machined: run clone operation asynchronously in the background

Cloning an image can be slow, if the image is not on a btrfs subvolume, hence
let's make sure we do this asynchronously in a child process, so that machined
isn't blocked as long as we process the client request.

This adds a new, generic "Operation" object to machined, that is used to track
these kind of background processes.

This is inspired by the MachineOperation object that already exists to make
copy operations asynchronous. A later patch will rework the MachineOperation
logic to use the generic Operation instead.

1 files changed, 118 insertions, 0 deletions

diff --git a/src/machine/operation.c b/src/machine/operation.c
new file mode 100644
index 0000000000..53e996b48f
--- /dev/null
+++ b/src/machine/operation.c
@@ -0,0 +1,118 @@
+/***
+  This file is part of systemd.
+
+  Copyright 2016 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include "alloc-util.h"
+#include "fd-util.h"
+#include "operation.h"
+#include "process-util.h"
+
+static int operation_done(sd_event_source *s, const siginfo_t *si, void *userdata) {
+        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+        Operation *o = userdata;
+        int r;
+
+        assert(o);
+        assert(si);
+
+        log_debug("Operating " PID_FMT " is now complete with with code=%s status=%i",
+                  o->pid,
+                  sigchld_code_to_string(si->si_code), si->si_status);
+
+        o->pid = 0;
+
+        if (si->si_code != CLD_EXITED) {
+                r = sd_bus_error_setf(&error, SD_BUS_ERROR_FAILED, "Child died abnormally.");
+                goto fail;
+        }
+
+        if (si->si_status != EXIT_SUCCESS) {
+                if (read(o->errno_fd, &r, sizeof(r)) == sizeof(r))
+                        r = sd_bus_error_set_errnof(&error, r, "%m");
+                else
+                        r = sd_bus_error_setf(&error, SD_BUS_ERROR_FAILED, "Child failed.");
+
+                goto fail;
+        }
+
+        r = sd_bus_reply_method_return(o->message, NULL);
+        if (r < 0)
+                log_error_errno(r, "Failed to reply to message: %m");
+
+        operation_free(o);
+        return 0;
+
+fail:
+        r = sd_bus_reply_method_error(o->message, &error);
+        if (r < 0)
+                log_error_errno(r, "Failed to reply to message: %m");
+
+        operation_free(o);
+        return 0;
+}
+
+int operation_new(Manager *m, pid_t child, sd_bus_message *message, int errno_fd) {
+        Operation *o;
+        int r;
+
+        o = new0(Operation, 1);
+        if (!o)
+                return -ENOMEM;
+
+        r = sd_event_add_child(m->event, &o->event_source, child, WEXITED, operation_done, o);
+        if (r < 0) {
+                free(o);
+                return r;
+        }
+
+        o->pid = child;
+        o->message = sd_bus_message_ref(message);
+        o->errno_fd = errno_fd;
+
+        LIST_PREPEND(operations, m->operations, o);
+        m->n_operations++;
+        o->manager = m;
+
+        log_debug("Started new operation " PID_FMT ".", child);
+
+        /* At this point we took ownership of both the child and the errno file descriptor! */
+
+        return 0;
+}
+
+Operation *operation_free(Operation *o) {
+        if (!o)
+                return NULL;
+
+        sd_event_source_unref(o->event_source);
+
+        safe_close(o->errno_fd);
+
+        if (o->pid > 1)
+                (void) sigkill_wait(&o->pid);
+
+        sd_bus_message_unref(o->message);
+
+        if (o->manager) {
+                LIST_REMOVE(operations, o->manager->operations, o);
+                o->manager->n_operations--;
+        }
+
+        free(o);
+        return NULL;
+}