[0/9] netconsole: Multiple targets and dynamic reconfigurability
This patchset is a rework of the original idea and patches posted by

Keiichi Kii and Takayoshi Kochi at: http://lkml.org/lkml/2007/6/13/72
This is v2 of the patchset, the previous version is available at:

http://lkml.org/lkml/2007/7/4/107
This is diffed against 2.6.22-rc6-mm1 + the earlier netpoll fixlet and the

configfs cleanup patches (those are already merged in -mm AFAIK, and hence

not reproduced here).
[1/9] netconsole: Cleanups, codingstyle, prettyfication

[2/9] netconsole: Remove bogus check

[3/9] netconsole: Simplify boot/module option setup logic

[4/9] netconsole: Add some useful tips to documentation

[5/9] netconsole: Introduce netconsole_target

[6/9] netconsole: Introduce netconsole_netdev_notifier

[7/9] netconsole: Use netif_running() in write_msg()

[8/9] netconsole: Support multiple logging targets

[9/9] netconsole: Support dynamic reconfiguration using configfs
Changes since v1:

=================
* Split / merge various patches in the patchset as suggested in reviews.
* Get rid of redundant "id" and "dev_status" fields.
* Use netif_running() instead of IFF_UP.
* Explain the boot/module option setup simplification and the netdev

  notifier patches in more detail (justify why they're good / required).
* Get rid of possible trailing newline from echo(1) in store_dev_name().
* Fix a panic bug -- now, when no boot/module option is specified, we

  skip only the part that creates and inserts param string-created

  targets. Rest of the initialization (notifier, configfs subsystem)

  is done as usual.
* Get rid of lock-skipping special-casing where possible.
* Use config_item_name() instead of "empty_item".
* Introduce netpoll_print_options() in netpoll and use it.
* Style cleanups (reduce #ifdefs, indentation, whitespace fixes, etc).
* Miscellaneous fixes in documentation (as suggested in reviews).
About this patchset:

====================
What?
Support multiple remote ...
[ message continues ]

I tested your v2 patches on the x86/IA64 architecture.

There was no problem on my tests.
Signed-off-by: Keiichi Kii <k-keiichi@bx.jp.nec.com>
Thanks

--

Keiichi KII

NEC Corporation OSS Platform Development Division

E-mail: k-keiichi@bx.jp.nec.com

-

Hi Keiichi,
Ok, thanks! I'll send out the next series (with the various few

fixes and cleanups suggested this time) with your Sign-offs/Acks.
Satyam

-

Hi Satyam,
I'm going to test/review these patches and report the result of tests 
Thanks

--

Keiichi KII

NEC Corporation OSS Platform Development Division

E-mail: k-keiichi@bx.jp.nec.com

-

From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
[6/9] netconsole: Introduce netconsole_netdev_notifier
To update fields of underlying netpoll structure at runtime on

corresponding NETDEV_CHANGEADDR or NETDEV_CHANGENAME notifications.
ioctl(SIOCSIFHWADDR) {or ioctl(SIOCSIFNAME)} could be used to change the

hardware/MAC address {or name} of the local interface that our netpoll is

attached to. Whenever this happens, netdev notifier chain is called out

with the NETDEV_CHANGEADDR {or NETDEV_CHANGENAME} event message. We respond

to that and update the local_mac {or dev_name} field of the struct netpoll.

This makes sense anyway, but is especially required for dynamic netconsole

because the netpoll structure's internal members become user visible files

when either sysfs or configfs are used. So this helps us to keep up with the

MAC address / name changes and keep the values in struct netpoll uptodate.
Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>

Cc: Keiichi Kii <k-keiichi@bx.jp.nec.com>
---
 drivers/net/netconsole.c |   32 ++++++++++++++++++++++++++++++++

 1 file changed, 32 insertions(+)
---
diff -ruNp a/drivers/net/netconsole.c b/drivers/net/netconsole.c

--- a/drivers/net/netconsole.c	2007-07-10 06:57:44.000000000 +0530

+++ b/drivers/net/netconsole.c	2007-07-10 07:24:27.000000000 +0530

@@ -80,6 +80,33 @@ static struct netconsole_target default_

 	},

 };
+/* Handle network interface device notifications */

+static int netconsole_netdev_event(struct notifier_block *this,

+				   unsigned long event,

+				   void *ptr)

+{

+	struct net_device *dev = ptr;

+	struct netconsole_target *nt = &default_target;

