Commit 29e36c9f authored by Jim Cromie's avatar Jim Cromie Committed by Greg Kroah-Hartman

dynamic_debug: update Documentation/*, Kconfig.debug

In dynamic-debug-howto.txt:

- add section: Debug Messages at Module Initialization Time
- update flags indicators in example outputs to include '='
- make flags descriptions tabular
- add item on '_' flag-char
- add dyndbg, boot-args examples
- rewrap some paragraphs with long lines

In Kconfig.debug, note that compiling with -DDEBUG enables all
pr_debug()s in that code.

In kernel-parameters.txt, add dyndbg and module.dyndbg items,
and deprecate ddebug_query.
Signed-off-by: default avatarJim Cromie <jim.cromie@gmail.com>
Acked-by: default avatarJason Baron <jbaron@redhat.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 8e59b5cf
......@@ -2,17 +2,17 @@
Introduction
============
This document describes how to use the dynamic debug (ddebug) feature.
This document describes how to use the dynamic debug (dyndbg) feature.
Dynamic debug is designed to allow you to dynamically enable/disable kernel
code to obtain additional kernel information. Currently, if
CONFIG_DYNAMIC_DEBUG is set, then all pr_debug()/dev_dbg() calls can be
dynamically enabled per-callsite.
Dynamic debug is designed to allow you to dynamically enable/disable
kernel code to obtain additional kernel information. Currently, if
CONFIG_DYNAMIC_DEBUG is set, then all pr_debug()/dev_dbg() calls can
be dynamically enabled per-callsite.
Dynamic debug has even more useful features:
* Simple query language allows turning on and off debugging statements by
matching any combination of 0 or 1 of:
* Simple query language allows turning on and off debugging
statements by matching any combination of 0 or 1 of:
- source filename
- function name
......@@ -20,17 +20,19 @@ Dynamic debug has even more useful features:
- module name
- format string
* Provides a debugfs control file: <debugfs>/dynamic_debug/control which can be
read to display the complete list of known debug statements, to help guide you
* Provides a debugfs control file: <debugfs>/dynamic_debug/control
which can be read to display the complete list of known debug
statements, to help guide you
Controlling dynamic debug Behaviour
===================================
The behaviour of pr_debug()/dev_dbg()s are controlled via writing to a
control file in the 'debugfs' filesystem. Thus, you must first mount the debugfs
filesystem, in order to make use of this feature. Subsequently, we refer to the
control file as: <debugfs>/dynamic_debug/control. For example, if you want to
enable printing from source file 'svcsock.c', line 1603 you simply do:
control file in the 'debugfs' filesystem. Thus, you must first mount
the debugfs filesystem, in order to make use of this feature.
Subsequently, we refer to the control file as:
<debugfs>/dynamic_debug/control. For example, if you want to enable
printing from source file 'svcsock.c', line 1603 you simply do:
nullarbor:~ # echo 'file svcsock.c line 1603 +p' >
<debugfs>/dynamic_debug/control
......@@ -44,15 +46,15 @@ nullarbor:~ # echo 'file svcsock.c wtf 1 +p' >
Viewing Dynamic Debug Behaviour
===========================
You can view the currently configured behaviour of all the debug statements
via:
You can view the currently configured behaviour of all the debug
statements via:
nullarbor:~ # cat <debugfs>/dynamic_debug/control
# filename:lineno [module]function flags format
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:323 [svcxprt_rdma]svc_rdma_cleanup - "SVCRDMA Module Removed, deregister RPC RDMA transport\012"
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init - "\011max_inline : %d\012"
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init - "\011sq_depth : %d\012"
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init - "\011max_requests : %d\012"
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:323 [svcxprt_rdma]svc_rdma_cleanup =_ "SVCRDMA Module Removed, deregister RPC RDMA transport\012"
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init =_ "\011max_inline : %d\012"
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init =_ "\011sq_depth : %d\012"
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init =_ "\011max_requests : %d\012"
...
......@@ -65,12 +67,12 @@ nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control | wc -l
nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control | wc -l
42
Note in particular that the third column shows the enabled behaviour
flags for each debug statement callsite (see below for definitions of the
flags). The default value, no extra behaviour enabled, is "-". So
you can view all the debug statement callsites with any non-default flags:
The third column shows the currently enabled flags for each debug
statement callsite (see below for definitions of the flags). The
default value, with no flags enabled, is "=_". So you can view all
