241 lines
8.4 KiB
Plaintext
241 lines
8.4 KiB
Plaintext
|
|
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 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"
|
|
...
|
|
|
|
|
|
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: st_sendto returned %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.
|
|
Alternatively, the string can be enclosed in double quote
|
|
characters (") or single quote characters (').
|
|
Examples:
|
|
|
|
format svcrdma: // many of the NFS/RDMA server dprintks
|
|
format readahead // some dprintks 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
|
|
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
|
|
|
|
// enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
|
|
nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
|
|
<debugfs>/dynamic_debug/control
|