DragonFly On-Line Manual Pages

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

NAME
     new_unrhdr, delete_unrhdr, alloc_unr, alloc_unr1, free_unr - kernel unit
     number allocator

SYNOPSIS
     #include <sys/systm.h>

     int
     alloc_unr(struct unrhdr *uh);

     int
     alloc_unrl(struct unrhdr *uh);

     void
     delete_unrhdr(struct unrhdr *uh);

     void
     free_unr(struct unrhdr *uh, u_int item);

     struct unrhdr *
     new_unrhdr(int low, int high, struct lock *lock);

DESCRIPTION
     The kernel unit number allocator is a generic facility, which allows to
     allocate unit numbers within a specified range.

     new_unrhdr(low, high, lock)
             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
             lock is not NULL, it is used for locking when allocating and
             freeing units.

     delete_unrhdr(uh)
             Delete specified unit number allocator entity.  This function
             frees the memory associated with the entity, it does not free any
             units.

     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 lock.  If no free unit numbers
             are left, -1 is returned.

     alloc_unrl(uh)
             Same as alloc_unr() except that lock 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.

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

SEE ALSO
     idr(9)

HISTORY
     Kernel unit number allocator first appeared in FreeBSD 6.0, and was
     imported into DragonFly 3.5.

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

DragonFly 6.5-DEVELOPMENT      January 20, 2026      DragonFly 6.5-DEVELOPMENT