2009-02-05 23:53:15 +07:00
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Introduction
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============
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This document describes how to use the dynamic debug (ddebug) feature.
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Dynamic debug is designed to allow you to dynamically enable/disable kernel
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code to obtain additional kernel information. Currently, if
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2011-03-25 23:42:17 +07:00
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CONFIG_DYNAMIC_DEBUG is set, then all pr_debug()/dev_dbg() calls can be
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2009-02-05 23:53:15 +07:00
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dynamically enabled per-callsite.
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Dynamic debug has even more useful features:
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* Simple query language allows turning on and off debugging statements by
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dynamic_debug: process multiple debug-queries on a line
Insert ddebug_exec_queries() in place of ddebug_exec_query(). It
splits the query string on [;\n], and calls ddebug_exec_query() on
each. All queries are processed independent of errors, allowing a
query to fail, for example when a module is not installed. Empty
lines and comments are skipped. Errors are counted, and the last
error seen (negative) or the number of callsites found (0 or positive)
is returned. Return code checks are altered accordingly.
With this, multiple queries can be given in ddebug_query, allowing
more selective enabling of callsites. As a side effect, a set of
commands can be batched in:
cat cmd-file > $DBGMT/dynamic_debug/control
We dont want a ddebug_query syntax error to kill the dynamic debug
facility, so dynamic_debug_init() zeros ddebug_exec_queries()'s return
code after logging the appropriate message, so that ddebug tables are
preserved and $DBGMT/dynamic_debug/control file is created. This
would be appropriate even without accepting multiple queries.
This patch also alters ddebug_change() to return number of callsites
matched (which typically is the same as number of callsites changed).
ddebug_exec_query() also returns the number found, or a negative value
if theres a parse error on the query.
Splitting on [;\n] prevents their use in format-specs, but selecting
callsites on punctuation is brittle anyway, meaningful and selective
substrings are more typical.
Note: splitting queries on ';' before handling trailing #comments
means that a ';' also terminates a comment, and text after the ';' is
treated as another query. This trailing query will almost certainly
result in a parse error and thus have no effect other than the error
message. The double corner case with unexpected results is:
ddebug_query="func foo +p # enable foo ; +p"
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2011-12-20 05:13:21 +07:00
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matching any combination of 0 or 1 of:
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2009-02-05 23:53:15 +07:00
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- source filename
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- function name
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- line number (including ranges of line numbers)
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- module name
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- format string
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* Provides a debugfs control file: <debugfs>/dynamic_debug/control which can be
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read to display the complete list of known debug statements, to help guide you
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Controlling dynamic debug Behaviour
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2010-08-06 21:11:02 +07:00
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===================================
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2009-02-05 23:53:15 +07:00
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2011-03-25 23:42:17 +07:00
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The behaviour of pr_debug()/dev_dbg()s are controlled via writing to a
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2009-02-05 23:53:15 +07:00
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control file in the 'debugfs' filesystem. Thus, you must first mount the debugfs
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filesystem, in order to make use of this feature. Subsequently, we refer to the
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control file as: <debugfs>/dynamic_debug/control. For example, if you want to
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enable printing from source file 'svcsock.c', line 1603 you simply do:
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nullarbor:~ # echo 'file svcsock.c line 1603 +p' >
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<debugfs>/dynamic_debug/control
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If you make a mistake with the syntax, the write will fail thus:
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nullarbor:~ # echo 'file svcsock.c wtf 1 +p' >
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<debugfs>/dynamic_debug/control
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-bash: echo: write error: Invalid argument
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Viewing Dynamic Debug Behaviour
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===========================
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You can view the currently configured behaviour of all the debug statements
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via:
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nullarbor:~ # cat <debugfs>/dynamic_debug/control
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# filename:lineno [module]function flags format
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/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"
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/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init - "\011max_inline : %d\012"
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/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init - "\011sq_depth : %d\012"
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/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init - "\011max_requests : %d\012"
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2009-02-05 23:53:15 +07:00
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...
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You can also apply standard Unix text manipulation filters to this
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data, e.g.
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nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control | wc -l
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62
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nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control | wc -l
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42
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Note in particular that the third column shows the enabled behaviour
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flags for each debug statement callsite (see below for definitions of the
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flags). The default value, no extra behaviour enabled, is "-". So
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you can view all the debug statement callsites with any non-default flags:
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nullarbor:~ # awk '$3 != "-"' <debugfs>/dynamic_debug/control
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# filename:lineno [module]function flags format
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/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"
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2009-02-05 23:53:15 +07:00
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Command Language Reference
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==========================
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At the lexical level, a command comprises a sequence of words separated
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dynamic_debug: process multiple debug-queries on a line
Insert ddebug_exec_queries() in place of ddebug_exec_query(). It
splits the query string on [;\n], and calls ddebug_exec_query() on
each. All queries are processed independent of errors, allowing a
query to fail, for example when a module is not installed. Empty
lines and comments are skipped. Errors are counted, and the last
error seen (negative) or the number of callsites found (0 or positive)
is returned. Return code checks are altered accordingly.
