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Fix #367: add support for mdev's netlink daemon mode

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This commit replaces the `mdev -s` call to populate the device tree with
the "new" `mdev -df` daemon mode, introduced in BusyBox 1.31.0, 2019.

In daemon mode mdev listens to kernel uevents, replacing the hotplug use
of mdev.  After creating the netlink socket, 'mdev -df' performs the same
initial scan as 'mdev -s' did.

To perform device (re)discovery, module loading and setup, including any
firmware loading, a coldplug operation is typically required.  This is
done by the new /libexec/finit/coldplug script, by Alexander Zangerl.

Unlike 'mdevadm settle', mdev does not offer any mechanism to detect when
the discovery operation is done: on slower systems the triggering side,
the coldplug script, often completes quite a bit earlier than mdev's
uevent processing.  I.e., depending on <run/coldplug/success> is not an
indicator of all devices having been (re)discovered and fully set up.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
This commit is contained in:
Joachim Wiberg
2023-10-22 11:49:29 +02:00
parent f27998ae4f
commit 43d9e25ba7
6 changed files with 59 additions and 19 deletions
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system/10-hotplug.conf
-17
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@@ -1,17 +0,0 @@
# System hotplug can be handled by udev or mdev
# Either we have systemd-udevd or eudev, on the rare occasion we find
# both, we opt for the latter. Remember, you can override this by a
# custom hotplug.conf in /etc/finit.d/ or /etc/finit.d/enabled/.
service nowarn [S12345789] cgroup.system name:udevd pid:udevd log /lib/systemd/systemd-udevd -- Device event managing daemon (udev)
service nowarn [S12345789] cgroup.system name:udevd pid:udevd log udevd -D -- Device event managing daemon (udev)
# Wait for udevd to start, then wait a couple of seconds for it to become ready
run nowarn if:udevd cgroup.init :1 [S] <pid/udevd> log udevadm settle -t 0 --
run nowarn if:udevd cgroup.init :2 [S] <pid/udevd> log udevadm control --reload --
run nowarn if:udevd cgroup.init :3 [S] <pid/udevd> log udevadm trigger -c add -t devices -- Requesting device events
run nowarn if:udevd cgroup.init :4 [S] <pid/udevd> log udevadm trigger -c add -t subsystems -- Requesting subsystem events
run nowarn if:udevd cgroup.init :5 [S] <pid/udevd> log udevadm settle -t 30 -- Waiting for udev to finish
# If udevd is not available, try mdev
run nowarn conflict:udevd [S] mdev -s -- Populating device tree
system/10-hotplug.conf.in
+42
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@@ -0,0 +1,42 @@
# System hotplug handled by udev or mdev
#
# Your system usually has either udevd, mdev, or mdevd. They probe the system
# for devices, loading modules and any firmware needed. Since the bootstrap
# often needs to be synchronized carefully, we suggest using your system log
# daemon as the barrier for all other services. E.g.:
#
# service if:udevd <run/udevadm:5/success> [S0123456789] syslogd -F -- System log daemon
# service if:mdev <run/mdev/success> [S0123456789] syslogd -F -- System log daemon
#
# This provdes a <pid/syslogd> condition that can act as a barrier for all
# other services. Notice the `if:` statement and the condition for starting
# syslogd is only considered if either udevd or mdev (service) is loaded and
# is guaranteed to run after each respective run stanza have completed.
#
# Override this file by copying it to /etc/finit.d/, using the same name, then
# change the contents any way you like, it can even be empty.
# Check for systemd-udevd and eudev, if we find both, we opt for the latter.
service nowarn [S12345789] cgroup.system name:udevd pid:udevd log /lib/systemd/systemd-udevd -- Device event daemon (udev)
service nowarn [S12345789] cgroup.system name:udevd pid:udevd log udevd -D -- Device event daemon (udev)
# Wait for udevd to start, then trigger coldplug events and module loading.
# The last 'settle' call waits for it to finalize processing all uevents.
run nowarn if:udevd cgroup.init :1 [S] <pid/udevd> log udevadm settle -t 0 --
run nowarn if:udevd cgroup.init :2 [S] <pid/udevd> log udevadm control --reload --
run nowarn if:udevd cgroup.init :3 [S] <pid/udevd> log udevadm trigger -c add -t devices -- Requesting device events
run nowarn if:udevd cgroup.init :4 [S] <pid/udevd> log udevadm trigger -c add -t subsystems -- Requesting subsystem events
run nowarn if:udevd cgroup.init :5 [S] <pid/udevd> log udevadm settle -t 30 -- Waiting for udev to finish
# If udevd is not available, try mdev. The "new" daemon mode (-df) was added
# in BusyBox 1.31.0, 2019. It calls `mdev -s` internally but does not create
# a PID file when that is done, so synchronization with coldplug is fragile.
service nowarn conflict:udevd cgroup.init \
[S12345789] mdev -df -S -- Device event daemon (mdev)
# Trigger a replay of all uevents from boot, before userspace was up and the
# filesystem mounted. Compared to udevd, we don't know when 'mdev -df' has
# finished processing all events, i.e., depending on <run/coldplug/success> is
# not an indicator of all devices having been (re)discovered and fully set up.
run nowarn conflict:udevd cgroup.init name:coldplug if:<service/mdev/running> \
[S] @pkglibexecdir@/coldplug -- Cold plugging system
system/Makefile.am
+3 -1
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@@ -1,8 +1,10 @@
EXTRA_DIST = 10-hotplug.conf.in
systemdir = $(system_path)
system_DATA =
dist_system_DATA =
if BUILD_HOTPLUG_PLUGIN
dist_system_DATA += 10-hotplug.conf
system_DATA += 10-hotplug.conf
endif
if BUILD_TESTSERV_PLUGIN