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Based on kernel version 4.1. Page generated on 2015-06-28 12:07 EST.

1	What:		/sys/firmware/dmi/
2	Date:		February 2011
3	Contact:	Mike Waychison <mikew@google.com>
4	Description:
5			Many machines' firmware (x86 and ia64) export DMI /
6			SMBIOS tables to the operating system.  Getting at this
7			information is often valuable to userland, especially in
8			cases where there are OEM extensions used.
10			The kernel itself does not rely on the majority of the
11			information in these tables being correct.  It equally
12			cannot ensure that the data as exported to userland is
13			without error either.
15			DMI is structured as a large table of entries, where
16			each entry has a common header indicating the type and
17			length of the entry, as well as a firmware-provided
18			'handle' that is supposed to be unique amongst all
19			entries.
21			Some entries are required by the specification, but many
22			others are optional.  In general though, users should
23			never expect to find a specific entry type on their
24			system unless they know for certain what their firmware
25			is doing.  Machine to machine experiences will vary.
27			Multiple entries of the same type are allowed.  In order
28			to handle these duplicate entry types, each entry is
29			assigned by the operating system an 'instance', which is
30			derived from an entry type's ordinal position.  That is
31			to say, if there are 'N' multiple entries with the same type
32			'T' in the DMI tables (adjacent or spread apart, it
33			doesn't matter), they will be represented in sysfs as
34			entries "T-0" through "T-(N-1)":
36			Example entry directories:
38				/sys/firmware/dmi/entries/17-0
39				/sys/firmware/dmi/entries/17-1
40				/sys/firmware/dmi/entries/17-2
41				/sys/firmware/dmi/entries/17-3
42				...
44			Instance numbers are used in lieu of the firmware
45			assigned entry handles as the kernel itself makes no
46			guarantees that handles as exported are unique, and
47			there are likely firmware images that get this wrong in
48			the wild.
50			Each DMI entry in sysfs has the common header values
51			exported as attributes:
53			handle	: The 16bit 'handle' that is assigned to this
54				  entry by the firmware.  This handle may be
55				  referred to by other entries.
56			length	: The length of the entry, as presented in the
57				  entry itself.  Note that this is _not the
58				  total count of bytes associated with the
59				  entry_.  This value represents the length of
60				  the "formatted" portion of the entry.  This
61				  "formatted" region is sometimes followed by
62				  the "unformatted" region composed of nul
63				  terminated strings, with termination signalled
64				  by a two nul characters in series.
65			raw	: The raw bytes of the entry. This includes the
66				  "formatted" portion of the entry, the
67				  "unformatted" strings portion of the entry,
68				  and the two terminating nul characters.
69			type	: The type of the entry.  This value is the same
70				  as found in the directory name.  It indicates
71				  how the rest of the entry should be interpreted.
72			instance: The instance ordinal of the entry for the
73				  given type.  This value is the same as found
74				  in the parent directory name.
75			position: The ordinal position (zero-based) of the entry
76				  within the entirety of the DMI entry table.
78			=== Entry Specialization ===
80			Some entry types may have other information available in
81			sysfs.  Not all types are specialized.
83			--- Type 15 - System Event Log ---
85			This entry allows the firmware to export a log of
86			events the system has taken.  This information is
87			typically backed by nvram, but the implementation
88			details are abstracted by this table.  This entry's data
89			is exported in the directory:
91			/sys/firmware/dmi/entries/15-0/system_event_log
93			and has the following attributes (documented in the
94			SMBIOS / DMI specification under "System Event Log (Type 15)":
96			area_length
97			header_start_offset
98			data_start_offset
99			access_method
100			status
101			change_token
102			access_method_address
103			header_format
104			per_log_type_descriptor_length
105			type_descriptors_supported_count
107			As well, the kernel exports the binary attribute:
109			raw_event_log	: The raw binary bits of the event log
110					  as described by the DMI entry.
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