systemctl: generalize GetUnitByPIDFD handling

src/systemctl/systemctl-util.c

@@ -18,6 +18,8 @@
 #include "glob-util.h"
 #include "macro.h"
 #include "path-util.h"
+#include "pidref.h"
+#include "process-util.h"
 #include "reboot-util.h"
 #include "set.h"
 #include "spawn-ask-password-agent.h"
@@ -985,3 +987,149 @@ int halt_now(enum action a) {
                 assert_not_reached();
         }
 }
+
+int get_unit_by_pid(sd_bus *bus, pid_t pid, char **ret_unit, char **ret_path) {
+        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+        _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
+        int r;
+
+        assert(bus);
+        assert(pid >= 0); /* 0 is accepted by GetUnitByPID for querying our own process. */
+
+        r = bus_call_method(bus, bus_systemd_mgr, "GetUnitByPID", &error, &reply, "u", (uint32_t) pid);
+        if (r < 0) {
+                if (sd_bus_error_has_name(&error, BUS_ERROR_NO_UNIT_FOR_PID))
+                        return log_error_errno(r, "%s", bus_error_message(&error, r));
+
+                return log_error_errno(r,
+                                       "Failed to get unit that PID " PID_FMT " belongs to: %s",
+                                       pid > 0 ? pid : getpid_cached(),
+                                       bus_error_message(&error, r));
+        }
+
+        _cleanup_free_ char *u = NULL, *p = NULL;
+        const char *path;
+
+        r = sd_bus_message_read_basic(reply, 'o', &path);
+        if (r < 0)
+                return bus_log_parse_error(r);
+
+        if (ret_unit) {
+                r = unit_name_from_dbus_path(path, &u);
+                if (r < 0)
+                        return log_error_errno(r,
+                                               "Failed to extract unit name from D-Bus object path '%s': %m",
+                                               path);
+        }
+
+        if (ret_path) {
+                p = strdup(path);
+                if (!p)
+                        return log_oom();
+        }
+
+        if (ret_unit)
+                *ret_unit = TAKE_PTR(u);
+        if (ret_path)
+                *ret_path = TAKE_PTR(p);
+
+        return 0;
+}
+
+static int get_unit_by_pidfd(sd_bus *bus, const PidRef *pid, char **ret_unit, char **ret_path) {
+        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+        _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
+        int r;
+
+        assert(bus);
+        assert(pidref_is_set(pid));
+
+        if (pid->fd < 0)
+                return -EOPNOTSUPP;
+
+        r = bus_call_method(bus, bus_systemd_mgr, "GetUnitByPIDFD", &error, &reply, "h", pid->fd);
+        if (r < 0) {
+                if (sd_bus_error_has_name(&error, SD_BUS_ERROR_UNKNOWN_METHOD))
+                        return -EOPNOTSUPP;
+
+                if (sd_bus_error_has_names(&error, BUS_ERROR_NO_UNIT_FOR_PID, BUS_ERROR_NO_SUCH_PROCESS))
+                        return log_error_errno(r, "%s", bus_error_message(&error, r));
+
+                return log_error_errno(r,
+                                       "Failed to get unit that PID " PID_FMT " belongs to: %s",
+                                       pid->pid, bus_error_message(&error, r));
+        }
+
+        _cleanup_free_ char *u = NULL, *p = NULL;
+        const char *path, *unit;
+
+        r = sd_bus_message_read(reply, "os", &path, &unit);
+        if (r < 0)
+                return bus_log_parse_error(r);
+
+        if (ret_unit) {
+                u = strdup(unit);
+                if (!u)
+                        return log_oom();
+        }
+
+        if (ret_path) {
+                p = strdup(path);
+                if (!p)
+                        return log_oom();
+        }
+
+        if (ret_unit)
+                *ret_unit = TAKE_PTR(u);
+        if (ret_path)
+                *ret_path = TAKE_PTR(p);
+
+        return 0;
+}
+
+int lookup_unit_by_pidref(sd_bus *bus, pid_t pid, char **ret_unit, char **ret_path) {
+        int r;
+
+        assert(bus);
+        assert(pid >= 0); /* 0 means our own process */
+
+        if (arg_transport != BUS_TRANSPORT_LOCAL)
+                return get_unit_by_pid(bus, pid, ret_unit, ret_path);
+
+        static bool use_pidfd = true;
+        _cleanup_(pidref_done) PidRef pidref = PIDREF_NULL;
+
+        r = pidref_set_pid(&pidref, pid);
+        if (r < 0)
+                return log_error_errno(r,
+                                       r == -ESRCH ?
+                                       "PID " PID_FMT " doesn't exist or is already gone." :
+                                       "Failed to create reference to PID " PID_FMT ": %m",
+                                       pid);
+
+        if (use_pidfd) {
+                r = get_unit_by_pidfd(bus, &pidref, ret_unit, ret_path);
+                if (r != -EOPNOTSUPP)
+                        return r;
+
+                use_pidfd = false;
+                log_debug_errno(r, "Unable to look up process using pidfd, falling back to pid.");
+        }
+
+        _cleanup_free_ char *u = NULL, *p = NULL;
+
+        r = get_unit_by_pid(bus, pidref.pid, ret_unit ? &u : NULL, ret_path ? &p : NULL);
+        if (r < 0)
+                return r;
+
+        r = pidref_verify(&pidref);
+        if (r < 0)
+                return log_error_errno(r, "Failed to verify our reference to PID " PID_FMT ": %m", pidref.pid);
+
+        if (ret_unit)
+                *ret_unit = TAKE_PTR(u);
+        if (ret_path)
+                *ret_path = TAKE_PTR(p);
+
+        return 0;
+}