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![Tejun Heo](/assets/img/avatar_default.png)
printk logbuf keeps various metadata and optional key=value dictionary for structured messages, both of which are stripped when messages are handed to regular console drivers. It can be useful to have this metadata and dictionary available to netconsole consumers. This obviously makes logging via netconsole more complete and the sequence number in particular is useful in environments where messages may be lost or reordered in transit - e.g. when netconsole is used to collect messages in a large cluster where packets may have to travel congested hops to reach the aggregator. The lost and reordered messages can easily be identified and handled accordingly using the sequence numbers. printk recently added extended console support which can be selected by setting CON_EXTENDED flag. From console driver side, not much changes. The only difference is that the text passed to the write callback is formatted the same way as /dev/kmsg. This patch implements extended console support for netconsole which can be enabled by either prepending "+" to a netconsole boot param entry or echoing 1 to "extended" file in configfs. When enabled, netconsole transmits extended log messages with headers identical to /dev/kmsg output. There's one complication due to message fragments. netconsole limits the maximum message size to 1k and messages longer than that are split into multiple fragments. As all extended console messages should carry matching headers and be uniquely identifiable, each extended message fragment carries full copy of the metadata and an extra header field to identify the specific fragment. The optional header is of the form "ncfrag=OFF/LEN" where OFF is the byte offset into the message body and LEN is the total length. To avoid unnecessarily making printk format extended messages, Extended netconsole is registered with printk when the first extended netconsole is configured. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: David Miller <davem@davemloft.net> Cc: Kay Sievers <kay@vrfy.org> Cc: Petr Mladek <pmladek@suse.cz> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
210 lines
7.7 KiB
Text
210 lines
7.7 KiB
Text
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started by Ingo Molnar <mingo@redhat.com>, 2001.09.17
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2.6 port and netpoll api by Matt Mackall <mpm@selenic.com>, Sep 9 2003
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IPv6 support by Cong Wang <xiyou.wangcong@gmail.com>, Jan 1 2013
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Extended console support by Tejun Heo <tj@kernel.org>, May 1 2015
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Please send bug reports to Matt Mackall <mpm@selenic.com>
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Satyam Sharma <satyam.sharma@gmail.com>, and Cong Wang <xiyou.wangcong@gmail.com>
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Introduction:
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=============
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This module logs kernel printk messages over UDP allowing debugging of
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problem where disk logging fails and serial consoles are impractical.
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It can be used either built-in or as a module. As a built-in,
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netconsole initializes immediately after NIC cards and will bring up
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the specified interface as soon as possible. While this doesn't allow
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capture of early kernel panics, it does capture most of the boot
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process.
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Sender and receiver configuration:
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==================================
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It takes a string configuration parameter "netconsole" in the
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following format:
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netconsole=[+][src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]
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where
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+ if present, enable extended console support
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src-port source for UDP packets (defaults to 6665)
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src-ip source IP to use (interface address)
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dev network interface (eth0)
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tgt-port port for logging agent (6666)
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tgt-ip IP address for logging agent
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tgt-macaddr ethernet MAC address for logging agent (broadcast)
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Examples:
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linux netconsole=4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc
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or
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insmod netconsole netconsole=@/,@10.0.0.2/
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or using IPv6
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insmod netconsole netconsole=@/,@fd00:1:2:3::1/
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It also supports logging to multiple remote agents by specifying
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parameters for the multiple agents separated by semicolons and the
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complete string enclosed in "quotes", thusly:
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modprobe netconsole netconsole="@/,@10.0.0.2/;@/eth1,6892@10.0.0.3/"
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Built-in netconsole starts immediately after the TCP stack is
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initialized and attempts to bring up the supplied dev at the supplied
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address.
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The remote host has several options to receive the kernel messages,
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for example:
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1) syslogd
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2) netcat
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On distributions using a BSD-based netcat version (e.g. Fedora,
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openSUSE and Ubuntu) the listening port must be specified without
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the -p switch:
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'nc -u -l -p <port>' / 'nc -u -l <port>' or
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'netcat -u -l -p <port>' / 'netcat -u -l <port>'
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3) socat
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'socat udp-recv:<port> -'
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Dynamic reconfiguration:
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========================
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Dynamic reconfigurability is a useful addition to netconsole that enables
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remote logging targets to be dynamically added, removed, or have their
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parameters reconfigured at runtime from a configfs-based userspace interface.