+

+	if (nt->np.dev == dev) {

+		switch (event) {

+		case NETDEV_CHANGEADDR:

+			memcpy(nt->np.local_mac, dev->dev_addr, ETH_ALEN);

+			break;

+

+		case NETDEV_CHANGENAME:

+			strlcpy(nt->np.dev_name, dev->name, IFNAMSIZ);

+			break;

+		}

+	}

+

+	return NOTIFY_DONE;

+}

+

+static struct notifier_block netconsole_netde...
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Thanks

--

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NEC Corporation OSS Platform Development Division

E-mail: k-keiichi@bx.jp.nec.com
-

From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
[8/9] netconsole: Support multiple logging targets
This patch introduces support for multiple targets:
Let's keep this out of CONFIG_NETCONSOLE_DYNAMIC as well -- this is useful

even in the default case and (including the infrastructure introduced in

previous patches) doesn't really add too many bytes to module text. All the

complexity (and size) comes with the dynamic reconfigurability / userspace

interface patch, and so it's plausible users may want to keep this enabled

but that disabled (say to avoid a dep on CONFIG_CONFIGFS_FS too).
Also update documentation to mention the use of ";" separator to specify

multiple logging targets in the boot/module option string.
Brief overview:
We maintain a target_list (and corresponding lock). Get rid of the static

"default_target" and introduce allocation and release functions for our

netconsole_target objects (but keeping sure to preserve previous behaviour

such as default values). During init_netconsole(), ";" is used as the

separator to identify multiple target specifications in the boot/module

option string. The target specifications are parsed and netpolls setup.

During exit, the target_list is torn down and all items released.
Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>

Cc: Keiichi Kii <k-keiichi@bx.jp.nec.com>
---
 Documentation/networking/netconsole.txt |    6 +

 drivers/net/netconsole.c                |  173 ++++++++++++++++++++++++--------

 2 files changed, 139 insertions(+), 40 deletions(-)
---
diff -ruNp a/Documentation/networking/netconsole.txt b/Documentation/networking/netconsole.txt

--- a/Documentation/networking/netconsole.txt	2007-07-10 07:35:17.000000000 +0530

+++ b/Documentation/networking/netconsole.txt	2007-07-10 08:25:17.000000000 +0530

@@ -34,6 +34,12 @@ Examples:
  insmod netconsole netconsole=@/,@10.0.0.2/
+It also supports logging to multiple remote agents by specifying

+parameters for the multiple agents separated ...
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Thanks

--

Keiichi KII

NEC Corporation OSS Platform Development Division

E-mail: k-keiichi@bx.jp.nec.com
-

Is the unlikely a good idea here? Not having any targets may be

unusual but it isn't ridiculous. It might even be a sensible default

for distros. My (very limited) understanding of unlikely is that it

could impose a very large penalty in that case and would make a very

marginal difference at best in the common case.
Cheers,

Duane.
--

"I never could learn to drink that blood and call it wine" - Bob Dylan

-

Hi,
Hmm, I put it in there because I expected that the user must have had

at least one target configured (added to target_list) if he's got the

module loaded/built-in (and netconsole registered), which is when this
I wouldn't call it a large penalty, but yeah, probably the unlikely()

there isn't all that important either.
Satyam

-

Loading the module won't happen without a config, but there's no

requirement that a built-in netconsole has a kernel command-line

argument.  I always build netconsole for my kernels.  Sure, I usually do

it as a module, but if I build a monolithic kernel I compile it in.
Joel
-- 
"When choosing between two evils, I always like to try the one

 I've never tried before."

        - Mae West
Joel Becker

Principal Software Developer

Oracle

E-mail: joel.becker@oracle.com

Phone: (650) 506-8127

-

Hi Joel,
That's no longer the case (doesn't need to be enforced actually) now

with being able to add logging targets _after_ the module has loaded

and initialized / registered itself. It's plausible a user may simply

want to load netconsole without any "netconsole=" option, and then
The above is applicable for the built-in case too, with

CONFIG_NETCONSOLE_DYNAMIC. So now built-in netconsole will initialize

(configfs subsystem, etc) and register itself (register_console) even

if no "netconsole=" was provided, again for the same reason.
And I now notice that CONFIG_NETCONSOLE=y in the defconfig's of

most arch's. So I think I did get the common case wrong there ...

ok, I'll get rid of the unlikely() in that case.
Satyam

-

From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
[5/9] netconsole: Introduce netconsole_target
Introduce a wrapper structure over netpoll to represent logging targets

configured in netconsole. This will get extended with other members in

further patches.
The original patchset did this along with (and inside the #ifdef) of

CONFIG_NETCONSOLE_DYNAMIC itself. I decided otherwise, and was able to

drastically cut down on the #ifdef-complexity of final netconsole.c.