With this, multiple queries can be given in ddebug_query, allowing
more selective enabling of callsites. As a side effect, a set of
commands can be batched in:
cat cmd-file > $DBGMT/dynamic_debug/control
We dont want a ddebug_query syntax error to kill the dynamic debug
facility, so dynamic_debug_init() zeros ddebug_exec_queries()'s return
code after logging the appropriate message, so that ddebug tables are
preserved and $DBGMT/dynamic_debug/control file is created. This
would be appropriate even without accepting multiple queries.
This patch also alters ddebug_change() to return number of callsites
matched (which typically is the same as number of callsites changed).
ddebug_exec_query() also returns the number found, or a negative value
if theres a parse error on the query.
Splitting on [;\n] prevents their use in format-specs, but selecting
callsites on punctuation is brittle anyway, meaningful and selective
substrings are more typical.
Note: splitting queries on ';' before handling trailing #comments
means that a ';' also terminates a comment, and text after the ';' is
treated as another query. This trailing query will almost certainly
result in a parse error and thus have no effect other than the error
message. The double corner case with unexpected results is:
ddebug_query="func foo +p # enable foo ; +p"
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2011-12-20 05:13:21 +07:00
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by spaces or tabs. So these are all equivalent:
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2009-02-05 23:53:15 +07:00
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nullarbor:~ # echo -c 'file svcsock.c line 1603 +p' >
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<debugfs>/dynamic_debug/control
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nullarbor:~ # echo -c ' file svcsock.c line 1603 +p ' >
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<debugfs>/dynamic_debug/control
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nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
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<debugfs>/dynamic_debug/control
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dynamic_debug: process multiple debug-queries on a line
Insert ddebug_exec_queries() in place of ddebug_exec_query(). It
splits the query string on [;\n], and calls ddebug_exec_query() on
each. All queries are processed independent of errors, allowing a
query to fail, for example when a module is not installed. Empty
lines and comments are skipped. Errors are counted, and the last
error seen (negative) or the number of callsites found (0 or positive)
is returned. Return code checks are altered accordingly.
With this, multiple queries can be given in ddebug_query, allowing
more selective enabling of callsites. As a side effect, a set of
commands can be batched in:
cat cmd-file > $DBGMT/dynamic_debug/control
We dont want a ddebug_query syntax error to kill the dynamic debug
facility, so dynamic_debug_init() zeros ddebug_exec_queries()'s return
code after logging the appropriate message, so that ddebug tables are
preserved and $DBGMT/dynamic_debug/control file is created. This
would be appropriate even without accepting multiple queries.
This patch also alters ddebug_change() to return number of callsites
matched (which typically is the same as number of callsites changed).
ddebug_exec_query() also returns the number found, or a negative value
if theres a parse error on the query.
Splitting on [;\n] prevents their use in format-specs, but selecting
callsites on punctuation is brittle anyway, meaningful and selective
substrings are more typical.
Note: splitting queries on ';' before handling trailing #comments
means that a ';' also terminates a comment, and text after the ';' is
treated as another query. This trailing query will almost certainly
result in a parse error and thus have no effect other than the error
message. The double corner case with unexpected results is:
ddebug_query="func foo +p # enable foo ; +p"
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2011-12-20 05:13:21 +07:00
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Command submissions are bounded by a write() system call.
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Multiple commands can be written together, separated by ';' or '\n'.
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2009-02-05 23:53:15 +07:00
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dynamic_debug: process multiple debug-queries on a line
Insert ddebug_exec_queries() in place of ddebug_exec_query(). It
splits the query string on [;\n], and calls ddebug_exec_query() on
each. All queries are processed independent of errors, allowing a
query to fail, for example when a module is not installed. Empty
lines and comments are skipped. Errors are counted, and the last
error seen (negative) or the number of callsites found (0 or positive)
is returned. Return code checks are altered accordingly.
With this, multiple queries can be given in ddebug_query, allowing
more selective enabling of callsites. As a side effect, a set of
commands can be batched in:
cat cmd-file > $DBGMT/dynamic_debug/control
We dont want a ddebug_query syntax error to kill the dynamic debug
facility, so dynamic_debug_init() zeros ddebug_exec_queries()'s return
code after logging the appropriate message, so that ddebug tables are
preserved and $DBGMT/dynamic_debug/control file is created. This
would be appropriate even without accepting multiple queries.
This patch also alters ddebug_change() to return number of callsites
matched (which typically is the same as number of callsites changed).
ddebug_exec_query() also returns the number found, or a negative value
if theres a parse error on the query.
