Re: [PATCH RFC mdadm/master] mdadm: add support for new lockless bitmap

[Mariusz Tkaczyk <mtkaczyk@kernel.org>]

On Sun, 26 Jan 2025 16:27:14 +0800
Yu Kuai <yukuai1@huaweicloud.com> wrote:

> From: Yu Kuai <yukuai3@huawei.com>
> 
> A new major number 6 is used for the new bitmap.
> 
> Noted that for the kernel that doesn't support lockless bitmap, create
> such array will fail:
> 
> md0: invalid bitmap file superblock: unrecognized superblock version.
Hi Kuai,

Please go ahead and create branch on mdadm repo for lockness bitmap
implementation and keep your changes there. This is for sure not ready
and cannot be merged yet to main so sending it is not needed.

What do you think?
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>  Create.c | 5 ++++-
>  Grow.c   | 3 ++-
>  bitmap.h | 1 +
>  mdadm.c  | 9 ++++++++-
>  mdadm.h  | 1 +
>  super1.c | 9 +++++++++
>  6 files changed, 25 insertions(+), 3 deletions(-)
> 
> diff --git a/Create.c b/Create.c
> index fd6c9215..105d15e0 100644
> --- a/Create.c
> +++ b/Create.c
> @@ -541,6 +541,8 @@ int Create(struct supertype *st, struct
> mddev_ident *ident, int subdevs, pr_err("At least 2 nodes are needed
> for cluster-md\n"); return 1;
>  		}
> +	} else if (s->btype == BitmapLockless) {
> +		major_num = BITMAP_MAJOR_LOCKLESS;
>  	}
>  
>  	memset(&info, 0, sizeof(info));
> @@ -1182,7 +1184,8 @@ int Create(struct supertype *st, struct
> mddev_ident *ident, int subdevs,
>  	 * to stop another mdadm from finding and using those
> devices. */
>  
> -	if (s->btype == BitmapInternal || s->btype == BitmapCluster)
> {
> +	if (s->btype == BitmapInternal || s->btype == BitmapCluster
> ||
> +	    s->btype == BitmapLockless) {

This is asking to be moved to common helper function. Is is repeated 3
times at least so please consider (not sure about naming):

bool is_bitmap_supported(int btype) {
	if (btype == BitmapInternal || btype == BitmapCluster ||
	    btype == BitmapLockless)
		return true;
	return false;
}
Just a nit.