Also, struct netconsole_target would be required for multiple targets

support also, and not just dynamic reconfigurability. Previously these

two things were coupled, but I want to de-link that (more on this later).
Note that this patch in itself looks quite redundant / stupid, but it is

purposefully made this way, so further patches are more readable.
Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>

Cc: Keiichi Kii <k-keiichi@bx.jp.nec.com>
---
 drivers/net/netconsole.c |   34 ++++++++++++++++++++++++----------

 1 file changed, 24 insertions(+), 10 deletions(-)
---
diff -ruNp a/drivers/net/netconsole.c b/drivers/net/netconsole.c

--- a/drivers/net/netconsole.c	2007-07-10 06:42:11.000000000 +0530

+++ b/drivers/net/netconsole.c	2007-07-10 06:50:46.000000000 +0530

@@ -62,24 +62,35 @@ static int __init option_setup(char *opt

 __setup("netconsole=", option_setup);

 #endif	/* MODULE */
-static struct netpoll np = {

-	.name		= "netconsole",

-	.dev_name	= "eth0",

-	.local_port	= 6665,

-	.remote_port	= 6666,

-	.remote_mac	= {0xff, 0xff, 0xff, 0xff, 0xff, 0xff},

+/**

+ * struct netconsole_target - Represents a configured netconsole target.

+ * @np:		The netpoll structure for this target.

+ */

+struct netconsole_target {

+	struct netpoll		np;

+};

+

+static struct netconsole_target default_target = {

+	.np		= {

+		.name		= "netconsole",

+		.dev_name	= "eth0",

+		.local_port	= 6665,

+		.remote_port	= 6666,

+		.remote_mac	= {0xff, 0xff, 0xff, 0xff, 0xff, 0xff},

+	},

 };
 static void ...
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Thanks

--

Keiichi KII

NEC Corporation OSS Platform Development Division

E-mail: k-keiichi@bx.jp.nec.com

-

From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
[7/9] netconsole: Use netif_running() in write_msg()
Avoid unnecessarily disabling interrupts and calling netpoll_send_udp()

if the corresponding local interface is not up.
Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>

Cc: Keiichi Kii <k-keiichi@bx.jp.nec.com>
---
 drivers/net/netconsole.c |   18 +++++++++---------

 1 file changed, 9 insertions(+), 9 deletions(-)
---
diff -ruNp a/drivers/net/netconsole.c b/drivers/net/netconsole.c

--- a/drivers/net/netconsole.c	2007-07-10 07:26:47.000000000 +0530

+++ b/drivers/net/netconsole.c	2007-07-10 07:45:51.000000000 +0530

@@ -113,16 +113,16 @@ static void write_msg(struct console *co

 	unsigned long flags;

 	struct netconsole_target *nt = &default_target;
-	local_irq_save(flags);

-

-	for (left = len; left;) {

-		frag = min(left, MAX_PRINT_CHUNK);

-		netpoll_send_udp(&nt->np, msg, frag);

-		msg += frag;

-		left -= frag;

+	if (netif_running(nt->np.dev)) {

+		local_irq_save(flags);

+		for (left = len; left;) {

+			frag = min(left, MAX_PRINT_CHUNK);

+			netpoll_send_udp(&nt->np, msg, frag);

+			msg += frag;

+			left -= frag;

+		}

+		local_irq_restore(flags);

 	}

-

-	local_irq_restore(flags);

 }
 static struct console netconsole = {

-

Acked-by: Keiichi Kii <k-keiichi@bx.jp.nec.com>
Thanks

--

Keiichi KII

NEC Corporation OSS Platform Development Division

E-mail: k-keiichi@bx.jp.nec.com
-

From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
[2/9] netconsole: Remove bogus check
The (!np.dev) check in write_msg() is bogus (always false), because:

np.dev is set by netpoll_setup(), which is called by the target init

code in init_netconsole() _before_ register_console() => write_msg() cannot

be triggered unless netpoll_setup() returns with success. And that will not

happen if netpoll_setup() failed to set np.dev. Also np.dev cannot go from

under us while netconsole is loaded. This is because netpoll_setup() grabs

a reference for us on that dev. So let's remove the pointless check.
Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>

