net: netconsole: Populate dynamic entry even if netpoll fails

Currently, netconsole discards targets that fail during initialization,
causing two issues:

1) Inconsistency between target list and configfs entries
  * user pass cmdline0, cmdline1. If cmdline0 fails, then cmdline1
    becomes cmdline0 in configfs.

2) Inability to manage failed targets from userspace
  * If user pass a target that fails with netpoll (interface not loaded at
    netcons initialization time, such as interface is a module), then
    the target will not exist in the configfs, so, user cannot re-enable
    or modify it from userspace.

Failed targets are now added to the target list and configfs, but
remain disabled until manually enabled or reconfigured. This change does
not change the behaviour if CONFIG_NETCONSOLE_DYNAMIC is not set.

CC: Aijay Adams <aijay@meta.com>
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20240822111051.179850-3-leitao@debian.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/netconsole.c

@@ -1258,11 +1258,18 @@ static struct netconsole_target *alloc_param_target(char *target_config,
 		goto fail;
 
 	err = netpoll_setup(&nt->np);
-	if (err)
-		goto fail;
-
+	if (err) {
+		pr_err("Not enabling netconsole for %s%d. Netpoll setup failed\n",
+		       NETCONSOLE_PARAM_TARGET_PREFIX, cmdline_count);
+		if (!IS_ENABLED(CONFIG_NETCONSOLE_DYNAMIC))
+			/* only fail if dynamic reconfiguration is set,
+			 * otherwise, keep the target in the list, but disabled.
+			 */
+			goto fail;
+	} else {
+		nt->enabled = true;
+	}
 	populate_configfs_item(nt, cmdline_count);
-	nt->enabled = true;
 
 	return nt;