Splitting on [;\n] prevents their use in format-specs, but selecting
callsites on punctuation is brittle anyway, meaningful and selective
substrings are more typical.
Note: splitting queries on ';' before handling trailing #comments
means that a ';' also terminates a comment, and text after the ';' is
treated as another query. This trailing query will almost certainly
result in a parse error and thus have no effect other than the error
message. The double corner case with unexpected results is:
ddebug_query="func foo +p # enable foo ; +p"
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2011-12-20 05:13:21 +07:00
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~# echo "func pnpacpi_get_resources +p; func pnp_assign_mem +p" \
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> <debugfs>/dynamic_debug/control
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2009-02-05 23:53:15 +07:00
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dynamic_debug: process multiple debug-queries on a line
Insert ddebug_exec_queries() in place of ddebug_exec_query(). It
splits the query string on [;\n], and calls ddebug_exec_query() on
each. All queries are processed independent of errors, allowing a
query to fail, for example when a module is not installed. Empty
lines and comments are skipped. Errors are counted, and the last
error seen (negative) or the number of callsites found (0 or positive)
is returned. Return code checks are altered accordingly.
With this, multiple queries can be given in ddebug_query, allowing
more selective enabling of callsites. As a side effect, a set of
commands can be batched in:
cat cmd-file > $DBGMT/dynamic_debug/control
We dont want a ddebug_query syntax error to kill the dynamic debug
facility, so dynamic_debug_init() zeros ddebug_exec_queries()'s return
code after logging the appropriate message, so that ddebug tables are
preserved and $DBGMT/dynamic_debug/control file is created. This
would be appropriate even without accepting multiple queries.
This patch also alters ddebug_change() to return number of callsites
matched (which typically is the same as number of callsites changed).
ddebug_exec_query() also returns the number found, or a negative value
if theres a parse error on the query.
Splitting on [;\n] prevents their use in format-specs, but selecting
callsites on punctuation is brittle anyway, meaningful and selective
substrings are more typical.
Note: splitting queries on ';' before handling trailing #comments
means that a ';' also terminates a comment, and text after the ';' is
treated as another query. This trailing query will almost certainly
result in a parse error and thus have no effect other than the error
message. The double corner case with unexpected results is:
ddebug_query="func foo +p # enable foo ; +p"
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2011-12-20 05:13:21 +07:00
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If your query set is big, you can batch them too:
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2009-02-05 23:53:15 +07:00
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dynamic_debug: process multiple debug-queries on a line
Insert ddebug_exec_queries() in place of ddebug_exec_query(). It
splits the query string on [;\n], and calls ddebug_exec_query() on
each. All queries are processed independent of errors, allowing a
query to fail, for example when a module is not installed. Empty
lines and comments are skipped. Errors are counted, and the last
error seen (negative) or the number of callsites found (0 or positive)
is returned. Return code checks are altered accordingly.
With this, multiple queries can be given in ddebug_query, allowing
more selective enabling of callsites. As a side effect, a set of
commands can be batched in:
cat cmd-file > $DBGMT/dynamic_debug/control
We dont want a ddebug_query syntax error to kill the dynamic debug
facility, so dynamic_debug_init() zeros ddebug_exec_queries()'s return
code after logging the appropriate message, so that ddebug tables are
preserved and $DBGMT/dynamic_debug/control file is created. This
would be appropriate even without accepting multiple queries.
This patch also alters ddebug_change() to return number of callsites
matched (which typically is the same as number of callsites changed).
ddebug_exec_query() also returns the number found, or a negative value
if theres a parse error on the query.
Splitting on [;\n] prevents their use in format-specs, but selecting
callsites on punctuation is brittle anyway, meaningful and selective
substrings are more typical.
Note: splitting queries on ';' before handling trailing #comments
means that a ';' also terminates a comment, and text after the ';' is
treated as another query. This trailing query will almost certainly
result in a parse error and thus have no effect other than the error
message. The double corner case with unexpected results is:
ddebug_query="func foo +p # enable foo ; +p"
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2011-12-20 05:13:21 +07:00
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~# cat query-batch-file > <debugfs>/dynamic_debug/control
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2009-02-05 23:53:15 +07:00
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At the syntactical level, a command comprises a sequence of match
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specifications, followed by a flags change specification.
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command ::= match-spec* flags-spec
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The match-spec's are used to choose a subset of the known dprintk()
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callsites to which to apply the flags-spec. Think of them as a query
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with implicit ANDs between each pair. Note that an empty list of
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match-specs is possible, but is not very useful because it will not
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match any debug statement callsites.
