Add support for parsing the subvolume_id field from InodeStat v9 and
storing it in the inode for later use by subvolume metrics tracking.

The subvolume_id identifies which CephFS subvolume an inode belongs to,
enabling per-subvolume I/O metrics collection and reporting.

This patch:
- Adds subvolume_id field to struct ceph_mds_reply_info_in
- Adds i_subvolume_id field to struct ceph_inode_info
- Parses subvolume_id from v9 InodeStat in parse_reply_info_in()
- Adds ceph_inode_set_subvolume() helper to propagate the ID to inodes
- Initializes i_subvolume_id in inode allocation and clears on destroy

Signed-off-by: Alex Markuze <amarkuze@redhat.com>
---
 fs/ceph/inode.c      | 23 +++++++++++++++++++++++
 fs/ceph/mds_client.c |  7 +++++++
 fs/ceph/mds_client.h |  1 +
 fs/ceph/super.h      |  2 ++
 4 files changed, 33 insertions(+)

diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index a6e260d9e420..835049004047 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -638,6 +638,7 @@ struct inode *ceph_alloc_inode(struct super_block *sb)
 
 	ci->i_max_bytes = 0;
 	ci->i_max_files = 0;
+	ci->i_subvolume_id = 0;
 
 	memset(&ci->i_dir_layout, 0, sizeof(ci->i_dir_layout));
 	memset(&ci->i_cached_layout, 0, sizeof(ci->i_cached_layout));
@@ -742,6 +743,8 @@ void ceph_evict_inode(struct inode *inode)
 
 	percpu_counter_dec(&mdsc->metric.total_inodes);
 
+	ci->i_subvolume_id = 0;
+
 	netfs_wait_for_outstanding_io(inode);
 	truncate_inode_pages_final(&inode->i_data);
 	if (inode->i_state & I_PINNING_NETFS_WB)
@@ -873,6 +876,22 @@ int ceph_fill_file_size(struct inode *inode, int issued,
 	return queue_trunc;
 }
 
+/*
+ * Set the subvolume ID for an inode. Following the FUSE client convention,
+ * 0 means unknown/unset (MDS only sends non-zero IDs for subvolume inodes).
+ */
+void ceph_inode_set_subvolume(struct inode *inode, u64 subvolume_id)
+{
+	struct ceph_inode_info *ci;
+
+	if (!inode || !subvolume_id)
+		return;
+
+	ci = ceph_inode(inode);
+	if (READ_ONCE(ci->i_subvolume_id) != subvolume_id)
+		WRITE_ONCE(ci->i_subvolume_id, subvolume_id);
+}
+
 void ceph_fill_file_time(struct inode *inode, int issued,
 			 u64 time_warp_seq, struct timespec64 *ctime,
 			 struct timespec64 *mtime, struct timespec64 *atime)
@@ -1087,6 +1106,7 @@ int ceph_fill_inode(struct inode *inode, struct page *locked_page,
 	new_issued = ~issued & info_caps;
 
 	__ceph_update_quota(ci, iinfo->max_bytes, iinfo->max_files);
+	ceph_inode_set_subvolume(inode, iinfo->subvolume_id);
 
 #ifdef CONFIG_FS_ENCRYPTION
 	if (iinfo->fscrypt_auth_len &&
@@ -1594,6 +1614,8 @@ int ceph_fill_trace(struct super_block *sb, struct ceph_mds_request *req)
 			goto done;
 		}
 		if (parent_dir) {
+			ceph_inode_set_subvolume(parent_dir,
+						 rinfo->diri.subvolume_id);
 			err = ceph_fill_inode(parent_dir, NULL, &rinfo->diri,
 					      rinfo->dirfrag, session, -1,
 					      &req->r_caps_reservation);
@@ -1682,6 +1704,7 @@ int ceph_fill_trace(struct super_block *sb, struct ceph_mds_request *req)
 		BUG_ON(!req->r_target_inode);
 
 		in = req->r_target_inode;
+		ceph_inode_set_subvolume(in, rinfo->targeti.subvolume_id);
 		err = ceph_fill_inode(in, req->r_locked_page, &rinfo->targeti,
 				NULL, session,
 				(!test_bit(CEPH_MDS_R_ABORTED, &req->r_req_flags) &&
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index d7d8178e1f9a..099b8f22683b 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -105,6 +105,8 @@ static int parse_reply_info_in(void **p, void *end,
 	int err = 0;
 	u8 struct_v = 0;
 
+	info->subvolume_id = 0;
+
 	if (features == (u64)-1) {
 		u32 struct_len;
 		u8 struct_compat;
@@ -251,6 +253,10 @@ static int parse_reply_info_in(void **p, void *end,
 			ceph_decode_skip_n(p, end, v8_struct_len, bad);
 		}
 
+		/* struct_v 9 added subvolume_id */
+		if (struct_v >= 9)
+			ceph_decode_64_safe(p, end, info->subvolume_id, bad);
+
 		*p = end;
 	} else {
 		/* legacy (unversioned) struct */
@@ -3970,6 +3976,7 @@ static void handle_reply(struct ceph_mds_session *session, struct ceph_msg *msg)
 			goto out_err;
 		}
 		req->r_target_inode = in;
+		ceph_inode_set_subvolume(in, rinfo->targeti.subvolume_id);
 	}
 
 	mutex_lock(&session->s_mutex);
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index 0428a5eaf28c..bd3690baa65c 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -118,6 +118,7 @@ struct ceph_mds_reply_info_in {
 	u32 fscrypt_file_len;
 	u64 rsnaps;
 	u64 change_attr;
+	u64 subvolume_id;
 };
 
 struct ceph_mds_reply_dir_entry {
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index a1f781c46b41..c0372a725960 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -385,6 +385,7 @@ struct ceph_inode_info {
 
 	/* quotas */
 	u64 i_max_bytes, i_max_files;
+	u64 i_subvolume_id;	/* 0 = unknown/unset, matches FUSE client */
 
 	s32 i_dir_pin;
 
@@ -1057,6 +1058,7 @@ extern struct inode *ceph_get_inode(struct super_block *sb,
 extern struct inode *ceph_get_snapdir(struct inode *parent);
 extern int ceph_fill_file_size(struct inode *inode, int issued,
 			       u32 truncate_seq, u64 truncate_size, u64 size);
+extern void ceph_inode_set_subvolume(struct inode *inode, u64 subvolume_id);
 extern void ceph_fill_file_time(struct inode *inode, int issued,
 				u64 time_warp_seq, struct timespec64 *ctime,
 				struct timespec64 *mtime,
-- 
2.34.1