Provided by: freebsd-manpages_8.2-1_all bug

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 allocating 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, item)
             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 FreeBSD 6.0.


AUTHORS
     Kernel unit number allocator was written by Poul-Henning Kamp.  This
     manpage was written by Gleb Smirnoff.