ZED: add support for desktop notifications

This commit adds support for desktop notifications via the
freedesktop.org Notifications D-Bus interface
<https://specifications.freedesktop.org/notification-spec/latest/>. This
enables immediate graphical notification of ZFS events to users who run
ZFS on traditional desktop environments like KDE and GNOME. The content
of the notifications is the same as what would be currently delivered by
other methods such as email, ntfy, etc.

Signed-off-by: xenia <[email protected]>

cmd/zed/zed.d/zed-functions.sh

@@ -213,6 +213,10 @@ zed_notify()
     [ "${rv}" -eq 0 ] && num_success=$((num_success + 1))
     [ "${rv}" -eq 1 ] && num_failure=$((num_failure + 1))
 
+    zed_notify_dbus "${subject}" "${pathname}"; rv=$?
+    [ "${rv}" -eq 0 ] && num_success=$((num_success + 1))
+    [ "${rv}" -eq 1 ] && num_failure=$((num_failure + 1))
+
     [ "${num_success}" -gt 0 ] && return 0
     [ "${num_failure}" -gt 0 ] && return 1
     return 2
@@ -719,6 +723,89 @@ zed_notify_gotify()
 }
 
 
+# zed_notify_dbus (subject, pathname)
+#
+# Send a desktop notification via D-Bus.
+# The variable (ZED_USE_DBUS) defines whether to use D-Bus to send desktop
+# notifications.
+#
+# Requires systemd (busctl) executables to be installed in the standard PATH.
+#
+# References
+#   https://specifications.freedesktop.org/notification-spec/latest/
+#   https://www.freedesktop.org/software/systemd/man/latest/busctl.html
+#
+# Arguments
+#   subject: notification subject
+#   pathname: pathname containing the notification message (OPTIONAL)
+#
+# Globals
+#   ZED_USE_DBUS
+#
+# Return
+#   0: notification sent
+#   1: notification failed
+#   2: not configured
+#
+zed_notify_dbus()
+{
+    local subject="$1"
+    local pathname="${2:-"/dev/null"}"
+    local msg_body
+    local msg_out
+    local msg_err
+    local exit_status=0
+    local dir
+    local userid
+
+    [ -n "${ZED_USE_DBUS}" ] || return 2
+
+    if [ ! -r "${pathname}" ]; then
+        zed_log_err "dbus cannot read \"${pathname}\""
+        return 1
+    fi
+
+    zed_check_cmd "busctl" || return 1
+
+    # Read the message body in.
+    #
+    msg_body="$(cat "${pathname}")"
+
+    if [ -z "${msg_body}" ]
+    then
+        msg_body=$subject
+        subject=""
+    fi
+
+    # Send the notification to all users with a dbus session and check for
+    # errors.
+    # We use busctl(1) manually rather than eg notify-send(1) due to its
+    # ability to send D-Bus messages from root to a non-root user with the
+    # "--machine=<user>@.host" flag.
+    for dir in /run/user/*; do
+        if [ -S "$dir/bus" ]; then
+            userid="$(basename "$dir")"
+            msg_out="$( \
+                busctl --user --machine "$userid@.host" -- \
+                    call org.freedesktop.Notifications \
+                    /org/freedesktop/Notifications \
+                    org.freedesktop.Notifications Notify \
+                    "susssasa{sv}i" \
+                    "ZFS" 0 "drive-harddisk-symbolic" \
+                    "$subject" "$msg_body"
+                    0 2 urgency y 2 sender-pid x "$$" "-1" \
+                2>/dev/null
+            )"; rv=$?
+
+            if [ "${rv}" -ne 0 ]; then
+                zed_log_err "busctl exit=${rv}"
+                exit_status=1
+            fi
+        fi
+    done
+    return "$exit_status"
+}
+
 
 # zed_rate_limit (tag, [interval])
 #

cmd/zed/zed.d/zed.rc

@@ -197,3 +197,10 @@ ZED_SYSLOG_SUBCLASS_EXCLUDE="history_event"
 # Gotify application associated with ZED_GOTIFY_APPTOKEN.
 # Value is an integer 0 and up.
 #ZED_GOTIFY_PRIORITY=""
+
+##
+# Whether to send desktop notifications via D-Bus
+# If defined, busctl(1) will be used to send desktop notifications via
+# the org.freedesktop.Notifications D-Bus interface
+# Disabled by default; uncomment to enable.
+#ZED_USE_DBUS=1