                                : signal_to_string(si.si_status)));
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+        return 0;
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+}
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-                if (!u)
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-                        continue;
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+static void invoke_sigchld_event(Manager *m, Unit *u, siginfo_t *si) {
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+        assert(m);
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+        assert(u);
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+        assert(si);
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-                log_debug_unit(u->id,
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-                               "Child %lu belongs to %s", (long unsigned) si.si_pid, u->id);
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+        log_debug_unit(u->id, "Child %lu belongs to %s",(long unsigned) si->si_pid, u->id);
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-                unit_unwatch_pid(u, si.si_pid);
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-                UNIT_VTABLE(u)->sigchld_event(u, si.si_pid, si.si_code, si.si_status);
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-        }
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+        unit_unwatch_pid(u, si->si_pid);
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+        UNIT_VTABLE(u)->sigchld_event(u, si->si_pid, si->si_code, si->si_status);
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+}
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-        return 0;
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+static int manager_dispatch_sigchld(Manager *m) {
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+    assert(m);
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+
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+    for (;;) {
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+            siginfo_t si = {};
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+
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+            /* First we call waitd() for a PID and do not reap the
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+             * zombie. That way we can still access /proc/$PID for
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+             * it while it is a zombie. */
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+            if (waitid(P_ALL, 0, &si, WEXITED|WNOHANG|WNOWAIT) < 0) {
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+
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+                    if (errno == ECHILD)
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+                            break;
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+
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+                    if (errno == EINTR)
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+                            continue;
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+
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+                    return -errno;
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+            }
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+
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+            if (si.si_pid <= 0)
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+                    break;
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+
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+            if (si.si_code == CLD_EXITED || si.si_code == CLD_KILLED || si.si_code == CLD_DUMPED) {
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+                    _cleanup_free_ char *name = NULL;
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+                    Unit *u;
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+
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+                    get_process_comm(si.si_pid, &name);
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+
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+                    log_debug("Child %lu (%s) died (code=%s, status=%i/%s)",
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+                              (long unsigned) si.si_pid, strna(name),
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+                              sigchld_code_to_string(si.si_code),
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+                              si.si_status,
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+                              strna(si.si_code == CLD_EXITED
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+                                    ? exit_status_to_string(si.si_status, EXIT_STATUS_FULL)
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+                                    : signal_to_string(si.si_status)));
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+
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+                    /* And now figure out the unit this belongs
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+                     * to, it might be multiple... */
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+                    u = manager_get_unit_by_pid(m, si.si_pid);
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+                    if (u)
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+                            invoke_sigchld_event(m, u, &si);
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+                    u = hashmap_get(m->watch_pids1, LONG_TO_PTR(si.si_pid));
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+                    if (u)
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+                            invoke_sigchld_event(m, u, &si);
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+                    u = hashmap_get(m->watch_pids2, LONG_TO_PTR(si.si_pid));
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+                    if (u)
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+                            invoke_sigchld_event(m, u, &si);
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+            }
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+
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+            /* And now, we actually reap the zombie. */
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+            if (waitid(P_PID, si.si_pid, &si, WEXITED) < 0) {
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+                    if (errno == EINTR)
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+                            continue;
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+
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+                    return -errno;
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+            }
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+    }
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+
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+    return 0;
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 }
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 static int manager_start_target(Manager *m, const char *name, JobMode mode) {
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diff --git a/src/core/manager.h b/src/core/manager.h
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index ee42c5e..0133ea5 100644
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--- a/src/core/manager.h
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+++ b/src/core/manager.h
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@@ -125,7 +125,14 @@ struct Manager {
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         /* Units that should be realized */
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         LIST_HEAD(Unit, cgroup_queue);
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-        Hashmap *watch_pids;  /* pid => Unit object n:1 */
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+        /* We use two hash tables here, since the same PID might be
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+         * watched by two different units: once the unit that forked
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+         * it off, and possibly a different unit to which it was
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+         * joined as cgroup member. Since we know that it is either
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+         * one or two units for each PID we just use to hashmaps
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+         * here. */
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+        Hashmap *watch_pids1;  /* pid => Unit object n:1 */
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+        Hashmap *watch_pids2;  /* pid => Unit object n:1 */
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         char *notify_socket;
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diff --git a/src/core/unit.c b/src/core/unit.c
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index 0332094..a510eb2 100644
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--- a/src/core/unit.c
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+++ b/src/core/unit.c
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@@ -1665,16 +1665,27 @@ int unit_watch_pid(Unit *u, pid_t pid) {
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         assert(u);
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         assert(pid >= 1);
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+        /* Watch a specific PID. We only support one or two units
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+         * watching each PID for now, not more. */
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+
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+        r = hashmap_ensure_allocated(&u->manager->watch_pids1, trivial_hash_func, trivial_compare_func);
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+        if (r < 0)
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+                return r;
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+
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         r = set_ensure_allocated(&u->pids, trivial_hash_func, trivial_compare_func);
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         if (r < 0)
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                 return r;
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-        /* Watch a specific PID. We only support one unit watching
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-         * each PID for now. */
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+        r = hashmap_put(u->manager->watch_pids1, LONG_TO_PTR(pid), u);
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+        if (r == -EEXIST) {
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+                r = hashmap_ensure_allocated(&u->manager->watch_pids2, trivial_hash_func, trivial_compare_func);
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+                if (r < 0)
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+                        return r;
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-        r = set_put(u->pids, LONG_TO_PTR(pid));
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+                r = hashmap_put(u->manager->watch_pids2, LONG_TO_PTR(pid), u);
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+        }
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-        q = hashmap_put(u->manager->watch_pids, LONG_TO_PTR(pid), u);
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+        q = set_put(u->pids, LONG_TO_PTR(pid));
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         if (q < 0)
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                 return q;
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@@ -1685,7 +1696,8 @@ void unit_unwatch_pid(Unit *u, pid_t pid) {
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         assert(u);
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         assert(pid >= 1);
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-        hashmap_remove_value(u->manager->watch_pids, LONG_TO_PTR(pid), u);
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+        hashmap_remove_value(u->manager->watch_pids1, LONG_TO_PTR(pid), u);
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+        hashmap_remove_value(u->manager->watch_pids2, LONG_TO_PTR(pid), u);
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         set_remove(u->pids, LONG_TO_PTR(pid));
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 }
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@@ -1758,8 +1770,10 @@ void unit_unwatch_all_pids(Unit *u) {
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         assert(u);
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-        SET_FOREACH(e, u->pids, i)
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-                hashmap_remove_value(u->manager->watch_pids, e, u);
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+        SET_FOREACH(e, u->pids, i) {
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+                hashmap_remove_value(u->manager->watch_pids1, e, u);
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+                hashmap_remove_value(u->manager->watch_pids2, e, u);
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+        }
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         set_free(u->pids);
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         u->pids = NULL;