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    SubjectRe: [PATCH 23/26] dynamic_debug: document pending queries, flags-filter, multiple queries
    On 09/21/2011 02:55 PM, jim.cromie@gmail.com wrote:
    > From: Jim Cromie <jim.cromie@gmail.com>
    >
    > Rework description of flags-spec into 3 parts; flags-filter, flags-change,
    > flags-values. Add section on pending-queries. Explain flags filtering
    > in detail. Reflow some paragraphs.
    >
    > Add example of a command-file which shows commenting,
    > multiple queries per line, and describes constraints.
    >
    > Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
    > ---
    > Documentation/dynamic-debug-howto.txt | 336 ++++++++++++++++++++++-----------
    > 1 files changed, 222 insertions(+), 114 deletions(-)
    >
    > diff --git a/Documentation/dynamic-debug-howto.txt b/Documentation/dynamic-debug-howto.txt
    > index f959909..bf9037f 100644
    > --- a/Documentation/dynamic-debug-howto.txt
    > +++ b/Documentation/dynamic-debug-howto.txt
    > @@ -4,117 +4,134 @@ 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_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. If kernel is

    If {the | a} kernel is

    > +built with CONFIG_DYNAMIC_DEBUG=y, 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:
    > + * Simple query language allows turning on and off debugging statements
    > + by matching any combination of 0 or 1 of:
    >
    > - source filename
    > - function name
    > - line number (including ranges of line numbers)
    > - module name
    > - format string
    > + - current debugging flags
    >
    > - * 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:
    > +The behaviour of pr_debug()/dev_dbg()/net_dbg()s are controlled via

    The behaviour ... is controlled by

    > +writing to a control file in the 'debugfs' filesystem. Thus, you must
    > +first mount the debugfs filesystem, in order to make use of this

    drop comma.

    > +feature. Subsequently, we refer to mount point as $DBGFS, and the

    to the mount point
    also drop comma after $DBGFS.

    > +control file as $CONTROL. So 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
    > +nullarbor:~ # echo file svcsock.c line 1603 +p > $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
    > +nullarbor:~ # 'echo file svcsock.c wtf 1 +p' > $CONTROL
    > -bash: echo: write error: Invalid argument
    >
    > Viewing Dynamic Debug Behaviour
    > -===========================
    > +===============================
    >
    > -You can view the currently configured behaviour of all the debug statements
    > -via:
    > +You can view the currently configured behaviour by catting or grepping
    > +the $CONTROL file:
    >
    > -nullarbor:~ # cat <debugfs>/dynamic_debug/control
    > +root@voyage:~# grep freezer $CONTROL
    > +kernel/freezer.c:128 [freezer]cancel_freezing =_ " clean up: %s\012"
    > +kernel/freezer.c:60 [freezer]refrigerator =_ "%s left refrigerator\012"
    > +kernel/freezer.c:41 [freezer]refrigerator =_ "%s entered refrigerator\012"
    > +
    > +The third column shows the current flag settings for each debug

    There are columns there??!!?? Hard to tell.

    > +statement callsite (menmonic: what they are equal to, see below for

    mnemonic:

    > +definitions of the flags). The default value, with nothing enabled,
    > +is "=_". So you can view all the debug statement callsites with any
    > +non-default flags:
    > +
    > +nullarbor:~ # grep -v "=_" $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/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.
    >
    > -You can also apply standard Unix text manipulation filters to this
    > -data, e.g.
    > +nullarbor:~# echo file svcsock.c line 1603 +p > $CONTROL
    >
    > -nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control | wc -l
    > -62
    > +nullarbor:~# echo 'file svcsock.c line 1603 +p' > $CONTROL
    >
    > -nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control | wc -l
    > -42
    > +nullarbor:~# echo -n ' file svcsock.c line 1603 +p ' > $CONTROL
    >
    > -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:~# echo -n 'file svcsock.c line 1603 +p' > $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"
    > +Multiple query/commands
    > +=======================
    >
    > +Commands are bounded by a write() system call. Subject to this limit

    s/bounded/limited/ ?
    > +(or 1024 for boot-line parameter) you can send multiple commands,

    Maybe you could rewrite this paragraph so that I can understand what
    it means?