Cc: Keiichi Kii <k-keiichi@bx.jp.nec.com>
---
 drivers/net/netconsole.c |    3 ---

 1 file changed, 3 deletions(-)
---
diff -ruNp a/drivers/net/netconsole.c b/drivers/net/netconsole.c

--- a/drivers/net/netconsole.c	2007-07-10 05:53:42.000000000 +0530

+++ b/drivers/net/netconsole.c	2007-07-10 05:55:00.000000000 +0530

@@ -67,9 +67,6 @@ static void write_msg(struct console *co

 	int frag, left;

 	unsigned long flags;
-	if (!np.dev)

-		return;

-

 	local_irq_save(flags);
 	for (left = len; left;) {

-

Acked-by: Keiichi Kii <k-keiichi@bx.jp.nec.com>
Thanks

--

Keiichi KII

NEC Corporation OSS Platform Development Division

E-mail: k-keiichi@bx.jp.nec.com

-

Acked-by: Matt Mackall <mpm@selenic.com>
--

Mathematics is the supreme nostalgia of our time.

-

From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
[3/9] netconsole: Simplify boot/module option setup logic
Presently, for built-in netconsole:
__setup(..., option_setup) ensures that the option_setup() function is

called at boot-time from obsolete_checksetup() with the string matching

"netconsole=" passed to it from the kernel's command line. We call the

netpoll_parse_options() from in there, and populate the netpoll struct

with the passed values. Then, when init_netconsole() is called during the

initcall phase, strlen(config) fails, thus skipping option_setup().
For modular netconsole:
module_param_string() ensures that the string corresponding to the

"netconsole" module parameter passed from the modprobe command line is

copied into the "config" static variable. This time, when the module is

being initialized, strlen(config) is true and so option_setup() is called

on "config" from init_netconsole() and the input string is parsed and the

netpoll struct populated.
Hence, quite different things happen in the copying and parsing of the

passed netpoll parameters for the modular / built-in cases. This patch

makes both of them similar by doing exactly the equivalent of a

module_param_string() in option_setup() also -- just copying the param

string passed from the kernel command line into the "config" static

variable. So, init_netconsole() parses (using netpoll_parse_options())

it in both the cases, and makes the logic somewhat simpler.
Now, option_setup() is only ever called / used for the built-in case,

so we put it inside a #ifndef MODULE, otherwise gcc will complain about

option_setup() being "defined but not used".
Also, the "configured" variable is redundant with this patch and so removed.
Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>

Cc: Keiichi Kii <k-keiichi@bx.jp.nec.com>
---
 drivers/net/netconsole.c |   27 ++++++++++++++-------------

 1 file changed, 14 insertions(+), 13 deletions(-)
---
diff -ruNp a/drivers/net/netconsole.c b/d...
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Thanks

--

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NEC Corporation OSS Platform Development Division

E-mail: k-keiichi@bx.jp.nec.com

-

Acked-by: Matt Mackall <mpm@selenic.com>
--

Mathematics is the supreme nostalgia of our time.

-

From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
[9/9] netconsole: Support dynamic reconfiguration using configfs
This patch introduces support for dynamic reconfiguration (adding, removing

and/or modifying parameters of netconsole targets at runtime) using a

userspace interface exported via configfs. Documentation is also updated

accordingly.
Issues and brief design overview:
(1) Kernel-initiated creation / destruction of kernel objects is not

possible with configfs -- the lifetimes of the "config items" is managed

exclusively from userspace. But netconsole must support boot/module params

too, and these are parsed in kernel and hence netpolls must be setup from

the kernel. Joel Becker suggested to separately manage the lifetimes of

the two kinds of netconsole_target objects -- those created via configfs

mkdir(2) from userspace and those specified from the boot/module option

string. This adds complexity and some redundancy here and also means that

boot/module param-created targets are not exposed through the configfs

namespace (and hence cannot be updated / destroyed dynamically). However,

this saves us from locking / refcounting complexities that would need to

be introduced in configfs to support kernel-initiated item creation /

destroy there. Also, this is similar to present behaviour in any case so

not really a problem.
(2) In configfs, item creation takes place in the call chain of the mkdir(2)

syscall in the driver subsystem. If we used an ioctl(2) to create / destroy

objects from userspace, the special userspace program is able to fill out

the structure to be passed into the ioctl and hence specify attributes such

as local interface that are required at the time we set up the netpoll.

