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

[PATCH 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

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 | 21 ++++++++--
 drivers/net/netconsole.c                | 51 ++++++++++++++++++++++++-
 2 files changed, 67 insertions(+), 5 deletions(-)

-- 
2.34.1

[PATCH 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..b68456054a0c 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 DEFAULT_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",
+		 DEFAULT_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 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 | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index b68456054a0c..6235f56dc652 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 +712,13 @@ static struct config_item *make_netconsole_target(struct config_group *group,
 	struct netconsole_target *nt;
 	unsigned long flags;
 
+	/* Checking if there is a target created populated at boot time */
+	if (!strncmp(name, DEFAULT_TARGET_NAME, strlen(DEFAULT_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 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 | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/Documentation/networking/netconsole.rst b/Documentation/networking/netconsole.rst
index 7a9de0568e84..b25c89608e50 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 +152,24 @@ 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).
 
+You can control and modify the targets defined at boot time (or module load
+time) by creating special targets names. These special targets are named
+`cmdline` concatenated to an integer, example: `cmdline0`.
+
+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 1/3] netconsole: Initialize configfs_item for default targets

[Joel Becker]

On Mon, Oct 02, 2023 at 08:53:47AM -0700, Breno Leitao wrote:
> diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
> index 3111e1648592..b68456054a0c 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 DEFAULT_TARGET_NAME "cmdline"
> +

I'm not sure `DEFAULT` is the right terminology here.  e.g. it's not a
default for dynamic targets, etc.  Perhaps `BOOT_TARGET_NAME` or
`NETCONSOLE_PARAM_TARGET_NAME`?

Joel

-- 

"Friends may come and go, but enemies accumulate." 
        - Thomas Jones

			http://www.jlbec.org/
			jlbec@evilplan.org

Re: [PATCH 2/3] netconsole: Attach cmdline target to dynamic target

[Joel Becker]

On Mon, Oct 02, 2023 at 08:53:48AM -0700, Breno Leitao wrote:
> 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 | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
> index b68456054a0c..6235f56dc652 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 +712,13 @@ static struct config_item *make_netconsole_target(struct config_group *group,
>  	struct netconsole_target *nt;
>  	unsigned long flags;
>  
> +	/* Checking if there is a target created populated at boot time */

Perhaps a little clearer:

```
       /* 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, DEFAULT_TARGET_NAME, strlen(DEFAULT_TARGET_NAME))) {
> +		nt = find_cmdline_target(name);
> +		if (nt)
> +			return &nt->item;
> +	}
> +

Thanks,
Joel

-- 

Life's Little Instruction Book #356

	"Be there when people need you."

			http://www.jlbec.org/
			jlbec@evilplan.org

Re: [PATCH 3/3] Documentation: netconsole: add support for cmdline targets

[Joel Becker]

On Mon, Oct 02, 2023 at 08:53:49AM -0700, Breno Leitao wrote:
> @@ -155,6 +152,24 @@ 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).
>  
> +You can control and modify the targets defined at boot time (or module load
> +time) by creating special targets names. These special targets are named
> +`cmdline` concatenated to an integer, example: `cmdline0`.

The special names are already "created", so perhaps it's a little
clearer to say something like:

```
+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
> +

And of course keep the examples as you've described them.

Thanks,
Joel

-- 

Life's Little Instruction Book #337

	"Reread your favorite book."

			http://www.jlbec.org/
			jlbec@evilplan.org

Re: [PATCH 3/3] Documentation: netconsole: add support for cmdline targets

[Breno Leitao]

On Wed, Oct 04, 2023 at 01:09:16PM -0700, Joel Becker wrote:
> On Mon, Oct 02, 2023 at 08:53:49AM -0700, Breno Leitao wrote:
> > @@ -155,6 +152,24 @@ 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).
> >  
> > +You can control and modify the targets defined at boot time (or module load
> > +time) by creating special targets names. These special targets are named
> > +`cmdline` concatenated to an integer, example: `cmdline0`.
> 
> The special names are already "created", so perhaps it's a little
> clearer to say something like:
> 
> ```
> +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.
> ```

That is way better. Thanks for the review.
I will send an updated version soon.