Re: [PATCH 1/5] btrfs: add flags to give an hint to the chunk allocator

[Josef Bacik <josef@toxicpanda.com>]

On Sun, Mar 06, 2022 at 07:14:39PM +0100, Goffredo Baroncelli wrote:
> From: Goffredo Baroncelli <kreijack@inwind.it>
> 
> Add the following flags to give an hint about which chunk should be
> allocated in which disk:
> 
> - BTRFS_DEV_ALLOCATION_HINT_DATA_PREFERRED
>   preferred for data chunk, but metadata chunk allowed
> - BTRFS_DEV_ALLOCATION_HINT_METADATA_PREFERRED
>   preferred for metadata chunk, but data chunk allowed
> - BTRFS_DEV_ALLOCATION_HINT_METADATA_ONLY
>   only metadata chunk allowed
> - BTRFS_DEV_ALLOCATION_HINT_DATA_ONLY
>   only data chunk allowed
> 
> Signed-off-by: Goffredo Baroncelli <kreijack@inwind.it>
> ---
>  include/uapi/linux/btrfs_tree.h | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/include/uapi/linux/btrfs_tree.h b/include/uapi/linux/btrfs_tree.h
> index b069752a8ecf..e0d842c2e616 100644
> --- a/include/uapi/linux/btrfs_tree.h
> +++ b/include/uapi/linux/btrfs_tree.h
> @@ -389,6 +389,22 @@ struct btrfs_key {
>  	__u64 offset;
>  } __attribute__ ((__packed__));
>  
> +/* dev_item.type */
> +
> +/* btrfs chunk allocation hint */
> +#define BTRFS_DEV_ALLOCATION_HINT_BIT_COUNT	2
> +/* btrfs chunk allocation hint mask */
> +#define BTRFS_DEV_ALLOCATION_HINT_MASK	\
> +	((1 << BTRFS_DEV_ALLOCATION_HINT_BIT_COUNT) - 1)
> +/* preferred data chunk, but metadata chunk allowed */
> +#define BTRFS_DEV_ALLOCATION_HINT_DATA_PREFERRED	(0ULL)

Actually don't we have 0 set on type already?  So this will make all existing
file systems have DATA_PREFERRED, when in reality they may not want that
behavior.  So should we start at 1?  Thanks,

Josef