the debug statement callsites with any non-default flags:
nullarbor:~ # awk '$3 != "-"' <debugfs>/dynamic_debug/control
nullarbor:~ # awk '$3 != "=_"' <debugfs>/dynamic_debug/control
# filename:lineno [module]function flags format
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c:1603 [sunrpc]svc_send p "svc_process: st_sendto returned %d\012"
......@@ -103,15 +105,14 @@ specifications, followed by a flags change specification.
command ::= match-spec* flags-spec
The match-spec's are used to choose a subset of the known dprintk()
The match-spec's are used to choose a subset of the known pr_debug()
callsites to which to apply the flags-spec. Think of them as a query
with implicit ANDs between each pair. Note that an empty list of
match-specs is possible, but is not very useful because it will not
match any debug statement callsites.
match-specs will select all debug statement callsites.
A match specification comprises a keyword, which controls the attribute
of the callsite to be compared, and a value to compare against. Possible
keywords are:
A match specification comprises a keyword, which controls the
attribute of the callsite to be compared, and a value to compare
against. Possible keywords are:
match-spec ::= 'func' string |
'file' string |
......@@ -164,15 +165,15 @@ format
characters (") or single quote characters (').
Examples:
format svcrdma: // many of the NFS/RDMA server dprintks
format readahead // some dprintks in the readahead cache
format svcrdma: // many of the NFS/RDMA server pr_debugs
format readahead // some pr_debugs in the readahead cache
format nfsd:\040SETATTR // one way to match a format with whitespace
format "nfsd: SETATTR" // a neater way to match a format with whitespace
format 'nfsd: SETATTR' // yet another way to match a format with whitespace
line
The given line number or range of line numbers is compared
against the line number of each dprintk() callsite. A single
against the line number of each pr_debug() callsite. A single
line number matches the callsite line number exactly. A
range of line numbers matches any callsite between the first
and last line number inclusive. An empty first number means
......@@ -188,51 +189,93 @@ The flags specification comprises a change operation followed
by one or more flag characters. The change operation is one
of the characters:
-
remove the given flags
+
add the given flags
=
set the flags to the given flags
- remove the given flags
+ add the given flags
= set the flags to the given flags
The flags are:
f
Include the function name in the printed message
l
Include line number in the printed message
m
Include module name in the printed message
p
Causes a printk() message to be emitted to dmesg
t
Include thread ID in messages not generated from interrupt context
p enables the pr_debug() callsite.
f Include the function name in the printed message
l Include line number in the printed message
m Include module name in the printed message
t Include thread ID in messages not generated from interrupt context
_ No flags are set. (Or'd with others on input)
For display, the flags are preceded by '='
(mnemonic: what the flags are currently equal to).
Note the regexp ^[-+=][flmpt]+$ matches a flags specification.
Note also that there is no convenient syntax to remove all
the flags at once, you need to use "-flmpt".
Note the regexp ^[-+=][flmpt_]+$ matches a flags specification.
To clear all flags at once, use "=_" or "-flmpt".
Debug messages during boot process
Debug messages during Boot Process
==================================
To be able to activate debug messages during the boot process,
even before userspace and debugfs exists, use the boot parameter:
ddebug_query="QUERY"
To activate debug messages for core code and built-in modules during
the boot process, even before userspace and debugfs exists, use
dyndbg="QUERY", module.dyndbg="QUERY", or ddebug_query="QUERY"
(ddebug_query is obsoleted by dyndbg, and deprecated). QUERY follows
the syntax described above, but must not exceed 1023 characters. Your
bootloader may impose lower limits.
These dyndbg params are processed just after the ddebug tables are
processed, as part of the arch_initcall. Thus you can enable debug
messages in all code run after this arch_initcall via this boot
parameter.
QUERY follows the syntax described above, but must not exceed 1023
characters. The enablement of debug messages is done as an arch_initcall.
Thus you can enable debug messages in all code processed after this
arch_initcall via this boot parameter.
On an x86 system for example ACPI enablement is a subsys_initcall and
ddebug_query="file ec.c +p"
dyndbg="file ec.c +p"
will show early Embedded Controller transactions during ACPI setup if
your machine (typically a laptop) has an Embedded Controller.
PCI (or other devices) initialization also is a hot candidate for using
