[PATCH net-next v2 0/3] net: netconsole: configfs entries for boot target

[PATCH net-next v2 0/3] net: netconsole: configfs entries for boot target

[Breno Leitao]

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


Change Log:
===========
 * V1 -> V2:
	* Replaced the name of the NETCONSOLE_PARAM_TARGET_NAME macro
	* Improved the code documentation
	* Improved the user documentation

Breno Leitao (3):
  netconsole: Initialize configfs_item for default targets
  netconsole: Attach cmdline target to dynamic target
  Documentation: netconsole: add support for cmdline targets

 Documentation/networking/netconsole.rst | 22 ++++++++--
 drivers/net/netconsole.c                | 55 ++++++++++++++++++++++++-
 2 files changed, 72 insertions(+), 5 deletions(-)

-- 
2.34.1

[PATCH net-next v2 1/3] netconsole: Initialize configfs_item for default targets

[Breno Leitao]

For netconsole targets allocated during the boot time (passing
netconsole=... argument), netconsole_target->item is not initialized.
That is not a problem because it is not used inside configfs.

An upcoming patch will be using it, thus, initialize the targets with
the name 'cmdline' plus a counter starting from 0.  This name will match
entries in the configfs later.

Suggested-by: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/net/netconsole.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 3111e1648592..7c46cf1c923e 100644
--- a/drivers/net/netconsole.c
+++ b/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_NAME "cmdline"
+
 #ifndef	MODULE
 static int __init option_setup(char *opt)
 {
@@ -108,6 +110,8 @@ struct netconsole_target {
 	struct netpoll		np;
 };
 
+static void populate_configfs_item(struct netconsole_target *nt,
+				   int cmdline_count);
 #ifdef	CONFIG_NETCONSOLE_DYNAMIC
 
 static struct configfs_subsystem netconsole_subsys;
@@ -165,6 +169,10 @@ 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.
@@ -193,7 +201,8 @@ static struct netconsole_target *alloc_and_init(void)
 }
 
 /* Allocate new target (from boot/module param) and setup netpoll for it */
-static struct netconsole_target *alloc_param_target(char *target_config)
+static struct netconsole_target *alloc_param_target(char *target_config,
+						    int cmdline_count)
 {
 	struct netconsole_target *nt;
 	int err;
@@ -228,6 +237,7 @@ static struct netconsole_target *alloc_param_target(char *target_config)
 	if (err)
 		goto fail;
 
+	populate_configfs_item(nt, cmdline_count);
 	nt->enabled = true;
 
 	return nt;
@@ -740,6 +750,17 @@ 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_NAME, cmdline_count);
+	config_item_init_type_name(&nt->item, target_name,
+				   &netconsole_target_type);
+}
+
 #endif	/* CONFIG_NETCONSOLE_DYNAMIC */
 
 /* Handle network interface device notifications */
@@ -954,6 +975,7 @@ 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 +983,7 @@ 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 +999,7 @@ 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++;
 		}
 	}
 
-- 
2.34.1

[PATCH net-next v2 2/3] netconsole: Attach cmdline target to dynamic target

[Breno Leitao]

Enable the attachment of a dynamic target to the target created during
boot time. The boot-time targets are named as "cmdline\d", where "\d" is
a number starting at 0.

If the user creates a dynamic target named "cmdline0", it will attach to
the first target created at boot time (as defined in the
`netconsole=...` command line argument). `cmdline1` will attach to the
second target and so forth.

If there is no netconsole target created at boot time, then, the target
name could be reused.

Relevant design discussion:
https://lore.kernel.org/all/ZRWRal5bW93px4km@gmail.com/

Suggested-by: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/net/netconsole.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 7c46cf1c923e..4aa40e2e4c86 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -685,6 +685,23 @@ 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.
  */
@@ -695,6 +712,17 @@ 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_NAME,
+		     strlen(NETCONSOLE_PARAM_TARGET_NAME))) {
+		nt = find_cmdline_target(name);
+		if (nt)
+			return &nt->item;
+	}
+
 	nt = alloc_and_init();
 	if (!nt)
 		return ERR_PTR(-ENOMEM);
-- 
2.34.1

[PATCH net-next v2 3/3] Documentation: netconsole: add support for cmdline targets

[Breno Leitao]

With the previous patches, there is no more limitation at modifying the
targets created at boot time (or module load time).

Document the way on how to create the configfs directories to be able to
modify these netconsole targets.

The design discussion about this topic could be found at:
https://lore.kernel.org/all/ZRWRal5bW93px4km@gmail.com/

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 Documentation/networking/netconsole.rst | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/Documentation/networking/netconsole.rst b/Documentation/networking/netconsole.rst
index 7a9de0568e84..390730a74332 100644
--- a/Documentation/networking/netconsole.rst
+++ b/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:
 =================
 
-- 
2.34.1

Re: [PATCH net-next v2 1/3] netconsole: Initialize configfs_item for default targets

[Jakub Kicinski]

On Thu,  5 Oct 2023 05:36:34 -0700 Breno Leitao wrote:
> +static void populate_configfs_item(struct netconsole_target *nt,
> +				   int cmdline_count);

Could you move alloc / free_param_target() to avoid the forward
declaration? (separate patch)

Re: [PATCH net-next v2 1/3] netconsole: Initialize configfs_item for default targets

[Breno Leitao]

On Mon, Oct 09, 2023 at 07:31:58PM -0700, Jakub Kicinski wrote:
> On Thu,  5 Oct 2023 05:36:34 -0700 Breno Leitao wrote:
> > +static void populate_configfs_item(struct netconsole_target *nt,
> > +				   int cmdline_count);
> 
> Could you move alloc / free_param_target() to avoid the forward
> declaration? (separate patch)

Yes, this is a good idea. I tried to avoid the forward declaration, but
I didn't find this solution. Sending a v3 with this change.

Thanks for the review!