Re: [PATCH 43/43] xfs: export max_open_zones in sysfs

["Darrick J. Wong" <djwong@kernel.org>]

On Thu, Feb 06, 2025 at 07:44:59AM +0100, Christoph Hellwig wrote:
> Add a zoned group with an attribute for the maximum number of open zones.
> This allows querying the open zones for data placement tests, or also
> for placement aware applications that are in control of the entire
> file system.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

It occurs to me -- what happens to all this zoned code if you build
without RT support?

Creating a whole sysfs kobj just to export a single attribute seems a
little overkill but I guess that beats revving the fs geometry ioctl.

Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  fs/xfs/xfs_mount.h |  1 +
>  fs/xfs/xfs_sysfs.c | 40 ++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 41 insertions(+)
> 
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index 7c7fd94375c1..390d9d5882f4 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -277,6 +277,7 @@ typedef struct xfs_mount {
>  #ifdef CONFIG_XFS_ONLINE_SCRUB_STATS
>  	struct xchk_stats	*m_scrub_stats;
>  #endif
> +	struct xfs_kobj		m_zoned_kobj;
>  	xfs_agnumber_t		m_agfrotor;	/* last ag where space found */
>  	atomic_t		m_agirotor;	/* last ag dir inode alloced */
>  	atomic_t		m_rtgrotor;	/* last rtgroup rtpicked */
> diff --git a/fs/xfs/xfs_sysfs.c b/fs/xfs/xfs_sysfs.c
> index c3bd7dff229d..797a92908647 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_zones.h"
>  
>  struct xfs_sysfs_attr {
>  	struct attribute attr;
> @@ -701,6 +702,34 @@ xfs_error_sysfs_init_class(
>  	return error;
>  }
>  
> +static inline struct xfs_mount *zoned_to_mp(struct kobject *kobj)
> +{
> +	return container_of(to_kobj(kobj), struct xfs_mount, m_zoned_kobj);
> +}
> +
> +static ssize_t
> +max_open_zones_show(
> +	struct kobject		*kobj,
> +	char			*buf)
> +{
> +	/* only report the open zones available for user data */
> +	return sysfs_emit(buf, "%u\n",
> +		zoned_to_mp(kobj)->m_max_open_zones - XFS_OPEN_GC_ZONES);
> +}
> +XFS_SYSFS_ATTR_RO(max_open_zones);
> +
> +static struct attribute *xfs_zoned_attrs[] = {
> +	ATTR_LIST(max_open_zones),
> +	NULL,
> +};
> +ATTRIBUTE_GROUPS(xfs_zoned);
> +
> +static const struct kobj_type xfs_zoned_ktype = {
> +	.release = xfs_sysfs_release,
> +	.sysfs_ops = &xfs_sysfs_ops,
> +	.default_groups = xfs_zoned_groups,
> +};
> +
>  int
>  xfs_mount_sysfs_init(
>  	struct xfs_mount	*mp)
> @@ -741,6 +770,14 @@ xfs_mount_sysfs_init(
>  	if (error)
>  		goto out_remove_error_dir;
>  
> +	if (xfs_has_zoned(mp)) {
> +		/* .../xfs/<dev>/zoned/ */
> +		error = xfs_sysfs_init(&mp->m_zoned_kobj, &xfs_zoned_ktype,
> +					&mp->m_kobj, "zoned");
> +		if (error)
> +			goto out_remove_error_dir;
> +	}
> +
>  	return 0;
>  
>  out_remove_error_dir:
> @@ -759,6 +796,9 @@ xfs_mount_sysfs_del(
>  	struct xfs_error_cfg	*cfg;
>  	int			i, j;
>  
> +	if (xfs_has_zoned(mp))
> +		xfs_sysfs_del(&mp->m_zoned_kobj);
> +
>  	for (i = 0; i < XFS_ERR_CLASS_MAX; i++) {
>  		for (j = 0; j < XFS_ERR_ERRNO_MAX; j++) {
>  			cfg = &mp->m_error_cfg[i][j];
> -- 
> 2.45.2
> 
>