new_unrhdrdelete_unrhdralloc_unrfree_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.
Fn new_unrhdr low high mutex
Initialize a new unit number allocator entity.
The
Fa low
and
Fa 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
Fa mutex
is not
NULL
it is used for locking when allocating and freeing units.
Otherwise, internal mutex is used.
Fn delete_unrhdr uh
Destroy specified unit number allocator entity.
Fn 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.
Fn alloc_unrl uh
Same as
alloc_unr ();
except that mutex is assumed to be already locked and thus is not used.
Fn free_unr uh
Free a previously allocated unit number.
This function 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
Fx 6.0 .
AUTHORS
An -nosplit
Kernel unit number allocator was written by
An Poul-Henning Kamp .
This manpage was written by
An Gleb Smirnoff .
