Re: [PATCH v5 17/17] vfs: expose delegation support to userland

On Wed 05-11-25 11:54:03, Jeff Layton wrote:
> Now that support for recallable directory delegations is available,
> expose this functionality to userland with new F_SETDELEG and F_GETDELEG
> commands for fcntl().
> 
> Note that this also allows userland to request a FL_DELEG type lease on
> files too. Userland applications that do will get signalled when there
> are metadata changes in addition to just data changes (which is a
> limitation of FL_LEASE leases).
> 
> These commands accept a new "struct delegation" argument that contains a
> flags field for future expansion.
> 
> Signed-off-by: Jeff Layton <[email protected]>

For new apis CCing linux-api is a good practice ;)

...

> diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
> index 3741ea1b73d8500061567b6590ccf5fb4c6770f0..8123fe70e03cfb1ba9ce1b5e20d61b62e462a7ea 100644
> --- a/include/uapi/linux/fcntl.h
> +++ b/include/uapi/linux/fcntl.h
> @@ -79,6 +79,16 @@
>   */
>  #define RWF_WRITE_LIFE_NOT_SET	RWH_WRITE_LIFE_NOT_SET
>  
> +/* Set/Get delegations */
> +#define F_GETDELEG		(F_LINUX_SPECIFIC_BASE + 15)
> +#define F_SETDELEG		(F_LINUX_SPECIFIC_BASE + 16)
> +
> +/* Argument structure for F_GETDELEG and F_SETDELEG */
> +struct delegation {
> +	unsigned int	d_flags;	/* Must be 0 */
> +	short		d_type;		/* F_RDLCK, F_WRLCK, F_UNLCK */
> +};
> +

I think it would make sense for d_type to be unsigned since it's more or
less enum. Also struct delegation is going to have a hole in it at the end
which is always a concern with uAPI structures (passing around
uninitialized stuff). I think it would be good to put an explicit padding
there and enforce it is zeroed out.

								Honza

-- 
Jan Kara <[email protected]>
SUSE Labs, CR