For configfs, this information is not available at the time of mkdir(2).

So, we keep all newly-created targets (via configfs) disabled by default.

The user is expected to set various attributes appropriately (including the

local network interface if required) and then write(2) "1" to th...
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--

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NEC Corporation OSS Platform Development Division

E-mail: k-keiichi@bx.jp.nec.com
-

If CONFIG_NETCONSOLE_DYNAMIC is unset, we can't access to the "enabled" member.

So, the compile errors occur because the following functions make use of 
I created the following patch for performing some tests.

If there is nothing wrong with the patch, I'm going to continue to test.
Signed-off-by: Keiichi Kii <k-keiichi@bx.jp.nec.com>
Index: mm/drivers/net/netconsole.c

===================================================================

--- mm.orig/drivers/net/netconsole.c

+++ mm/drivers/net/netconsole.c

@@ -94,8 +94,8 @@ struct netconsole_target {

        struct list_head        list;

 #ifdef CONFIG_NETCONSOLE_DYNAMIC

        struct config_item      item;

-       int                     enabled;

 #endif

+       int                     enabled;

        struct netpoll          np;

 };
Thanks

--

Keiichi KII

NEC Corporation OSS Platform Development Division

E-mail: k-keiichi@bx.jp.nec.com

-

Hi,
Yup, enabled should be out of CONFIG_NETCONSOLE_DYNAMIC. I'll include this

change in the next version as well.
Thanks,

Satyam

-

From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
[1/9] netconsole: Cleanups, codingstyle, prettyfication
(1) Remove unwanted headers.

(2) Mark __init and __exit as appropriate.

(3) Various trivial codingstyle and prettification stuff.
Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>

Cc: Keiichi Kii <k-keiichi@bx.jp.nec.com>
---
 drivers/net/netconsole.c |   55 +++++++++++++++++++++++------------------------

 1 file changed, 27 insertions(+), 28 deletions(-)
---
diff -ruNp a/drivers/net/netconsole.c b/drivers/net/netconsole.c

--- a/drivers/net/netconsole.c	2007-04-26 08:38:32.000000000 +0530

+++ b/drivers/net/netconsole.c	2007-07-03 20:27:17.000000000 +0530

@@ -35,35 +35,32 @@

  ****************************************************************/
 #include <linux/mm.h>

-#include <linux/tty.h>

 #include <linux/init.h>

 #include <linux/module.h>

 #include <linux/console.h>

-#include <linux/tty_driver.h>

 #include <linux/moduleparam.h>

 #include <linux/string.h>

-#include <linux/sysrq.h>

-#include <linux/smp.h>

 #include <linux/netpoll.h>
 MODULE_AUTHOR("Maintainer: Matt Mackall <mpm@selenic.com>");

 MODULE_DESCRIPTION("Console driver for network interfaces");

 MODULE_LICENSE("GPL");
-static char config[256];

-module_param_string(netconsole, config, 256, 0);

+#define MAX_PARAM_LENGTH	256

+#define MAX_PRINT_CHUNK		1000

+

+static char config[MAX_PARAM_LENGTH];

+module_param_string(netconsole, config, MAX_PARAM_LENGTH, 0);

 MODULE_PARM_DESC(netconsole, " netconsole=[src-port]@[src-ip]/[dev],[tgt-port]@<tgt-ip>/[tgt-macaddr]\n");
 static struct netpoll np = {

-	.name = "netconsole",

-	.dev_name = "eth0",

-	.local_port = 6665,

-	.remote_port = 6666,

-	.remote_mac = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff},

+	.name		= "netconsole",

+	.dev_name	= "eth0",

+	.local_port	= 6665,

+	.remote_port	= 6666,

+	.remote_mac	= {0xff, 0xff, 0xff, 0xff, 0xff, 0xff},

 };

-stat...
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Thanks

--

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NEC Corporation OSS Platform Development Division

E-mail: k-keiichi@bx.jp.nec.com

-

I don't much like what you've done in (3) because I personally think

tabs should never appear anywhere but at the beginning of a line.

Which is why we consistently ask for people not to mix codingstyle

bits with substantive changes.
But what the hell..
Acked-by: Matt Mackall <mpm@selenic.com>
--

Mathematics is the supreme nostalgia of our time.

