path: root/Documentation
diff options
authorSatyam Sharma <satyam@infradead.org>2007-08-10 15:35:05 -0700
committerDavid S. Miller <davem@sunset.davemloft.net>2007-10-10 16:48:06 -0700
commit0bcc1816188e570bde1d56a208996660f2633ae0 (patch)
tree8104c0b0c54a93a510b4b9b50a45cbaabad245f4 /Documentation
parent[NET] netconsole: Support multiple logging targets (diff)
[NET] netconsole: Support dynamic reconfiguration using configfs
Based upon initial work by Keiichi Kii <k-keiichi@bx.jp.nec.com>. 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. (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 the "enabled" attribute. Thus, netpoll_setup() is then called on the set parameters in the context of _this_ write(2) on the "enabled" attribute itself. This design enables the user to reconfigure existing netconsole targets at runtime to be attached to newly-come-up interfaces that may not have existed when netconsole was loaded or when the targets were actually created. All this effectively enables us to get rid of custom ioctls. (3) Ultra-paranoid configfs attribute show() and store() operations, with sanity and input range checking, using only safe string primitives, and compliant with the recommendations in Documentation/filesystems/sysfs.txt. (4) A new function netpoll_print_options() is created in the netpoll API, that just prints out the configured parameters for a netpoll structure. netpoll_parse_options() is modified to use that and it is also exported to be used from netconsole. Signed-off-by: Satyam Sharma <satyam@infradead.org> Acked-by: Keiichi Kii <k-keiichi@bx.jp.nec.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'Documentation')
1 files changed, 68 insertions, 0 deletions
diff --git a/Documentation/networking/netconsole.txt b/Documentation/networking/netconsole.txt
index 1aaa7383e41d..3c2f2b328638 100644
--- a/Documentation/networking/netconsole.txt
+++ b/Documentation/networking/netconsole.txt
@@ -3,6 +3,10 @@ started by Ingo Molnar <mingo@redhat.com>, 2001.09.17
2.6 port and netpoll api by Matt Mackall <mpm@selenic.com>, Sep 9 2003
Please send bug reports to Matt Mackall <mpm@selenic.com>
+and Satyam Sharma <satyam.sharma@gmail.com>
This module logs kernel printk messages over UDP allowing debugging of
problem where disk logging fails and serial consoles are impractical.
@@ -13,6 +17,9 @@ the specified interface as soon as possible. While this doesn't allow
capture of early kernel panics, it does capture most of the boot
+Sender and receiver configuration:
It takes a string configuration parameter "netconsole" in the
following format:
@@ -46,6 +53,67 @@ address.
The remote host can run either 'netcat -u -l -p <port>' or syslogd.
+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).
+Some examples follow (where configfs is mounted at the /sys/kernel/config
+To add a remote logging target (target names can be arbitrary):
+ cd /sys/kernel/config/netconsole/
+ mkdir target1
+Note that newly created targets have default parameter values (as mentioned
+above) and are disabled by default -- they must first be enabled by writing
+"1" to the "enabled" attribute (usually after setting parameters accordingly)
+as described below.
+To remove a target:
+ rmdir /sys/kernel/config/netconsole/othertarget/
+The interface exposes these parameters of a netconsole target to userspace:
+ enabled Is this target currently enabled? (read-write)
+ dev_name Local network interface name (read-write)
+ local_port Source UDP port to use (read-write)
+ remote_port Remote agent's UDP port (read-write)
+ local_ip Source IP address to use (read-write)
+ remote_ip Remote agent's IP address (read-write)
+ local_mac Local interface's MAC address (read-only)
+ remote_mac Remote agent's MAC address (read-write)
+The "enabled" attribute is also used to control whether the parameters of
+a target can be updated or not -- you can modify the parameters of only
+disabled targets (i.e. if "enabled" is 0).
+To update a target's parameters:
+ cat enabled # check if enabled is 1
+ echo 0 > enabled # disable the target (if required)
+ echo eth2 > dev_name # set local interface
+ echo > remote_ip # update some parameter
+ echo cb:a9:87:65:43:21 > remote_mac # update more parameters
+ echo 1 > enabled # enable target again
+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).
+Miscellaneous notes:
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.