centos man page for idr_alloc

IDR_ALLOC(9)						  Basic Kernel Library Functions					      IDR_ALLOC(9)

NAME
       idr_alloc - allocate new idr entry

SYNOPSIS
       int idr_alloc(struct idr * idr, void * ptr, int start, int end, gfp_t gfp_mask);

ARGUMENTS
       idr
	   the (initialized) idr

       ptr
	   pointer to be associated with the new id

       start
	   the minimum id (inclusive)

       end
	   the maximum id (exclusive, <= 0 for max)

       gfp_mask
	   memory allocation flags

DESCRIPTION
       Allocate an id in [start, end) and associate it with ptr. If no ID is available in the specified range, returns -ENOSPC. On memory
       allocation failure, returns -ENOMEM.

       Note that end is treated as max when <= 0. This is to always allow using start + N as end as long as N is inside integer range.

       The user is responsible for exclusively synchronizing all operations which may modify idr. However, read-only accesses such as idr_find or
       iteration can be performed under RCU read lock provided the user destroys ptr in RCU-safe way after removal from idr.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014							      IDR_ALLOC(9)