---
name: "bus_alloc_resource"
section: "9"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/bus_alloc_resource"
---

# bus\_alloc\_resource(9)

allocate resources from a parent bus

## NAME

**bus\_alloc\_resource**, **bus\_alloc\_resource\_any**, **bus\_alloc\_resource\_anywhere** – allocate resources from a parent bus

## SYNOPSIS

**#include \<sys/param.h\>**

**#include \<sys/bus.h\>**

**#include \<machine/bus.h\>**

**#include \<sys/rman.h\>**

**#include \<machine/resource.h\>**

*struct* *resource* *\**\

**bus\_alloc\_resource**(*device\_t dev*, *int type*, *int rid*, *rman\_res\_t start*, *rman\_res\_t end*, *rman\_res\_t count*, *u\_int flags*);

*struct* *resource* *\**\

**bus\_alloc\_resource\_any**(*device\_t dev*, *int type*, *int rid*, *u\_int flags*);

*struct* *resource* *\**\

**bus\_alloc\_resource\_anywhere**(*device\_t dev*, *int type*, *int rid*, *rman\_res\_t count*, *u\_int flags*);

## DESCRIPTION

This is an easy interface to the resource-management functions. It hides the indirection through the parent's method table. This function generally should be called in attach, but (except in some rare cases) never earlier.

The **bus\_alloc\_resource\_any**() and **bus\_alloc\_resource\_anywhere**() functions are convenience wrappers for **bus\_alloc\_resource**(). **bus\_alloc\_resource\_any**() sets *start*, *end*, and *count* to the default resource (see description of *start* below). **bus\_alloc\_resource\_anywhere**() sets *start* and *end* to the default resource and uses the provided *count* argument.

The arguments are as follows:

-

  *dev* is the device that requests ownership of the resource. Before allocation, the resource is owned by the parent bus.

-

  *type* is the type of resource you want to allocate. It is one of:

  - PCI\_RES\_BUS

    for PCI bus numbers

  - SYS\_RES\_IRQ

    for IRQs

  - SYS\_RES\_DRQ

    for ISA DMA lines

  - SYS\_RES\_IOPORT

    for I/O ports

  - SYS\_RES\_MEMORY

    for I/O memory

-

  *rid* is a bus specific handle that identifies the resource being allocated. For ISA this is an index into an array of resources that have been setup for this device by either the PnP mechanism, or via the hints mechanism. For PCCARD, this is an index into the array of resources described by the PC Card's CIS entry. For PCI, the offset into PCI config space which has the BAR to use to access the resource.

-

  *start* and *end* are the start/end addresses of the resource. If you specify values of 0ul for *start* and ~0ul for *end* and 1 for *count*, the default values for the bus are calculated.

-

  *count* is the size of the resource. For example, the size of an I/O port is usually 1 byte (but some devices override this). If you specified the default values for *start* and *end*, then the default value of the bus is used if *count* is smaller than the default value and *count* is used, if it is bigger than the default value.

-

  *flags* sets the flags for the resource. You can set zero or more of these flags:

  - RF\_ACTIVE

    activate resource atomically.

  - RF\_PREFETCHABLE

    resource is prefetchable.

  - RF\_SHAREABLE

    resource permits contemporaneous sharing. It should always be set unless you know that the resource cannot be shared. It is the bus driver's task to filter out the flag if the bus does not support sharing.

  - RF\_UNMAPPED

    do not establish implicit mapping when activated via [bus\_activate\_resource(9)](/bus_activate_resource/9.md).

## RETURN VALUES

A pointer to *struct* *resource* is returned on success, a null pointer otherwise.

## EXAMPLES

This is some example code that allocates a 32 byte I/O port range and an IRQ.

```
	struct resource *portres, *irqres;
	portres = bus_alloc_resource(dev, SYS_RES_IOPORT, 0,
			0ul, ~0ul, 32, RF_ACTIVE);
	irqres = bus_alloc_resource_any(dev, SYS_RES_IRQ, 0,
			RF_ACTIVE | RF_SHAREABLE);
```

## SEE ALSO

[bus\_activate\_resource(9)](/bus_activate_resource/9.md), [bus\_adjust\_resource(9)](/bus_adjust_resource/9.md), [bus\_map\_resource(9)](/bus_map_resource/9.md), [bus\_release\_resource(9)](/bus_release_resource/9.md), [device(9)](/device/9.md), [driver(9)](/driver/9.md)

## AUTHORS

This manual page was written by Alexander Langer ⟨*alex@big.endian.de*⟩ with parts by Warner Losh ⟨*imp@FreeBSD.org*⟩.