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UNR(9) FreeBSD Kernel Developer's Manual UNR(9)
NAME
new_unrhdr, clean_unrhdr, clear_unrhdr, delete_unrhdr, alloc_unr,
alloc_unr_specific, free_unr, create_iter_unr, next_iter_unr,
free_iter_unr - kernel unit number allocator
SYNOPSIS
#include <sys/systm.h>
struct unrhdr *
new_unrhdr(int low, int high, struct mtx *mutex);
void
clean_unrhdr(struct unrhdr *uh);
void
clean_unrhdrl(struct unrhdr *uh);
void
clear_unrhdr(struct unrhdr *uh);
void
delete_unrhdr(struct unrhdr *uh);
int
alloc_unr(struct unrhdr *uh);
int
alloc_unrl(struct unrhdr *uh);
int
alloc_unr_specific(struct unrhdr *uh, u_int item);
void
free_unr(struct unrhdr *uh, u_int item);
void *
create_iter_unr(struct unrhdr *uh);
int
next_iter_unr(void *handle);
void
free_iter_unr(void *handle);
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 allocating and
freeing units. If the passed value is the token UNR_NO_MTX, then
no locking is applied internally. Otherwise, internal mutex is
used.
Delete specified unit number allocator entity. This function
frees the memory associated with the entity, it does not free any
units. To free all units use clear_unrhdr().
clean_unrhdr(uh)
Freeing unit numbers might result in some internal memory
becoming unused. There are unit allocator consumers that cannot
tolerate taking malloc(9) locks to free the memory, while having
their unit mutex locked. For this reason, free of the unused
memory after delete is postponed until the consumer can afford
calling into the malloc(9) subsystem. Call clean_unrhdr(uh) to
do the cleanup. In particular, this needs to be done before
freeing a unr, if a deletion of units could have been performed.
clean_unrhdrl()
Same as clean_unrhdr(), but assumes that the unr mutex is already
owned, if any.
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.
alloc_unr_specific(uh, item)
Allocate a specific unit number. This function allocates memory
and thus may sleep. The allocated unit number is returned on
success. If the specified number is already allocated or out of
the range, -1 is returned.
free_unr(uh, item)
Free a previously allocated unit number. This function may
require allocating memory, and thus it can sleep. There is no
pre-locked variant.
ITERATOR INTERFACE
The unr facility provides an interface to iterate over all allocated
units for the given unrhdr. Iterators are identified by an opaque
handle. More than one iterators can operate simultaneously; the iterator
position data is recorded only in the iterator handle.
Consumers must ensure that the unit allocator is not modified between
calls to the iterator functions. In particular, the internal allocator
mutex cannot provide consistency, because it is acquired and dropped
inside the next_iter_unr() function. If the allocator was modified, it
is safe to free the iterator with free_iter_unr() method nevertheless.
create_iter_unr(uh)
Create an iterator. Return the handle that should be passed to
other iterator functions.
next_iter_unr(handle)
Return the value of the next unit. Units are returned in
ascending order. A return value of -1 indicates the end of
iteration, in which case -1 is returned for all future calls.
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.
FreeBSD 14.0-RELEASE-p6 April 21, 2022 FreeBSD 14.0-RELEASE-p6