dbus: rauc: update_channels: add a concept of a single primary channel

RAUC native update polling only supports a single update channel,
while our native update polling did support multiple
(all channels which RAUC would have accepted updates from,
based on the enabled signing certificates, were polled for updates and the
user was asked if they wanted to install updates from them).

Prepare for the change by adding a concept of a single primary update
channel. The primary channel is the first enabled one. Based on the
channel definition file name.

E.g. on production TACs these channel files are available:

    root@lxatac-00011:~# ls /usr/share/tacd/update_channels/
    01_stable.yaml 05_testing.yaml

They are sorted by name when they are read from disk, so if both
`stable.cert.pem` and `testing.cert.pem` are found
in `/etc/rauc/certificates-enabled/`, then the stable channel will be
the primary channel, but bundles from the testing channel may still be
installed via the command line interface (e.g. to facilitate a channel
switch).

Signed-off-by: Leonard Göhrs <[email protected]>

Author: hnez

openapi.yaml

@@ -1132,6 +1132,8 @@ components:
                 type: integer
           enabled:
             type: boolean
+          primary:
+            type: boolean
           bundle:
             type: object
             properties:

src/dbus/rauc/update_channels.rs

@@ -48,6 +48,7 @@ pub struct Channel {
     pub url: String,
     pub polling_interval: Option<Duration>,
     pub enabled: bool,
+    pub primary: bool,
     pub bundle: Option<UpstreamBundle>,
 }
 
@@ -110,6 +111,7 @@ impl Channel {
             url: channel_file.url.trim().to_string(),
             polling_interval,
             enabled: false,
+            primary: false,
             bundle: None,
         };
 
@@ -147,13 +149,21 @@ impl Channels {
 
         let mut channels: Vec<Channel> = Vec::new();
 
+        let mut have_primary = false;
+
         for dir_entry in dir_entries {
-            let channel = Channel::from_file(&dir_entry.path())?;
+            let mut channel = Channel::from_file(&dir_entry.path())?;
 
             if channels.iter().any(|ch| ch.name == channel.name) {
                 bail!("Encountered duplicate channel name \"{}\"", channel.name);
             }
 
+            // There can only be one primary channel.
+            // If multiple channels are enabled the primary one is the one with
+            // the highest precedence.
+            channel.primary = channel.enabled && !have_primary;
+            have_primary |= channel.primary;
+
             channels.push(channel);
         }