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A match specification comprises a keyword, which controls the attribute
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of the callsite to be compared, and a value to compare against. Possible
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keywords are:
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match-spec ::= 'func' string |
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'file' string |
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'module' string |
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'format' string |
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'line' line-range
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line-range ::= lineno |
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'-'lineno |
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lineno'-' |
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lineno'-'lineno
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// Note: line-range cannot contain space, e.g.
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// "1-30" is valid range but "1 - 30" is not.
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lineno ::= unsigned-int
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The meanings of each keyword are:
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func
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The given string is compared against the function name
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of each callsite. Example:
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func svc_tcp_accept
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file
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The given string is compared against either the full pathname, the
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src-root relative pathname, or the basename of the source file of
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each callsite. Examples:
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file svcsock.c
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file kernel/freezer.c
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file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c
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module
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The given string is compared against the module name
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of each callsite. The module name is the string as
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seen in "lsmod", i.e. without the directory or the .ko
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suffix and with '-' changed to '_'. Examples:
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module sunrpc
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module nfsd
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format
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The given string is searched for in the dynamic debug format
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string. Note that the string does not need to match the
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entire format, only some part. Whitespace and other
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special characters can be escaped using C octal character
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escape \ooo notation, e.g. the space character is \040.
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Alternatively, the string can be enclosed in double quote
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characters (") or single quote characters (').
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Examples:
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format svcrdma: // many of the NFS/RDMA server dprintks
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format readahead // some dprintks in the readahead cache
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format nfsd:\040SETATTR // one way to match a format with whitespace
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format "nfsd: SETATTR" // a neater way to match a format with whitespace
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format 'nfsd: SETATTR' // yet another way to match a format with whitespace
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2009-02-05 23:53:15 +07:00
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line
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The given line number or range of line numbers is compared
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against the line number of each dprintk() callsite. A single
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line number matches the callsite line number exactly. A
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range of line numbers matches any callsite between the first
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and last line number inclusive. An empty first number means
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the first line in the file, an empty line number means the
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last number in the file. Examples:
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line 1603 // exactly line 1603
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line 1600-1605 // the six lines from line 1600 to line 1605
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line -1605 // the 1605 lines from line 1 to line 1605
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line 1600- // all lines from line 1600 to the end of the file
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The flags specification comprises a change operation followed
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by one or more flag characters. The change operation is one
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of the characters:
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-
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remove the given flags
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+
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add the given flags
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=
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set the flags to the given flags
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The flags are:
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2011-01-23 23:17:24 +07:00
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f
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Include the function name in the printed message
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l
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Include line number in the printed message
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m
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Include module name in the printed message
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2009-02-05 23:53:15 +07:00
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p
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Causes a printk() message to be emitted to dmesg
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2011-01-23 23:17:24 +07:00
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t
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Include thread ID in messages not generated from interrupt context
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2009-02-05 23:53:15 +07:00
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2011-01-23 23:17:24 +07:00
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Note the regexp ^[-+=][flmpt]+$ matches a flags specification.
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2009-02-05 23:53:15 +07:00
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Note also that there is no convenient syntax to remove all
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2011-01-23 23:17:24 +07:00
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the flags at once, you need to use "-flmpt".
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2009-02-05 23:53:15 +07:00
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2010-08-06 21:11:02 +07:00
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Debug messages during boot process
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==================================
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To be able to activate debug messages during the boot process,
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even before userspace and debugfs exists, use the boot parameter:
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ddebug_query="QUERY"
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QUERY follows the syntax described above, but must not exceed 1023
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characters. The enablement of debug messages is done as an arch_initcall.
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Thus you can enable debug messages in all code processed after this
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arch_initcall via this boot parameter.
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On an x86 system for example ACPI enablement is a subsys_initcall and
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ddebug_query="file ec.c +p"
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will show early Embedded Controller transactions during ACPI setup if
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your machine (typically a laptop) has an Embedded Controller.
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PCI (or other devices) initialization also is a hot candidate for using
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this boot parameter for debugging purposes.
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2009-02-05 23:53:15 +07:00
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Examples
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========
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// enable the message at line 1603 of file svcsock.c
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nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
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<debugfs>/dynamic_debug/control
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// enable all the messages in file svcsock.c
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nullarbor:~ # echo -n 'file svcsock.c +p' >
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<debugfs>/dynamic_debug/control
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// enable all the messages in the NFS server module
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|
nullarbor:~ # echo -n 'module nfsd +p' >
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<debugfs>/dynamic_debug/control
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// enable all 12 messages in the function svc_process()
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|
nullarbor:~ # echo -n 'func svc_process +p' >
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<debugfs>/dynamic_debug/control
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|
// disable all 12 messages in the function svc_process()
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|
nullarbor:~ # echo -n 'func svc_process -p' >
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<debugfs>/dynamic_debug/control
|
2009-02-06 08:54:26 +07:00
|
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|
// enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
|
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|
|
nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
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|
<debugfs>/dynamic_debug/control
|