[OE-core][RFC] openssh: Start key generation in multi-user mode

["Joshua Watt" <JPEWhacker@gmail.com>]

The sshkeygen uses a lot of CPU time which delays booting (especially in
the case where no SSH connection is going to happen), but we also want
to be proactive about generating it early so that the first SSH login
doesn't have to wait a long time.

Starting the key generation when the sockets are created (which is
pretty early in the boot process) slows down the boot due to high CPU
usage, so as a compromise start it no later than multi-user mode when
things have typically settled down. Note that if an SSH connection comes
in before multi-user.target is reached, key generation will be started
immediately.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
---
 meta/recipes-connectivity/openssh/openssh/sshd.socket        | 1 -
 meta/recipes-connectivity/openssh/openssh/sshd@.service      | 1 +
 .../recipes-connectivity/openssh/openssh/sshdgenkeys.service | 5 +++++
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/meta/recipes-connectivity/openssh/openssh/sshd.socket b/meta/recipes-connectivity/openssh/openssh/sshd.socket
index 8d76d62309..12c39b26b5 100644
--- a/meta/recipes-connectivity/openssh/openssh/sshd.socket
+++ b/meta/recipes-connectivity/openssh/openssh/sshd.socket
@@ -1,6 +1,5 @@
 [Unit]
 Conflicts=sshd.service
-Wants=sshdgenkeys.service
 
 [Socket]
 ExecStartPre=@BASE_BINDIR@/mkdir -p /var/run/sshd
diff --git a/meta/recipes-connectivity/openssh/openssh/sshd@.service b/meta/recipes-connectivity/openssh/openssh/sshd@.service
index 9d9965e624..40fd38730a 100644
--- a/meta/recipes-connectivity/openssh/openssh/sshd@.service
+++ b/meta/recipes-connectivity/openssh/openssh/sshd@.service
@@ -1,5 +1,6 @@
 [Unit]
 Description=OpenSSH Per-Connection Daemon
+Wants=sshdgenkeys.service
 After=sshdgenkeys.service
 
 [Service]
diff --git a/meta/recipes-connectivity/openssh/openssh/sshdgenkeys.service b/meta/recipes-connectivity/openssh/openssh/sshdgenkeys.service
index fd81793d51..52617ec275 100644
--- a/meta/recipes-connectivity/openssh/openssh/sshdgenkeys.service
+++ b/meta/recipes-connectivity/openssh/openssh/sshdgenkeys.service
@@ -7,3 +7,8 @@ ExecStart=@LIBEXECDIR@/sshd_check_keys
 Type=oneshot
 RemainAfterExit=yes
 Nice=10
+
+[Install]
+# Start key generation no later than multi-user mode so that we can hopefully
+# have it generated before the first SSH connection
+WantedBy=multi-user.target
-- 
2.28.0