    > +separated by ';' or '\n'

    End sentence with period ('.').

    >
    > -Command Language Reference
    > -==========================
    > +voyage:~# echo "func cancel_freezing +p ; func refrigerator +p; " > $CONTROL
    > +voyage:~# printf "func cancel_freezing +p \n func refrigerator +p; " > $CONTROL
    >
    > -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:
    > +voyage:~# cat dyndbg-cmdfile
    >
    > -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
    > + # comments and blank lines ok, but cannot contain semicolon
    > + # multiple cmds per line, 1st must be terminated by semicolon

    Change "1st" to "all but last" ?

    > + func foo p=_ ; func buzz p=_
    > + func bar p=_ ; func bum p=_
    > + func yak p=_ ; # trailing comment, requires semicolon to terminate cmd
    >
    > -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:
    > + # heres the oddity: semicolon terminates comment, so this works
    > + func foo +p ; # comment ; func bar +p
    > + # allowing this keeps parsing simple
    >
    > -nullarbor:~ # echo 'file svcsock.c line 1603 +p' > /proc/dprintk ;\
    > -> echo 'file svcsock.c line 1563 +p' > /proc/dprintk
    > +voyage:~# cat dyndbg-cmdfile > $CONTROL
    > +dynamic_debug:ddebug_exec_queries: processed 7 queries, with 0 errs
    > +
    > +Multiple commands are processed independently, this allows you to send

    independently. This allows

    > +commands which may fail, for example if a module is not present. The
    > +last failing command returns its error.
    > +
    > +Or you can do an "echo" for each, like:
    > +
    > +nullarbor:~ # echo 'file svcsock.c line 1603 +p' > $CONTROL; \
    > +> echo 'file svcsock.c line 1563 +p' > $CONTROL
    >
    > or even like:
    >
    > nullarbor:~ # (
    > > echo 'file svcsock.c line 1603 +p' ;\
    > > echo 'file svcsock.c line 1563 +p' ;\
    > -> ) > /proc/dprintk
    > +> ) > $CONTROL
    >
    > -At the syntactical level, a command comprises a sequence of match
    > +Query/command syntax
    > +====================
    > +
    > +At the syntactic 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.
    > +The match-specs are used to choose a subset of the known callsites to
    > +which to apply the flags-spec. Think of them as a query with implicit
    > +ANDs between each pair. This means that multiple specs of a given
    > +type are nonsense; a module cannot match A and B simultaneously. Note
    > +that an empty list of match-specs matches all callsites.
    >
    > A match specification comprises a keyword, which controls the attribute
    > of the callsite to be compared, and a value to compare against. Possible
    > @@ -125,12 +142,13 @@ match-spec ::= 'func' string |
    > 'module' string |
    > 'format' string |
    > 'line' line-range
    > +// Note: no wildcards, regexs are accepted
    >
    > line-range ::= lineno |
    > '-'lineno |
    > lineno'-' |
    > lineno'-'lineno
    > -// Note: line-range cannot contain space, e.g.
    > +// Note: line-range cannot contain a space, e.g.
    > // "1-30" is valid range but "1 - 30" is not.
    >
    > lineno ::= unsigned-int
    > @@ -144,11 +162,12 @@ func
    > 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:
    > + The given string is compared against either the full pathname,
    > + relative path from kernel source dir, or the basename of the
    > + source file of each callsite. Examples:
    >
    > file svcsock.c
    > + file kernel/freezer.c
    > file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c
    >
    > module
    > @@ -157,7 +176,7 @@ module
    > seen in "lsmod", i.e. without the directory or the .ko
    > suffix and with '-' changed to '_'. Examples:
    >
    > - module sunrpc
    > + module ide_pci_generic
    > module nfsd
    >
    > format
    > @@ -190,79 +209,168 @@ line
    > 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
    > +flags specification
    > +===================
    >
    > -=
    > - set the flags to the given flags
    > +The flags specification matches the regexp: ^[flmpta_]*[-+=][flmpta_]*$
    > +and has 3 parts:
    >
    > -The flags are:
    > +flags filter (optional):
    > + The filter precedes the operation [-+=], and constrains matching
    > + to thoses callsite with given flags set. This allows altering

