From 5cee788f85c03e72a78f0fa3347d499e4db1d621 Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@lst.de>
Date: Tue, 21 Jan 2025 06:45:22 +0100
Subject: [PATCH] xfs: export max_open_zones in sysfs

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>
---
 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 @@ out_error:
 	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];
-- 
2.50.1