man/man9p/size.9p

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 SIZE 9P "June 20, 2021"
 NAME
size, Nblock, blksize, device-nblocks, device-blksize - device size properties
 DESCRIPTION
A driver can communicate size information to the system by the values
associated with following properties. Size information falls into two
categories: device size associated with a dev_info_t node, and minor node
size associated with a ddi_create_minor_node(9F) dev_t (partition).

device size property names:
device-nblocks

An int64_t property representing device size in
device-blksize blocks.


device-blksize

An integer property representing the size in bytes of a block. If defined, the
value must be a power of two. If not defined, DEV_BSIZE is implied.


minor size property names:
Size

An int64_t property representing the size in bytes of a character minor
device (S_IFCHR spec_type in ddi_create_minor_node).


Nblocks

An int64_t property representing the number blocks, in
device-blksize units, of a block minor device (S_IFBLK
spec_type in ddi_create_minor_node).


blksize

An integer property representing the size in bytes of a block. If defined, the
value must be a power of two. If not defined, DEV_BSIZE is implied.


A driver that implements both block and character minor device nodes should
support both "Size" and "Nblocks". Typically, the following is true: Size =
Nblocks * blksize.

A driver where all ddi_create_minor_node(9F) calls for a given instance are
associated with the same physical block device should implement
"device-nblocks". If the device has a fixed block size with a value other
than DEV_BSIZE then "device-blksize" should be implemented.

The driver is responsible for ensuring that property values are updated when
device, media, or partition sizes change. For each represented item, if its
size is know to be zero, the property value should be zero. If its size is
unknown, the property should not be defined.

A driver may choose to implement size properties within its prop_op(9E)
implementation. This reduces system memory since no space is used to store the
properties.

The DDI property interfaces deal in signed numbers. All size(9P) values should
be considered unsigned. It is the responsibility of the code dealing with the
property value to ensure that an unsigned interpretation occurs.
 ATTRIBUTES
See attributes(7) for descriptions of the following attributes:


ATTRIBUTE TYPE ATTRIBUTE VALUE
Interface Stability Committed


 SEE ALSO
attach(9E), detach(9E), prop_op(9E), ddi_create_minor_node(9F),
inquiry-vendor-id(9P)

Writing Device Drivers