Commit e096f6a7 authored by Matthew Wilcox's avatar Matthew Wilcox

idr: Add idr_alloc_u32 helper

All current users of idr_alloc_ext() actually want to allocate a u32
and idr_alloc_u32() fits their needs better.

Like idr_get_next(), it uses a 'nextid' argument which serves as both
a pointer to the start ID and the assigned ID (instead of a separate
minimum and pointer-to-assigned-ID argument).  It uses a 'max' argument
rather than 'end' because the semantics that idr_alloc has for 'end'
don't work well for unsigned types.

Since idr_alloc_u32() returns an errno instead of the allocated ID, mark
it as __must_check to help callers use it correctly.  Include copious
kernel-doc.  Chris Mi <> has promised to contribute
test-cases for idr_alloc_u32.
Signed-off-by: default avatarMatthew Wilcox <>
parent 322d884b
......@@ -131,6 +131,8 @@ static inline int idr_alloc_ext(struct idr *idr, void *ptr,
return idr_alloc_cmn(idr, ptr, index, start, end, gfp, true);
int __must_check idr_alloc_u32(struct idr *, void *ptr, u32 *nextid,
unsigned long max, gfp_t);
int idr_alloc_cyclic(struct idr *, void *entry, int start, int end, gfp_t);
int idr_for_each(const struct idr *,
int (*fn)(int id, void *p, void *data), void *data);
......@@ -7,6 +7,37 @@
DEFINE_PER_CPU(struct ida_bitmap *, ida_bitmap);
static DEFINE_SPINLOCK(simple_ida_lock);
* idr_alloc_u32() - Allocate an ID.
* @idr: IDR handle.
* @ptr: Pointer to be associated with the new ID.
* @nextid: Pointer to an ID.
* @max: The maximum ID to allocate (inclusive).
* @gfp: Memory allocation flags.
* Allocates an unused ID in the range specified by @nextid and @max.
* Note that @max is inclusive whereas the @end parameter to idr_alloc()
* is exclusive.
* The caller should provide their own locking to ensure that two
* concurrent modifications to the IDR are not possible. Read-only
* accesses to the IDR may be done under the RCU read lock or may
* exclude simultaneous writers.
* Return: 0 if an ID was allocated, -ENOMEM if memory allocation failed,
* or -ENOSPC if no free IDs could be found. If an error occurred,
* @nextid is unchanged.
int idr_alloc_u32(struct idr *idr, void *ptr, u32 *nextid,
unsigned long max, gfp_t gfp)
unsigned long tmp = *nextid;
int ret = idr_alloc_ext(idr, ptr, &tmp, tmp, max + 1, gfp);
*nextid = tmp;
return ret;
int idr_alloc_cmn(struct idr *idr, void *ptr, unsigned long *index,
unsigned long start, unsigned long end, gfp_t gfp,
bool ext)
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