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[ Note that the parameters of netconsole targets that were specified/created
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from the boot/module option are not exposed via this interface, and hence
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cannot be modified dynamically. ]
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To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
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netconsole module (or kernel, if netconsole is built-in).
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Some examples follow (where configfs is mounted at the /sys/kernel/config
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mountpoint).
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To add a remote logging target (target names can be arbitrary):
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cd /sys/kernel/config/netconsole/
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mkdir target1
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Note that newly created targets have default parameter values (as mentioned
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above) and are disabled by default -- they must first be enabled by writing
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"1" to the "enabled" attribute (usually after setting parameters accordingly)
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as described below.
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To remove a target:
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rmdir /sys/kernel/config/netconsole/othertarget/
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The interface exposes these parameters of a netconsole target to userspace:
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enabled Is this target currently enabled? (read-write)
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extended Extended mode enabled (read-write)
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dev_name Local network interface name (read-write)
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local_port Source UDP port to use (read-write)
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remote_port Remote agent's UDP port (read-write)
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local_ip Source IP address to use (read-write)
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remote_ip Remote agent's IP address (read-write)
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local_mac Local interface's MAC address (read-only)
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remote_mac Remote agent's MAC address (read-write)
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The "enabled" attribute is also used to control whether the parameters of
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a target can be updated or not -- you can modify the parameters of only
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disabled targets (i.e. if "enabled" is 0).
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To update a target's parameters:
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cat enabled # check if enabled is 1
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echo 0 > enabled # disable the target (if required)
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echo eth2 > dev_name # set local interface
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echo 10.0.0.4 > remote_ip # update some parameter
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echo cb:a9:87:65:43:21 > remote_mac # update more parameters
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echo 1 > enabled # enable target again
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You can also update the local interface dynamically. This is especially
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useful if you want to use interfaces that have newly come up (and may not
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have existed when netconsole was loaded / initialized).
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Extended console:
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=================
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If '+' is prefixed to the configuration line or "extended" config file
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is set to 1, extended console support is enabled. An example boot
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param follows.
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linux netconsole=+4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc
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Log messages are transmitted with extended metadata header in the
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following format which is the same as /dev/kmsg.
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<level>,<sequnum>,<timestamp>,<contflag>;<message text>
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Non printable characters in <message text> are escaped using "\xff"
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notation. If the message contains optional dictionary, verbatim
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newline is used as the delimeter.
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If a message doesn't fit in certain number of bytes (currently 1000),
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the message is split into multiple fragments by netconsole. These
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fragments are transmitted with "ncfrag" header field added.
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ncfrag=<byte-offset>/<total-bytes>
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For example, assuming a lot smaller chunk size, a message "the first
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chunk, the 2nd chunk." may be split as follows.
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6,416,1758426,-,ncfrag=0/31;the first chunk,
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6,416,1758426,-,ncfrag=16/31; the 2nd chunk.
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Miscellaneous notes:
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====================
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WARNING: the default target ethernet setting uses the broadcast
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ethernet address to send packets, which can cause increased load on
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other systems on the same ethernet segment.
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TIP: some LAN switches may be configured to suppress ethernet broadcasts
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so it is advised to explicitly specify the remote agents' MAC addresses
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from the config parameters passed to netconsole.
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TIP: to find out the MAC address of, say, 10.0.0.2, you may try using:
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ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2
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TIP: in case the remote logging agent is on a separate LAN subnet than
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the sender, it is suggested to try specifying the MAC address of the
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default gateway (you may use /sbin/route -n to find it out) as the
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remote MAC address instead.
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NOTE: the network device (eth1 in the above case) can run any kind
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of other network traffic, netconsole is not intrusive. Netconsole
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might cause slight delays in other traffic if the volume of kernel
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messages is high, but should have no other impact.
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NOTE: if you find that the remote logging agent is not receiving or
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printing all messages from the sender, it is likely that you have set
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the "console_loglevel" parameter (on the sender) to only send high
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priority messages to the console. You can change this at runtime using:
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dmesg -n 8
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or by specifying "debug" on the kernel command line at boot, to send
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all kernel messages to the console. A specific value for this parameter
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can also be set using the "loglevel" kernel boot option. See the
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dmesg(8) man page and Documentation/kernel-parameters.txt for details.
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Netconsole was designed to be as instantaneous as possible, to
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enable the logging of even the most critical kernel bugs. It works
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from IRQ contexts as well, and does not enable interrupts while
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sending packets. Due to these unique needs, configuration cannot
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be more automatic, and some fundamental limitations will remain:
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only IP networks, UDP packets and ethernet devices are supported.
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