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UNR(9)			 BSD Kernel Developer's	Manual			UNR(9)

NAME
     new_unrhdr, clear_unrhdr, delete_unrhdr, alloc_unr, alloc_unr_specific,
     free_unr -- kernel	unit number allocator

SYNOPSIS
     #include <sys/systm.h>

     struct unrhdr *
     new_unrhdr(int low, int high, struct mtx *mutex);

     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);

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.  Otherwise,	internal mutex is used.

     clear_unrhdr(uh)
	     Clear all units from the specified	unit number allocator entity.
	     This function resets the entity as	if it were just	initialized
	     with new_unrhdr().

     delete_unrhdr(uh)
	     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().

     alloc_unr(uh)
	     Return a new unit number.	The lowest free	number is always allo-
	     cated.  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 re-
	     quire 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 man-
     page was written by Gleb Smirnoff.

BSD				October	4, 2017				   BSD

NAME | SYNOPSIS | DESCRIPTION | CODE REFERENCES | HISTORY | AUTHORS

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