Items

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An item is a collection of tags that together describe a hardware component.

hwi_item tag

The first tag in each item always begins with the hwi_item structure (which, like other tags, must start with the hwi_prefix structure):

struct hwi_item {
    struct hwi_prefix   prefix;
    uint16_t            itemsize;
    uint16_t            itemname;
    uint16_t            owner;
    uint16_t            kids;
};

itemsize: The distance, in 4-byte quantities, to the start of the next item tag.
itemname: An offset into the strings section of the system page for the name of the item being described.; This field differs from the prefix.name field, which specifies the type of structure that stores the hwi_item tag.
owner: The offset, in bytes, from the start of the hwinfo section to the item that owns this item.; This field is used to group items into a tree structure, similar to a filesystem directory hierarchy. For a root item in an ownership tree, the field is set to HWI_NULL_OFF.
kids: The number children of the current item.

Group item

The Group item is implemented by the hwi_group structure and is used to group items together. It serves the same purpose as a directory in a filesystem (e.g., for the devclass level of the /hw tree).

#define HWI_TAG_NAME_group  "Group"
#define HWI_TAG_ALIGN_group (sizeof(uint32_t))

struct hwi_group {
    struct hwi_item     item;
};

item: The item.

Bus item

The Bus item is implemented by the hwi_bus structure and tells the system about a hardware bus.

#define HWI_TAG_NAME_bus    "Bus"
#define HWI_TAG_ALIGN_bus   (sizeof(uint32))

struct hwi_bus {
    struct hwi_item     item;
};

item: The item.

Item names can be (but are not limited to):

#define HWI_ITEM_BUS_PCI        "pci"
#define HWI_ITEM_BUS_ISA        "isa"
#define HWI_ITEM_BUS_EISA       "eisa"
#define HWI_ITEM_BUS_MCA        "mca"
#define HWI_ITEM_BUS_PCMCIA     "pcmcia"
#define HWI_ITEM_BUS_CAN        "can"
#define HWI_ITEM_BUS_SDIO       "sdio"
#define HWI_ITEM_BUS_I394       "I394"
#define HWI_ITEM_BUS_MOST       "most"
#define HWI_ITEM_BUS_UNKNOWN    "unknown"

Device item

The Device item is implemented by the hwi_device structure and tells the system about an individual device (which is stored at the device level of the /hw tree).

#define HWI_TAG_NAME_device     "Device"
#define HWI_TAG_ALIGN_device    (sizeof(uint32))

struct hwi_device {
    struct hwi_item     item;
    uint32_t            pnpid;
};

item: The item.
pnpid: (Deprecated) The Plug and Play device identifier assigned by Microsoft. Only relevant for devices that play media.

Note:

Device items include hypervisor devices:

#define HWI_ITEM_DEVCLASS_QVM	"qvm"

Page updated: March 05, 2025