[pve-devel] [PATCH common v4 1/2] systemd: add notify() helper

[Fiona Ebner]

Add a pure Perl reimplementation of systemd's sd_notify() mechanism as
defined in systemd/sd-daemon.h based on the example implementations in
'man 3 sd_notify'.

The initial user of this helper is intended to be the pve-dbus-vmstate
service, so it can notify startup completion only once the
dbus-vmstate QEMU object is ready to be used.

EAGAIN is not checked for, because it does not occur for blocking
Unix domain sockets, see 'man 2 send'. The socket is a datagram
socket and a single datagram will be sent. If not all data can be
written, error out like the example code in 'man 3 sd_notify'.

Co-developed-by: Thomas Lamprecht <t.lamprecht at proxmox.com>
Co-developed-by: Wolfgang Bumiller <w.bumiller at proxmox.com>
Signed-off-by: Fiona Ebner <f.ebner at proxmox.com>
---

Changes in v4:
* Also handle abstract socket path.
* Only resend upon EINTR, otherwise the datagram should be sent in one
  go.
* Drop unnecessary flush.
* Drop $unset_environment argument.
* Rename to just PVE::Systemd::notify() to make it clear that it's not
  the exact same as sd_notify().
* Use POD for documentation.
* Return early if there is no socket path.
* Die if there is no message.
* Check that socket path starts with '/' or '@'.

 src/PVE/Systemd.pm | 49 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/src/PVE/Systemd.pm b/src/PVE/Systemd.pm
index e6d6f88..8fc06a5 100644
--- a/src/PVE/Systemd.pm
+++ b/src/PVE/Systemd.pm
@@ -3,9 +3,12 @@ package PVE::Systemd;
 use strict;
 use warnings;
 
+use IO::Socket::UNIX;
 use Net::DBus qw(dbus_uint32 dbus_uint64 dbus_boolean);
 use Net::DBus::Callback;
 use Net::DBus::Reactor;
+use POSIX qw(EINTR);
+use Socket qw(SOCK_DGRAM);
 
 use PVE::Tools qw(file_set_contents file_get_contents trim);
 
@@ -282,4 +285,50 @@ sub write_ini {
     file_set_contents($filename, $content);
 }
 
+=head3 notify()
+
+This is a pure Perl reimplementation of systemd's C<sd_notify()> mechanism as defined in
+C<systemd/sd-daemon.h>, based on the example implementations in C<man 3 sd_notify>. Does not return
+a value, but dies upon error.
+
+=cut
+
+sub notify {
+    my ($message) = @_;
+
+    # nothing to do if there is no socket
+    my $socket_path = $ENV{NOTIFY_SOCKET} or return;
+
+    die "notify systemd invalid socket path '$socket_path'\n" if $socket_path !~ m|^[/@]|;
+    die "notify systemd called without a message\n" if !$message;
+
+    # might be an abstract socket
+    $socket_path =~ s/^@/\0/;
+
+    my $socket = IO::Socket::UNIX->new(
+        Type => SOCK_DGRAM(),
+        Peer => $socket_path,
+    ) or die "notify systemd: unable to connect to socket $socket_path - $IO::Socket::errstr\n";
+
+    # we won't be reading from the socket
+    $socket->shutdown(SHUT_RD);
+
+    my $res;
+    while (1) {
+        $res = $socket->send($message);
+        if ($res) {
+            die "notify systemd: protocol error writing to socket '$socket_path'\n"
+                if $res < length($message);
+            last;
+        } else {
+            next if $! == EINTR;
+            die "notify systemd: sending to '$socket_path' failed - $!\n";
+        }
+    }
+
+    close($socket);
+
+    return;
+}
+
 1;
-- 
2.47.3