Lennart Poettering
d8fdc62037
dbus-daemon currently uses a backlog of 30 on its D-bus system bus socket. On overloaded systems this means that only 30 connections may be queued without dbus-daemon processing them before further connection attempts fail. Our cgroups-agent binary so far used D-Bus for its messaging, and hitting this limit hence may result in us losing cgroup empty messages. This patch adds a seperate cgroup agent socket of type AF_UNIX/SOCK_DGRAM. Since sockets of these types need no connection set up, no listen() backlog applies. Our cgroup-agent binary will hence simply block as long as it can't enqueue its datagram message, so that we won't lose cgroup empty messages as likely anymore. This also rearranges the ordering of the processing of SIGCHLD signals, service notification messages (sd_notify()...) and the two types of cgroup notifications (inotify for the unified hierarchy support, and agent for the classic hierarchy support). We now always process events for these in the following order: 1. service notification messages (SD_EVENT_PRIORITY_NORMAL-7) 2. SIGCHLD signals (SD_EVENT_PRIORITY_NORMAL-6) 3. cgroup inotify and cgroup agent (SD_EVENT_PRIORITY_NORMAL-5) This is because when receiving SIGCHLD we invalidate PID information, which we need to process the service notification messages which are bound to PIDs. Hence the order between the first two items. And we want to process SIGCHLD metadata to detect whether a service is gone, before using cgroup notifications, to decide when a service is gone, since the former carries more useful metadata. Related to this: https://bugs.freedesktop.org/show_bug.cgi?id=95264 https://github.com/systemd/systemd/issues/1961
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