UNR(9)                 FreeBSD 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
             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.

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.

FreeBSD 13.1-RELEASE-p6         October 4, 2017        FreeBSD 13.1-RELEASE-p6