Merge branch 'net-netconsole-configfs-entries-for-boot-target'

Breno Leitao says:

====================
net: netconsole: configfs entries for boot target

There is a limitation in netconsole, where it is impossible to
disable or modify the target created from the command line parameter.
(netconsole=...).

"netconsole" cmdline parameter sets the remote IP, and if the remote IP
changes, the machine needs to be rebooted (with the new remote IP set in
the command line parameter).

This allows the user to modify a target without the need to restart the
machine.

This functionality sits on top of the dynamic target reconfiguration that is
already implemented in netconsole.

The way to modify a boot time target is creating special named configfs
directories, that will be associated with the targets coming from
`netconsole=...`.

Example:

Let's suppose you have two netconsole targets defined at boot time::

 netconsole=4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc;4444@10.0.0.1/eth1,9353@10.0.0.3/12:34:56:78:9a:bc

You can modify these targets in runtime by creating the following targets::

 $ mkdir cmdline1
 $ cat cmdline1/remote_ip
 10.0.0.3
 $ echo 0 > cmdline1/enabled
 $ echo 10.0.0.4 > cmdline1/remote_ip
 $ echo 1 > cmdline1/enabled
====================

Link: https://lore.kernel.org/r/20231012111401.333798-1-leitao@debian.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/networking/netconsole.rst

@@ -99,9 +99,6 @@ Dynamic reconfiguration:
 Dynamic reconfigurability is a useful addition to netconsole that enables
 remote logging targets to be dynamically added, removed, or have their
 parameters reconfigured at runtime from a configfs-based userspace interface.
-[ Note that the parameters of netconsole targets that were specified/created
-from the boot/module option are not exposed via this interface, and hence
-cannot be modified dynamically. ]
 
 To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
 netconsole module (or kernel, if netconsole is built-in).
@@ -155,6 +152,25 @@ You can also update the local interface dynamically. This is especially
 useful if you want to use interfaces that have newly come up (and may not
 have existed when netconsole was loaded / initialized).
 
+Netconsole targets defined at boot time (or module load time) with the
+`netconsole=` param are assigned the name `cmdline<index>`.  For example, the
+first target in the parameter is named `cmdline0`.  You can control and modify
+these targets by creating configfs directories with the matching name.
+
+Let's suppose you have two netconsole targets defined at boot time::
+
+ netconsole=4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc;4444@10.0.0.1/eth1,9353@10.0.0.3/12:34:56:78:9a:bc
+
+You can modify these targets in runtime by creating the following targets::
+
+ mkdir cmdline0
+ cat cmdline0/remote_ip
+ 10.0.0.2
+
+ mkdir cmdline1
+ cat cmdline1/remote_ip
+ 10.0.0.3
+
 Extended console:
 =================
 

drivers/net/netconsole.c

@@ -53,6 +53,8 @@ static bool oops_only = false;
 module_param(oops_only, bool, 0600);
 MODULE_PARM_DESC(oops_only, "Only log oops messages");
 
+#define NETCONSOLE_PARAM_TARGET_PREFIX "cmdline"
+
 #ifndef	MODULE
 static int __init option_setup(char *opt)
 {
@@ -165,6 +167,10 @@ static void netconsole_target_put(struct netconsole_target *nt)
 {
 }
 
+static void populate_configfs_item(struct netconsole_target *nt,
+				   int cmdline_count)
+{
+}
 #endif	/* CONFIG_NETCONSOLE_DYNAMIC */
 
 /* Allocate and initialize with defaults.
@@ -192,58 +198,6 @@ static struct netconsole_target *alloc_and_init(void)
 	return nt;
 }
 
-/* Allocate new target (from boot/module param) and setup netpoll for it */
-static struct netconsole_target *alloc_param_target(char *target_config)
-{
-	struct netconsole_target *nt;
-	int err;
-
-	nt = alloc_and_init();
-	if (!nt) {
-		err = -ENOMEM;
-		goto fail;
-	}
-
-	if (*target_config == '+') {
-		nt->extended = true;
-		target_config++;
-	}
-
-	if (*target_config == 'r') {
-		if (!nt->extended) {
-			pr_err("Netconsole configuration error. Release feature requires extended log message");
-			err = -EINVAL;
-			goto fail;
-		}
-		nt->release = true;
-		target_config++;
-	}
-
-	/* Parse parameters and setup netpoll */
-	err = netpoll_parse_options(&nt->np, target_config);
-	if (err)
-		goto fail;
-
-	err = netpoll_setup(&nt->np);
-	if (err)
-		goto fail;
-
-	nt->enabled = true;
-
-	return nt;
-
-fail:
-	kfree(nt);
-	return ERR_PTR(err);
-}
-
-/* Cleanup netpoll for given target (from boot/module param) and free it */
-static void free_param_target(struct netconsole_target *nt)
-{
-	netpoll_cleanup(&nt->np);
-	kfree(nt);
-}
-
 #ifdef	CONFIG_NETCONSOLE_DYNAMIC
 
