alloc_unr_specific(9) kernel unit number allocator

Other Alias

new_unrhdr, delete_unrhdr, alloc_unr, free_unr


In sys/systm.h Ft struct unrhdr * Fn new_unrhdr int low int high struct mtx *mutex Ft void Fn delete_unrhdr struct unrhdr *uh Ft int Fn alloc_unr struct unrhdr *uh Ft int Fn alloc_unrl struct unrhdr *uh Ft int Fn alloc_unr_specific struct unrhdr *uh u_int item Ft void Fn free_unr struct unrhdr *uh u_int item


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

Fn new_unrhdr low high mutex
Initialize a new unit number allocator entity. The Fa low and Fa 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 Fa mutex is not NULL it is used for locking when allocating and freeing units. Otherwise, internal mutex is used.
Fn delete_unrhdr uh
Destroy specified unit number allocator entity.
Fn 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.
Fn alloc_unrl uh
Same as Fn alloc_unr except that mutex is assumed to be already locked and thus is not used.
Fn 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.
Fn 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.


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


Kernel unit number allocator first appeared in Fx 6.0 .


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