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Date: Tue, 28 Jun 2011 01:09:52 -0600 From: Jim Cromie <jim.cromie@...il.com> To: linux-kernel@...r.kernel.org Cc: gnb@...h.org, jbaron@...hat.com, bvanassche@....org, gregkh@...e.de, Jim Cromie <jim.cromie@...il.com> Subject: [PATCH 11/11] dynamic_debug: document use of pendinq queries at boot-time Add paragraph that pendinq-queries are checked when modules are loaded, so debug statements can be used in module_init functions. Signed-off-by: Jim Cromie <jim.cromie@...il.com> --- Documentation/dynamic-debug-howto.txt | 20 ++++++++++++++------ 1 files changed, 14 insertions(+), 6 deletions(-) diff --git a/Documentation/dynamic-debug-howto.txt b/Documentation/dynamic-debug-howto.txt index d0faf98..49b75b81 100644 --- a/Documentation/dynamic-debug-howto.txt +++ b/Documentation/dynamic-debug-howto.txt @@ -120,11 +120,12 @@ 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() +The match-specs 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. +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 is legal but +pointless, it will not match any debug statement callsites. A match specification comprises a keyword, which controls the attribute of the callsite to be compared, and a value to compare against. Possible @@ -242,13 +243,20 @@ 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 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. +You can also give queries for modules which are not yet loaded, but +will be, via udev or /etc/modules. These queries are saved to a +pending-queries list, and are applied when the module is loaded, and +before the module's init function is invoked. Note that modules which +have no debug messages do not trigger this, so queries for them will +remain on the pending-list until reboot. Examples ======== -- 1.7.4.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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