    those

    > + flags on callsites with filtered flag values
    >
    > -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
    > + pm+t # add t to enabled sites which have m
    > + p+t # add t to all enabled sites, both m and !m
    > + tmf-p # disable sites with 'tmf'
    > + tmf+p # re-enable those disabled sites
    >
    > -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".
    > +flags change operation:
    > + '-' 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

    to the kernel log (or kernel log buffer);

    [dmesg is a program that can print the kernel log.]

    > + other flags can thus be left on, and used in filters.
    > + 'm' Include module name in the printed message
    > + 'f' Include the function name in the printed message
    > + 'l' Include line number in the printed message
    > + 't' Include thread ID in messages not generated from interrupt context
    > + 'a' Also add query to pending queries, for later (re)application
    > + '_' default/null flag.
    > + Primarily for display, so grep "=_" can avoid " = " in format strings.
    > + Also usable (but not required) to clear all flags.
    > +
    > +Pending queries
    > +===============
    > +
    > +Queries submitted with 'a' are applied to current callsites as above,
    > +but are also added to a pending list. When a module is loaded later,
    > +pending queries are applied to the module in the order given.
    > +
    > +This is done before the module_init() routine is run, so pr_debug()s
    > +can be active during initialization. To better support module
    > +debugging, pending queries remain on the list through modprobe-rmmod
    > +cycles.
    > +
    > +You can review currently pending queries by catting or grepping
    > +$DEBUFS/dynamic_debug/pending. To simplify removal via

    $DBGFS ?

    > +cut-paste-edit, its format is similar to the query syntax:
    > +
    > + root@voyage:~# cat /dbg/dynamic_debug/pending

    use $DBGFS in path name?

    > + # func file module format line flags mask
    > + ...
    > + func a299 line 0-0 =pa
    > + func a300 line 0-0 =pa
    > +
    > +To remove a pending query, resubmit it with 'a' in filter-spec
    > +and zeroed flag-specs:
    > +
    > + # a simple helper shell-function, to shorten examples
    > + DBGFS=${DBGFS:=/dbg}
    > + CONTROL=$DBGFS/dynamic_debug/control
    > + function dbg_query() {
    > + echo "$*" > $CONTROL
    > + # see relevant settings, effects of the query/command
    > + grep $2 $DBGFS/dynamic_debug/*
    > + }
    > +
    > + voyage:~# dbg_query module foo +apt # original pending query
    > + voyage:~# dbg_query module foo a= # zero 'a' flag to remove query
    > + voyage:~# dbg_query module foo a-a # zero 'a', remove query
    > + voyage:~# dbg_query module foo a-ap # zero 'a', also disable callsites
    > +
    > +Deleting or altering a pending query requires an exact match on most
    > +of the match-spec; the same string specs must be given, but 'line 0-0'
    > +matches with '' and vice-versa. The filter-spec is ignored for
    > +pending-list changes.
    > +
    > + voyage:~# dbg_query module foo +apt # add PQ-1 before each of following..

    Sorry, I guess I'm dense today. What is this "PQ-1"?

