dynamic debug: update docs
updates the documentation for 'dynamic debug' feature. Signed-off-by: Greg Banks <gnb@sgi.com> Signed-off-by: Jason Baron <jbaron@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Jason Baron
Greg Kroah-Hartman
parent
e9d376f0fa
commit
86151fdf38
2 changed files with 273 additions and 31 deletions
232
Documentation/dynamic-debug-howto.txt
Normal file
232
Documentation/dynamic-debug-howto.txt
Normal file
|
|
@ -0,0 +1,232 @@
|
|||
|
||||
Introduction
|
||||
============
|
||||
|
||||
This document describes how to use the dynamic debug (ddebug) 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_debug() 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:
|
||||
|
||||
- source filename
|
||||
- function name
|
||||
- line number (including ranges of line numbers)
|
||||
- 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
|
||||
|
||||
Controlling dynamic debug Behaviour
|
||||
===============================
|
||||
|
||||
The behaviour of pr_debug()/dev_debug()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:
|
||||
|
||||
nullarbor:~ # echo 'file svcsock.c line 1603 +p' >
|
||||
<debugfs>/dynamic_debug/control
|
||||
|
||||
If you make a mistake with the syntax, the write will fail thus:
|
||||
|
||||
nullarbor:~ # echo 'file svcsock.c wtf 1 +p' >
|
||||
<debugfs>/dynamic_debug/control
|
||||
-bash: echo: write error: Invalid argument
|
||||
|
||||
Viewing Dynamic Debug Behaviour
|
||||
===========================
|
||||
|
||||
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\040Module\040Removed,\040deregister\040RPC\040RDMA\040transport\012"
|
||||
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init - "\011max_inline\040\040\040\040\040\040\040:\040%d\012"
|
||||
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init - "\011sq_depth\040\040\040\040\040\040\040\040\040:\040%d\012"
|
||||
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init - "\011max_requests\040\040\040\040\040:\040%d\012"
|
||||
...
|
||||
|
||||
|
||||
You can also apply standard Unix text manipulation filters to this
|
||||
data, e.g.
|
||||
|
||||
nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control | wc -l
|
||||
62
|
||||
|
||||
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:
|
||||
|
||||
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:\040st_sendto\040returned\040%d\012"
|
||||
|
||||
|
||||
Command Language Reference
|
||||
==========================
|
||||
|
||||
At the lexical level, a command comprises a sequence of words separated
|
||||
by whitespace characters. Note that newlines are treated as word
|
||||
separators and do *not* end a command or allow multiple commands to
|
||||
be done together. So these are all equivalent:
|
||||
|
||||
nullarbor:~ # echo -c 'file svcsock.c line 1603 +p' >
|
||||
<debugfs>/dynamic_debug/control
|
||||
nullarbor:~ # echo -c ' file svcsock.c line 1603 +p ' >
|
||||
<debugfs>/dynamic_debug/control
|
||||
nullarbor:~ # echo -c 'file svcsock.c\nline 1603 +p' >
|
||||
<debugfs>/dynamic_debug/control
|
||||
nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
|
||||
<debugfs>/dynamic_debug/control
|
||||
|
||||
Commands are bounded by a write() system call. If you want to do
|
||||
multiple commands you need to do a separate "echo" for each, like:
|
||||
|
||||
nullarbor:~ # echo 'file svcsock.c line 1603 +p' > /proc/dprintk ;\
|
||||
> echo 'file svcsock.c line 1563 +p' > /proc/dprintk
|
||||
|
||||
or even like:
|
||||
|
||||
nullarbor:~ # (
|
||||
> echo 'file svcsock.c line 1603 +p' ;\
|
||||
> echo 'file svcsock.c line 1563 +p' ;\
|
||||
> ) > /proc/dprintk
|
||||
|
||||
At the syntactical level, a command comprises a sequence of match
|
||||
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()
|
||||
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.
|
||||
|
||||
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 |
|
||||
'module' string |
|
||||
'format' string |
|
||||
'line' line-range
|
||||
|
||||
line-range ::= lineno |
|
||||
'-'lineno |
|
||||
lineno'-' |
|
||||
lineno'-'lineno
|
||||
// Note: line-range cannot contain space, e.g.
|
||||
// "1-30" is valid range but "1 - 30" is not.
|
||||
|
||||
lineno ::= unsigned-int
|
||||
|
||||
The meanings of each keyword are:
|
||||
|
||||
func
|
||||
The given string is compared against the function name
|
||||
of each callsite. Example:
|
||||
|
||||
func svc_tcp_accept
|
||||
|
||||
file
|
||||
The given string is compared against either the full
|
||||
pathname or the basename of the source file of each
|
||||
callsite. Examples:
|
||||
|
||||
file svcsock.c
|
||||
file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c
|
||||
|
||||
module
|
||||
The given string is compared against the module name
|
||||
of each callsite. The module name is the string as
|
||||
seen in "lsmod", i.e. without the directory or the .ko
|
||||
suffix and with '-' changed to '_'. Examples:
|
||||
|
||||
module sunrpc
|
||||
module nfsd
|
||||
|
||||
format
|
||||
The given string is searched for in the dynamic debug format
|
||||
string. Note that the string does not need to match the
|
||||
entire format, only some part. Whitespace and other
|
||||
special characters can be escaped using C octal character
|
||||
escape \ooo notation, e.g. the space character is \040.
