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