 /*
@@ -675,6 +629,23 @@ static const struct config_item_type netconsole_target_type = {
 	.ct_owner		= THIS_MODULE,
 };
 
+static struct netconsole_target *find_cmdline_target(const char *name)
+{
+	struct netconsole_target *nt, *ret = NULL;
+	unsigned long flags;
+
+	spin_lock_irqsave(&target_list_lock, flags);
+	list_for_each_entry(nt, &target_list, list) {
+		if (!strcmp(nt->item.ci_name, name)) {
+			ret = nt;
+			break;
+		}
+	}
+	spin_unlock_irqrestore(&target_list_lock, flags);
+
+	return ret;
+}
+
 /*
  * Group operations and type for netconsole_subsys.
  */
@@ -685,6 +656,17 @@ static struct config_item *make_netconsole_target(struct config_group *group,
 	struct netconsole_target *nt;
 	unsigned long flags;
 
+	/* Checking if a target by this name was created at boot time.  If so,
+	 * attach a configfs entry to that target.  This enables dynamic
+	 * control.
+	 */
+	if (!strncmp(name, NETCONSOLE_PARAM_TARGET_PREFIX,
+		     strlen(NETCONSOLE_PARAM_TARGET_PREFIX))) {
+		nt = find_cmdline_target(name);
+		if (nt)
+			return &nt->item;
+	}
+
 	nt = alloc_and_init();
 	if (!nt)
 		return ERR_PTR(-ENOMEM);
@@ -740,6 +722,17 @@ static struct configfs_subsystem netconsole_subsys = {
 	},
 };
 
+static void populate_configfs_item(struct netconsole_target *nt,
+				   int cmdline_count)
+{
+	char target_name[16];
+
+	snprintf(target_name, sizeof(target_name), "%s%d",
+		 NETCONSOLE_PARAM_TARGET_PREFIX, cmdline_count);
+	config_item_init_type_name(&nt->item, target_name,
+				   &netconsole_target_type);
+}
+
 #endif	/* CONFIG_NETCONSOLE_DYNAMIC */
 
 /* Handle network interface device notifications */
@@ -938,6 +931,60 @@ static void write_msg(struct console *con, const char *msg, unsigned int len)
 	spin_unlock_irqrestore(&target_list_lock, flags);
 }
 
+/* Allocate new target (from boot/module param) and setup netpoll for it */
+static struct netconsole_target *alloc_param_target(char *target_config,
+						    int cmdline_count)
+{
+	struct netconsole_target *nt;
+	int err;
+
+	nt = alloc_and_init();
+	if (!nt) {
+		err = -ENOMEM;
+		goto fail;
+	}
+
+	if (*target_config == '+') {
+		nt->extended = true;
+		target_config++;
+	}
+
+	if (*target_config == 'r') {
+		if (!nt->extended) {
+			pr_err("Netconsole configuration error. Release feature requires extended log message");
+			err = -EINVAL;
+			goto fail;
+		}
+		nt->release = true;
+		target_config++;
+	}
+
+	/* Parse parameters and setup netpoll */
+	err = netpoll_parse_options(&nt->np, target_config);
+	if (err)
+		goto fail;
+
+	err = netpoll_setup(&nt->np);
+	if (err)
+		goto fail;
+
+	populate_configfs_item(nt, cmdline_count);
+	nt->enabled = true;
+
+	return nt;
+
+fail:
+	kfree(nt);
+	return ERR_PTR(err);
+}
+
+/* Cleanup netpoll for given target (from boot/module param) and free it */
+static void free_param_target(struct netconsole_target *nt)
+{
+	netpoll_cleanup(&nt->np);
+	kfree(nt);
+}
+
 static struct console netconsole_ext = {
 	.name	= "netcon_ext",
 	.flags	= CON_ENABLED | CON_EXTENDED,
@@ -954,6 +1001,7 @@ static int __init init_netconsole(void)
 {
 	int err;
 	struct netconsole_target *nt, *tmp;
+	unsigned int count = 0;
 	bool extended = false;
 	unsigned long flags;
 	char *target_config;
@@ -961,7 +1009,7 @@ static int __init init_netconsole(void)
 
 	if (strnlen(input, MAX_PARAM_LENGTH)) {
 		while ((target_config = strsep(&input, ";"))) {
-			nt = alloc_param_target(target_config);
+			nt = alloc_param_target(target_config, count);
 			if (IS_ERR(nt)) {
 				err = PTR_ERR(nt);
 				goto fail;
@@ -977,6 +1025,7 @@ static int __init init_netconsole(void)
 			spin_lock_irqsave(&target_list_lock, flags);
 			list_add(&nt->list, &target_list);
 			spin_unlock_irqrestore(&target_list_lock, flags);
+			count++;
 		}
 	}