-

From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
[4/9] netconsole: Add some useful tips to documentation
Add some useful general-purpose tips.
Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>

Cc: Keiichi Kii <k-keiichi@bx.jp.nec.com>
---
 Documentation/networking/netconsole.txt |   13 +++++++++++++

 1 file changed, 13 insertions(+)
---
diff -ruNp a/Documentation/networking/netconsole.txt b/Documentation/networking/netconsole.txt

--- a/Documentation/networking/netconsole.txt	2007-04-26 08:38:32.000000000 +0530

+++ b/Documentation/networking/netconsole.txt	2007-07-10 07:31:12.000000000 +0530

@@ -44,6 +44,19 @@ WARNING: the default target ethernet set

 ethernet address to send packets, which can cause increased load on

 other systems on the same ethernet segment.
+TIP: some LAN switches may be configured to suppress ethernet broadcasts

+so it is advised to explicitly specify the remote agents' MAC addresses

+from the config parameters passed to netconsole.

+

+TIP: to find out the MAC address of, say, 10.0.0.2, you may try using:

+

+ ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2

+

+TIP: in case the remote logging agent is on a separate LAN subnet than

+the sender, it is suggested to try specifying the MAC address of the

+default gateway (you may use /sbin/route -n to find it out) as the

+remote MAC address instead.

+

 NOTE: the network device (eth1 in the above case) can run any kind

 of other network traffic, netconsole is not intrusive. Netconsole

 might cause slight delays in other traffic if the volume of kernel

-

Acked-by: Matt Mackall <mpm@selenic.com>
As long as we're on the subject, I've been meaning to add a note

telling people to set their console log level to something useful, as

having that set too low is the most common problem people encounter.
--

Mathematics is the supreme nostalgia of our time.

-

How about this?
From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
Add some useful general-purpose tips.
Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>

Cc: Keiichi Kii <k-keiichi@bx.jp.nec.com>

Acked-by: Matt Mackall <mpm@selenic.com>

Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
---
 Documentation/networking/netconsole.txt |   18 ++++++++++++++++++

 1 files changed, 18 insertions(+), 0 deletions(-)
diff --git a/Documentation/networking/netconsole.txt b/Documentation/networking/netconsole.txt

index 1caa6c7..ffd5058 100644

--- a/Documentation/networking/netconsole.txt

+++ b/Documentation/networking/netconsole.txt

@@ -44,11 +44,29 @@ WARNING: the default target ethernet setting uses the broadcast

 ethernet address to send packets, which can cause increased load on

 other systems on the same ethernet segment.
+TIP: some LAN switches may be configured to suppress ethernet broadcasts

+so it is advised to explicitly specify the remote agents' MAC addresses

+from the config parameters passed to netconsole.

+

+TIP: to find out the MAC address of, say, 10.0.0.2, you may try using:

+

+ ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2

+

+TIP: in case the remote logging agent is on a separate LAN subnet than

+the sender, it is suggested to try specifying the MAC address of the

+default gateway (you may use /sbin/route -n to find it out) as the

+remote MAC address instead.

+

 NOTE: the network device (eth1 in the above case) can run any kind

 of other network traffic, netconsole is not intrusive. Netconsole

 might cause slight delays in other traffic if the volume of kernel

 messages is high, but should have no other impact.
+Some people forget to raise the kernels log_level to an

+appropriate level and thus don't see all the kernel log messages they

+expect. You can add the kernel boot option "ignore_loglevel" to see all

+messages or you can use SysRq to set the log level to a specific value.

+

 Netconsole was designed to be as ...
[ message continues ]

Hi Jesper,
IMHO something that mentions /proc/sys/kernel/printk would be better.
You don't need to have built with SysRq support for that, it's clearly

more flexible than the ignore_loglevel option and wouldn't require a

reboot either. I'll send out an updated patch shortly.
Satyam

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Why not dmesg -n?  We've been using that for years.  Or is there

some extra change in /proc/sys/kernel/printk?
Joel
-- 
"Against stupidity the Gods themselves contend in vain."

	- Friedrich von Schiller
Joel Becker

Principal Software Developer

Oracle

E-mail: joel.becker@oracle.com

Phone: (650) 506-8127

-

Yes, "dmesg -n" sounds the most straightforward. There are multiple ways

of course, for some reason I've always used /proc/sys/kernel/printk for

this (which has the extra "feature" that it accepts values greater than

8 too :-)
Satyam

-

Why not mention all the various methods, dmesg -n,

/proc/sys/kernel/printk, SysRq, ignore_loglevel  ??
--

Jesper Juhl <jesper.juhl@gmail.com>

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