Re: [PATCH 3/4] xfs: expose the number of open zones in sysfs

[Damien Le Moal <dlemoal@kernel.org>]

On 3/30/26 14:40, Christoph Hellwig wrote:
> Add a sysfs attribute for the current number of open zones so that it
> can be trivially read from userspace in monitoring or testing software.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  Documentation/admin-guide/xfs.rst |  4 ++++
>  fs/xfs/xfs_sysfs.c                | 13 +++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/Documentation/admin-guide/xfs.rst b/Documentation/admin-guide/xfs.rst
> index 746ea60eed3f..eb3085421276 100644
> --- a/Documentation/admin-guide/xfs.rst
> +++ b/Documentation/admin-guide/xfs.rst
> @@ -550,6 +550,10 @@ For zoned file systems, the following attributes are exposed in:
>  	is limited by the capabilities of the backing zoned device, file system
>  	size and the max_open_zones mount option.
>  
> +  nr_open_zones			(Min:  1  Default:  Varies  Max:  UINTMAX)
> +	This read-only attribute exposes the current number of open zones
> +	used by the file system.
> +
>    zonegc_low_space		(Min:  0  Default:  0  Max:  100)
>  	Define a percentage for how much of the unused space that GC should keep
>  	available for writing. A high value will reclaim more of the space
> diff --git a/fs/xfs/xfs_sysfs.c b/fs/xfs/xfs_sysfs.c
> index 6c7909838234..43a02c622b6d 100644
> --- a/fs/xfs/xfs_sysfs.c
> +++ b/fs/xfs/xfs_sysfs.c
> @@ -13,6 +13,7 @@
>  #include "xfs_log.h"
>  #include "xfs_log_priv.h"
>  #include "xfs_mount.h"
> +#include "xfs_zone_priv.h"
>  #include "xfs_zones.h"
>  
>  struct xfs_sysfs_attr {
> @@ -718,6 +719,17 @@ max_open_zones_show(
>  }
>  XFS_SYSFS_ATTR_RO(max_open_zones);
>  
> +static ssize_t
> +nr_open_zones_show(
> +	struct kobject		*kobj,
> +	char			*buf)
> +{
> +	struct xfs_zone_info	*zi = zoned_to_mp(kobj)->m_zone_info;
> +
> +	return sysfs_emit(buf, "%u\n", zi->zi_nr_open_zones);

Since this is not an atomic, don't we need to copy this field into a local
variable under spin_lock(&zi->zi_open_zones_lock) ?


> +}
> +XFS_SYSFS_ATTR_RO(nr_open_zones);
> +
>  static ssize_t
>  zonegc_low_space_store(
>  	struct kobject		*kobj,
> @@ -751,6 +763,7 @@ XFS_SYSFS_ATTR_RW(zonegc_low_space);
>  
>  static struct attribute *xfs_zoned_attrs[] = {
>  	ATTR_LIST(max_open_zones),
> +	ATTR_LIST(nr_open_zones),
>  	ATTR_LIST(zonegc_low_space),
>  	NULL,
>  };


-- 
Damien Le Moal
Western Digital Research