exporting uuid_t from uapi/linux/uuid.h

Hello,

I'm doing some refactoring on btrfs and would like to convert some of
the "naked" definition of UUID in on-disk object to uuid_t. Since those
structs are defined in include/uapi/linux/btrfs_tree.h I naturally would
need to expose the kernel uuid_t to the uapi header via
include/uapi/linux/uuid.h. The uuid was originally unexported in
60927bc31436 ("uuid: remove uuid_be defintions from the uapi header")
 but at that time it was called uuid_be. The thing is that btrfs-progs
for example uses both btrfs_tree.h uapi header as well as libuuid. THe
latter also defines uuid_t. Both the kernel one and libuuid are binary
compatible.

So what's the correct way (if any) to expose a kernel type that might
have also been defined by a userspace library?

Regards,
Nikolay

On Tue, Aug 21, 2018 at 10:25:50PM +0300, Nikolay Borisov wrote:

Hello,

I'm doing some refactoring on btrfs and would like to convert some of
the "naked" definition of UUID in on-disk object to uuid_t. Since those
structs are defined in include/uapi/linux/btrfs_tree.h I naturally would
need to expose the kernel uuid_t to the uapi header via
include/uapi/linux/uuid.h. The uuid was originally unexported in
60927bc31436 ("uuid: remove uuid_be defintions from the uapi header")
 but at that time it was called uuid_be. The thing is that btrfs-progs
for example uses both btrfs_tree.h uapi header as well as libuuid. THe
latter also defines uuid_t. Both the kernel one and libuuid are binary
compatible.

So what's the correct way (if any) to expose a kernel type that might
have also been defined by a userspace library?

Please just use an raw array of __u8 for your APIs.