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authorEduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>2008-08-10 20:14:04 +0300
committerPekka Enberg <penberg@cs.helsinki.fi>2008-12-29 15:34:02 +0200
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kmemtrace: Additional documentation.
Documented kmemtrace's ABI, purpose and design. Also includes a short usage guide, FAQ, as well as a link to the userspace application's Git repository, which is currently hosted at repo.or.cz. Signed-off-by: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro> Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
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+What: /sys/kernel/debug/kmemtrace/
+Date: July 2008
+Contact: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
+Description:
+
+In kmemtrace-enabled kernels, the following files are created:
+
+/sys/kernel/debug/kmemtrace/
+ cpu<n> (0400) Per-CPU tracing data, see below. (binary)
+ total_overruns (0400) Total number of bytes which were dropped from
+ cpu<n> files because of full buffer condition,
+ non-binary. (text)
+ abi_version (0400) Kernel's kmemtrace ABI version. (text)
+
+Each per-CPU file should be read according to the relay interface. That is,
+the reader should set affinity to that specific CPU and, as currently done by
+the userspace application (though there are other methods), use poll() with
+an infinite timeout before every read(). Otherwise, erroneous data may be
+read. The binary data has the following _core_ format:
+
+ Event ID (1 byte) Unsigned integer, one of:
+ 0 - represents an allocation (KMEMTRACE_EVENT_ALLOC)
+ 1 - represents a freeing of previously allocated memory
+ (KMEMTRACE_EVENT_FREE)
+ Type ID (1 byte) Unsigned integer, one of:
+ 0 - this is a kmalloc() / kfree()
+ 1 - this is a kmem_cache_alloc() / kmem_cache_free()
+ 2 - this is a __get_free_pages() et al.
+ Event size (2 bytes) Unsigned integer representing the
+ size of this event. Used to extend
+ kmemtrace. Discard the bytes you
+ don't know about.
+ Sequence number (4 bytes) Signed integer used to reorder data
+ logged on SMP machines. Wraparound
+ must be taken into account, although
+ it is unlikely.
+ Caller address (8 bytes) Return address to the caller.
+ Pointer to mem (8 bytes) Pointer to target memory area. Can be
+ NULL, but not all such calls might be
+ recorded.
+
+In case of KMEMTRACE_EVENT_ALLOC events, the next fields follow:
+
+ Requested bytes (8 bytes) Total number of requested bytes,
+ unsigned, must not be zero.
+ Allocated bytes (8 bytes) Total number of actually allocated
+ bytes, unsigned, must not be lower
+ than requested bytes.
+ Requested flags (4 bytes) GFP flags supplied by the caller.
+ Target CPU (4 bytes) Signed integer, valid for event id 1.
+ If equal to -1, target CPU is the same
+ as origin CPU, but the reverse might
+ not be true.
+
+The data is made available in the same endianness the machine has.
+
+Other event ids and type ids may be defined and added. Other fields may be
+added by increasing event size, but see below for details.
+Every modification to the ABI, including new id definitions, are followed
+by bumping the ABI version by one.
+
+Adding new data to the packet (features) is done at the end of the mandatory
+data:
+ Feature size (2 byte)
+ Feature ID (1 byte)
+ Feature data (Feature size - 4 bytes)
+
+
+Users:
+ kmemtrace-user - git://repo.or.cz/kmemtrace-user.git
+