alloc_unr(9)

NAME

new_unrhdr, delete_unrhdr, alloc_unr, free_unr - kernel unit

number allocator

SYNOPSIS

#include <sys/systm.h>
struct unrhdr *
new_unrhdr(int low, int high, struct mtx *mutex);
void
delete_unrhdr(struct unrhdr *uh);
int
alloc_unr(struct unrhdr *uh);
int
alloc_unrl(struct unrhdr *uh);
void
free_unr(struct unrhdr *uh, u_int item);

DESCRIPTION

The kernel unit number allocator is a generic facility,

which allows to
allocate unit numbers within a specified range.

new_unrhdr(low, high, mutex)

Initialize a new unit number allocator entity. The

low and high
arguments specify minimum and maximum number of unit

numbers.
There is no cost associated with the range of unit

numbers, so
unless the resource really is finite, INT_MAX can be

used. If
mutex is not NULL, it is used for locking when allo

cating and
freeing units. Otherwise, internal mutex is used.

delete_unrhdr(uh)

Destroy specified unit number allocator entity.

alloc_unr(uh)

Return a new unit number. The lowest free number is

always allocated. This function does not allocate memory and

never sleeps,
however it may block on a mutex. If no free unit

numbers are
left, -1 is returned.

alloc_unrl(uh)

Same as alloc_unr() except that mutex is assumed to

be already
locked and thus is not used.

free_unr(uh)

Free a previously allocated unit number. This func

tion may
require allocating memory, and thus it can sleep.

There is no
pre-locked variant.

CODE REFERENCES

The above functions are implemented in sys/kern/subr_unit.c.

HISTORY

Kernel unit number allocator first appeared in FreeBSD 6.0.

AUTHORS

Kernel unit number allocator was written by Poul-Henning

Kamp. This manpage was written by Gleb Smirnoff.

BSD March 23, 2005

BSD