    > +
    > + # will not remove PQ-1 (mismatch on lines)
    > + voyage:~# dbg_query module foo line 100-200 ap=
    > +
    > + # removes PQ-1 (exact match with PQ-1), disables active callsites (if any)
    > + voyage:~# dbg_query module foo line 0-0 ap=
    > +
    > + # delete PQ-1, leave callsites active (none of 'ptmfl' subtracted)
    > + voyage:~# dbg_query module foo a-a
    > +
    > + # delete PQ-1, disable callsites (all flags zeroed)
    > + voyage:~# dbg_query module foo a=_
    > +
    > + # delete PQ-1, leave callsites active (no 'm' on active callsites)
    > + voyage:~# dbg_query module foo am=_
    > +
    > + # del PQ-1, and disable callsites (-p), leaving 't'
    > + voyage:~# dbg_query module foo a-ap
    > +
    > + # del PQ-1, disable and clear callsites (-pt removes flags set by PQ-1)
    > + voyage:~# dbg_query module foo a-apt
    > +
    > + # del PQ-1, disable callsites with 'pt', leave 't'
    > + voyage:~# dbg_query module foo apt-ap
    > +
    > + # reactivate foo's callsites marked with 't' (see "flags filter" above)
    > + voyage:~# dbg_query module foo t+p
    > +
    > + # add 'm' to foo's callsites with 't', add new pending query with 'pm'
    > + voyage:~# dbg_query module foo at+pm
    > +
    > +Altering a pending query ('a' in filter) will also alter the callsites
    > +that it applies to (subject to filter match), but changing the active
    > +callsites (using a query without the 'a') does not change the pending
    > +query that applied it.
    >
    > 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 be able to activate debug messages during the boot process, even
    > +before userspace and debugfs exists, use the boot parameter:
    > +ddebug_query="QUERY".
    >
    > 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
    > +characters. It may contain multiple commands separated by ';'
    > +('\n' seems to be eaten by my bootloader).
    > +
    > +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"
    > +
    > +On an x86 system for example ACPI enablement is a subsys_initcall, so
    > + ddebug_query="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.
    >
    > -
    > Examples
    > ========
    >
    > // enable the message at line 1603 of file svcsock.c
    > -nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
    > - <debugfs>/dynamic_debug/control
    > +nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > $CONTROL
    >
    > // enable all the messages in file svcsock.c
    > -nullarbor:~ # echo -n 'file svcsock.c +p' >
    > - <debugfs>/dynamic_debug/control
    > +nullarbor:~ # echo -n 'file svcsock.c +p' > $CONTROL
    >
    > // enable all the messages in the NFS server module
    > -nullarbor:~ # echo -n 'module nfsd +p' >
    > - <debugfs>/dynamic_debug/control
    > +nullarbor:~ # echo -n 'module nfsd +p' > $CONTROL
    >
    > // enable all 12 messages in the function svc_process()
    > -nullarbor:~ # echo -n 'func svc_process +p' >
    > - <debugfs>/dynamic_debug/control
    > +nullarbor:~ # echo -n 'func svc_process +p' > $CONTROL
    >
    > // disable all 12 messages in the function svc_process()
    > -nullarbor:~ # echo -n 'func svc_process -p' >
    > - <debugfs>/dynamic_debug/control
    > +nullarbor:~ # echo -n 'func svc_process -p' > $CONTROL
    >
    > // enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
    > -nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
    > - <debugfs>/dynamic_debug/control
    > +nullarbor:~ # echo -n 'format "nfsd: READ" +p' > $CONTROL
    > +
    > +// send query-command file to control
    > +root@voyage:~# cat dyndbg-cmdfile > $CONTROL
    > +dynamic_debug:ddebug_proc_open: called
    > +dynamic_debug:ddebug_proc_write: read 500 bytes from userspace
    > +dynamic_debug:ddebug_exec_queries: query 0: "func foo p=_ "
    > +dynamic_debug:ddebug_tokenize: split into words: "func" "foo" "p=_"
    > +dynamic_debug:ddebug_parse_query: parsed func="foo" file="" module="" format="" lineno=0-0
    > +...



    thanks,
    --
    ~Randy
    *** Remember to use Documentation/SubmitChecklist when testing your code ***


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