sysfs-firmware-dmi-entries (4328B)
1What: /sys/firmware/dmi/entries/ 2Date: February 2011 3Contact: Mike Waychison <mikew@google.com> 4Description: 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. 9 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. 14 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. 20 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. 26 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)": 35 36 Example entry directories:: 37 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 ... 43 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. 49 50 Each DMI entry in sysfs has the common header values 51 exported as attributes: 52 53 ======== ================================================= 54 handle The 16bit 'handle' that is assigned to this 55 entry by the firmware. This handle may be 56 referred to by other entries. 57 length The length of the entry, as presented in the 58 entry itself. Note that this is _not the 59 total count of bytes associated with the 60 entry. This value represents the length of 61 the "formatted" portion of the entry. This 62 "formatted" region is sometimes followed by 63 the "unformatted" region composed of nul 64 terminated strings, with termination signalled 65 by a two nul characters in series. 66 raw The raw bytes of the entry. This includes the 67 "formatted" portion of the entry, the 68 "unformatted" strings portion of the entry, 69 and the two terminating nul characters. 70 type The type of the entry. This value is the same 71 as found in the directory name. It indicates 72 how the rest of the entry should be interpreted. 73 instance The instance ordinal of the entry for the 74 given type. This value is the same as found 75 in the parent directory name. 76 position The ordinal position (zero-based) of the entry 77 within the entirety of the DMI entry table. 78 ======== ================================================= 79 80 **Entry Specialization** 81 82 Some entry types may have other information available in 83 sysfs. Not all types are specialized. 84 85 **Type 15 - System Event Log** 86 87 This entry allows the firmware to export a log of 88 events the system has taken. This information is 89 typically backed by nvram, but the implementation 90 details are abstracted by this table. This entry's data 91 is exported in the directory:: 92 93 /sys/firmware/dmi/entries/15-0/system_event_log 94 95 and has the following attributes (documented in the 96 SMBIOS / DMI specification under "System Event Log (Type 15)": 97 98 - area_length 99 - header_start_offset 100 - data_start_offset 101 - access_method 102 - status 103 - change_token 104 - access_method_address 105 - header_format 106 - per_log_type_descriptor_length 107 - type_descriptors_supported_count 108 109 As well, the kernel exports the binary attribute: 110 111 ============= ==================================== 112 raw_event_log The raw binary bits of the event log 113 as described by the DMI entry. 114 ============= ====================================