forked from luck/tmp_suning_uos_patched
239a5791ff
With the realization that having debugfs enabled on "production" systems is generally not a good idea, debugfs is being disabled from more and more platforms over time. However, the functionality of dynamic debugging still is needed at times, and since it relies on debugfs for its user api, having debugfs disabled also forces dynamic debug to be disabled. To get around this, also create the "control" file for dynamic_debug in procfs. This allows people turn on debugging as needed at runtime for individual driverfs and subsystems. Reported-by: many different companies Cc: Jason Baron <jbaron@akamai.com> Acked-by: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20200210211142.GB1373304@kroah.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
357 lines
13 KiB
ReStructuredText
357 lines
13 KiB
ReStructuredText
Dynamic debug
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+++++++++++++
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Introduction
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============
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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
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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()`` and
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``print_hex_dump_debug()``/``print_hex_dump_bytes()`` calls can be dynamically
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enabled per-callsite.
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If ``CONFIG_DYNAMIC_DEBUG`` is not set, ``print_hex_dump_debug()`` is just
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shortcut for ``print_hex_dump(KERN_DEBUG)``.
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For ``print_hex_dump_debug()``/``print_hex_dump_bytes()``, format string is
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its ``prefix_str`` argument, if it is constant string; or ``hexdump``
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in case ``prefix_str`` is built dynamically.
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Dynamic debug has even more useful features:
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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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- 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``
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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()`` are controlled via writing to a
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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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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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Note, for systems without 'debugfs' enabled, the control file can be
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found in ``/proc/dynamic_debug/control``.
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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
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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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...
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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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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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# 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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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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by spaces or tabs. So these are all equivalent::
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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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nullarbor:~ # echo -n ' 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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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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~# echo "func pnpacpi_get_resources +p; func pnp_assign_mem +p" \
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> <debugfs>/dynamic_debug/control
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If your query set is big, you can batch them too::
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~# cat query-batch-file > <debugfs>/dynamic_debug/control
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Another way is to use wildcards. The match rule supports ``*`` (matches
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zero or more characters) and ``?`` (matches exactly one character). For
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example, you can match all usb drivers::
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~# echo "file drivers/usb/* +p" > <debugfs>/dynamic_debug/control
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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 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 will select all debug statement callsites.
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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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'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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lineno ::= unsigned-int
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.. note::
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``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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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 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 ``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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the first line in the file, an empty last line number means the
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last line 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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- 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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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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For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only ``p`` flag
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have meaning, other flags ignored.
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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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==================================
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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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On an x86 system for example ACPI enablement is a subsys_initcall and::
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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. ``ddebug_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 doesn't 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 debugfs 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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::
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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
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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 messages in files of which the paths include string "usb"
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nullarbor:~ # echo -n '*usb* +p' > <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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