this boot parameter for debugging purposes.
If foo module is not built-in, foo.dyndbg will still be processed at
boot time, without effect, but will be reprocessed when module is
loaded later. dyndbg_query= and bare dyndbg= are only processed at
boot.
Debug Messages at Module Initialization Time
============================================
When "modprobe foo" is called, modprobe scans /proc/cmdline for
foo.params, strips "foo.", and passes them to the kernel along with
params given in modprobe args or /etc/modprob.d/*.conf files,
in the following order:
1. # parameters given via /etc/modprobe.d/*.conf
options foo dyndbg=+pt
options foo dyndbg # defaults to +p
2. # foo.dyndbg as given in boot args, "foo." is stripped and passed
foo.dyndbg=" func bar +p; func buz +mp"
3. # args to modprobe
modprobe foo dyndbg==pmf # override previous settings
These dyndbg queries are applied in order, with last having final say.
This allows boot args to override or modify those from /etc/modprobe.d
(sensible, since 1 is system wide, 2 is kernel or boot specific), and
modprobe args to override both.
In the foo.dyndbg="QUERY" form, the query must exclude "module foo".
"foo" is extracted from the param-name, and applied to each query in
"QUERY", and only 1 match-spec of each type is allowed.
The dyndbg option is a "fake" module parameter, which means:
- modules do not need to define it explicitly
- every module gets it tacitly, whether they use pr_debug or not
- it doesnt appear in /sys/module/$module/parameters/
To see it, grep the control file, or inspect /proc/cmdline.
For CONFIG_DYNAMIC_DEBUG kernels, any settings given at boot-time (or
enabled by -DDEBUG flag during compilation) can be disabled later via
the sysfs interface if the debug messages are no longer needed:
echo "module module_name -p" > <debugfs>/dynamic_debug/control
Examples
========
......@@ -260,3 +303,18 @@ nullarbor:~ # echo -n 'func svc_process -p' >
// enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
<debugfs>/dynamic_debug/control
// enable all messages
nullarbor:~ # echo -n '+p' > <debugfs>/dynamic_debug/control
// add module, function to all enabled messages
nullarbor:~ # echo -n '+mf' > <debugfs>/dynamic_debug/control
// boot-args example, with newlines and comments for readability
Kernel command line: ...
// see whats going on in dyndbg=value processing
dynamic_debug.verbose=1
// enable pr_debugs in 2 builtins, #cmt is stripped
dyndbg="module params +p #cmt ; module sys +p"
// enable pr_debugs in 2 functions in a module loaded later
pc87360.dyndbg="func pc87360_init_device +p; func pc87360_find +p"
......@@ -610,7 +610,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
time. See Documentation/dynamic-debug-howto.txt for
details.
details. Deprecated, see dyndbg.
debug [KNL] Enable kernel debugging (events log level).
......@@ -730,6 +730,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
dscc4.setup= [NET]
dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
module.dyndbg[="val"]
Enable debug messages at boot time. See
Documentation/dynamic-debug-howto.txt for details.
earlycon= [KNL] Output early console device and options.
uart[8250],io,<addr>[,options]
uart[8250],mmio,<addr>[,options]
......
......@@ -1205,8 +1205,13 @@ config DYNAMIC_DEBUG
otherwise be available at runtime. These messages can then be
enabled/disabled based on various levels of scope - per source file,
function, module, format string, and line number. This mechanism
implicitly enables all pr_debug() and dev_dbg() calls. The impact of
this compile option is a larger kernel text size of about 2%.
implicitly compiles in all pr_debug() and dev_dbg() calls, which
enlarges the kernel text size by about 2%.
If a source file is compiled with DEBUG flag set, any
pr_debug() calls in it are enabled by default, but can be
disabled at runtime as below. Note that DEBUG flag is
turned on by many CONFIG_*DEBUG* options.
Usage:
......@@ -1223,16 +1228,16 @@ config DYNAMIC_DEBUG
lineno : line number of the debug statement
module : module that contains the debug statement
function : function that contains the debug statement
flags : 'p' means the line is turned 'on' for printing
flags : '=p' means the line is turned 'on' for printing
format : the format used for the debug statement
From a live system:
nullarbor:~ # cat <debugfs>/dynamic_debug/control
# filename:lineno [module]function flags format
fs/aio.c:222 [aio]__put_ioctx - "__put_ioctx:\040freeing\040%p\012"
fs/aio.c:248 [aio]ioctx_alloc - "ENOMEM:\040nr_events\040too\040high\012"
fs/aio.c:1770 [aio]sys_io_cancel - "calling\040cancel\012"
fs/aio.c:222 [aio]__put_ioctx =_ "__put_ioctx:\040freeing\040%p\012"
fs/aio.c:248 [aio]ioctx_alloc =_ "ENOMEM:\040nr_events\040too\040high\012"
fs/aio.c:1770 [aio]sys_io_cancel =_ "calling\040cancel\012"
Example usage:
......
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