[RFC PATCH v4 07/11] fs: statx add write zeroes unmap attribute

[Christoph Hellwig]

On Mon, Apr 21, 2025 at 10:15:05AM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang at huawei.com>
> 
> Add a new attribute flag to statx to determine whether a bdev or a file
> supports the unmap write zeroes command.
> 
> Signed-off-by: Zhang Yi <yi.zhang at huawei.com>
> ---
>  block/bdev.c              | 4 ++++
>  fs/ext4/inode.c           | 9 ++++++---
>  include/uapi/linux/stat.h | 1 +
>  3 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/block/bdev.c b/block/bdev.c
> index 4844d1e27b6f..29b0e5feb138 100644
> --- a/block/bdev.c
> +++ b/block/bdev.c
> @@ -1304,6 +1304,10 @@ void bdev_statx(struct path *path, struct kstat *stat,
>  			queue_atomic_write_unit_max_bytes(bd_queue));
>  	}
>  
> +	if (bdev_write_zeroes_unmap(bdev))
> +		stat->attributes |= STATX_ATTR_WRITE_ZEROES_UNMAP;
> +	stat->attributes_mask |= STATX_ATTR_WRITE_ZEROES_UNMAP;

Hmm, shouldn't this always be set by stat?  But I might just be
really confused what attributes_mask is, and might in fact have
misapplied it in past patches of my own..

Also shouldn't the patches to report the flag go into the bdev/ext4
patches that actually implement the feature for the respective files
to keep bisectability?