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 <chrism@mellanox.com> has promised to contribute
test-cases for idr_alloc_u32.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/idr.h b/include/linux/idr.h
index 7867d6117535..561a4cbabca6 100644
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -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);