|
||||
Examples:
|
||||
|
||||
format svcrdma: // many of the NFS/RDMA server dprintks
|
||||
format readahead // some dprintks in the readahead cache
|
||||
format nfsd:\040SETATTR // how 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
|
||||
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
|
||||
the first line in the file, an empty line number means the
|
||||
last number in the file. Examples:
|
||||
|
||||
line 1603 // exactly line 1603
|
||||
line 1600-1605 // the six lines from line 1600 to line 1605
|
||||
line -1605 // the 1605 lines from line 1 to line 1605
|
||||
line 1600- // all lines from line 1600 to the end of the file
|
||||
|
||||
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
|
||||
|
||||
The flags are:
|
||||
|
||||
p
|
||||
Causes a printk() message to be emitted to dmesg
|
||||
|
||||
Note the regexp ^[-+=][scp]+$ matches a flags specification.
|
||||
Note also that there is no convenient syntax to remove all
|
||||
the flags at once, you need to use "-psc".
|
||||
|
||||
Examples
|
||||
========
|
||||
|
||||
// enable the message at line 1603 of file svcsock.c
|
||||
nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
|
||||
<debugfs>/dynamic_debug/control
|
||||
|
||||
// enable all the messages in file svcsock.c
|
||||
nullarbor:~ # echo -n 'file svcsock.c +p' >
|
||||
<debugfs>/dynamic_debug/control
|
||||
|
||||
// enable all the messages in the NFS server module
|
||||
nullarbor:~ # echo -n 'module nfsd +p' >
|
||||
<debugfs>/dynamic_debug/control
|
||||
|
||||
// enable all 12 messages in the function svc_process()
|
||||
nullarbor:~ # echo -n 'func svc_process +p' >
|
||||
<debugfs>/dynamic_debug/control
|
||||
|
||||
// disable all 12 messages in the function svc_process()
|
||||
nullarbor:~ # echo -n 'func svc_process -p' >
|
||||
<debugfs>/dynamic_debug/control
|
||||
|
|
@ -848,59 +848,69 @@ config BUILD_DOCSRC
|
|||
Say N if you are unsure.
|
||||
|
||||
config DYNAMIC_DEBUG
|
||||
bool "Enable dynamic printk() call support"
|
||||
bool "Enable dynamic printk() support"
|
||||
default n
|
||||
depends on PRINTK
|
||||
depends on DEBUG_FS
|
||||
select PRINTK_DEBUG
|
||||
help
|
||||
|
||||
Compiles debug level messages into the kernel, which would not
|
||||
otherwise be available at runtime. These messages can then be
|
||||
enabled/disabled on a per module basis. 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%.
|
||||
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%.
|
||||
|
||||
Usage:
|
||||
|
||||
Dynamic debugging is controlled by the debugfs file,
|
||||
dynamic_printk/modules. This file contains a list of the modules that
|
||||
can be enabled. The format of the file is the module name, followed
|
||||
by a set of flags that can be enabled. The first flag is always the
|
||||
'enabled' flag. For example:
|
||||
Dynamic debugging is controlled via the 'dynamic_debug/ddebug' file,
|
||||
which is contained in the 'debugfs' filesystem. Thus, the debugfs
|
||||
filesystem must first be mounted before making use of this feature.
|
||||
We refer the control file as: <debugfs>/dynamic_debug/ddebug. This
|
||||
file contains a list of the debug statements that can be enabled. The
|
||||
format for each line of the file is:
|
||||
|
||||
<module_name> <enabled=0/1>
|
||||
.
|
||||
.
|
||||
.
|
||||
filename:lineno [module]function flags format
|
||||
|
||||
<module_name> : Name of the module in which the debug call resides
|
||||
<enabled=0/1> : whether the messages are enabled or not
|
||||
filename : source file of the debug statement
|
||||
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
|
||||
format : the format used for the debug statement
|
||||
|
||||
From a live system:
|
||||
|
||||
snd_hda_intel enabled=0
|
||||
fixup enabled=0
|
||||
driver enabled=0
|
||||
nullarbor:~ # cat <debugfs>/dynamic_debug/ddebug
|
||||
# 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"
|
||||
|
||||
Enable a module:
|
||||
Example usage:
|
||||
|
||||
$echo "set enabled=1 <module_name>" > dynamic_printk/modules
|
||||
// enable the message at line 1603 of file svcsock.c
|
||||
nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
|
||||
<debugfs>/dynamic_debug/ddebug
|
||||
|
||||
Disable a module:
|
||||
// enable all the messages in file svcsock.c
|
||||
nullarbor:~ # echo -n 'file svcsock.c +p' >
|
||||
<debugfs>/dynamic_debug/ddebug
|
||||
|
||||
$echo "set enabled=0 <module_name>" > dynamic_printk/modules
|
||||
// enable all the messages in the NFS server module
|
||||
nullarbor:~ # echo -n 'module nfsd +p' >
|
||||
<debugfs>/dynamic_debug/ddebug
|
||||
|
||||
Enable all modules:
|
||||
// enable all 12 messages in the function svc_process()
|
||||
nullarbor:~ # echo -n 'func svc_process +p' >
|
||||
<debugfs>/dynamic_debug/ddebug
|
||||
|
||||
$echo "set enabled=1 all" > dynamic_printk/modules
|
||||
// disable all 12 messages in the function svc_process()
|
||||
nullarbor:~ # echo -n 'func svc_process -p' >
|
||||
<debugfs>/dynamic_debug/ddebug
|
||||
|
||||
Disable all modules:
|
||||
|
||||
$echo "set enabled=0 all" > dynamic_printk/modules
|
||||
|
||||
Finally, passing "dynamic_printk" at the command line enables
|
||||
debugging for all modules. This mode can be turned off via the above
|
||||
disable command.
|
||||
See Documentation/dynamic-debug-howto.txt for additional information.
|
||||
|
||||
source "samples/Kconfig"
|
||||
|
||||
|
|
|
|||
Loading…
Reference in a new issue