[PATCH 10/21] NFSv4/flexfiles: Implement in-place device re-resolve on CHANGE

Implement the reresolve_deviceid hook: walk the layout's mirrors and,
for every stripe whose raw deviceid matches the changed one, exchange
the pinned device node out for NULL.  In-flight I/O completes on the old
node through its own reference; the next I/O to the stripe re-resolves
via ff_layout_get_mirror_ds() and picks up the server's new mapping
with a fresh GETDEVICEINFO.  The un-pinned references are handed back
on the walker's list to be put outside the locks.

Matching uses the raw deviceid decoded from the layout (dss[].devid), so
stripes whose node was never resolved, or already exchanged, are
untouched.  Nothing dispatches CHANGE to the walker yet: no behavior
change.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Benjamin Coddington <bcodding-F/[email protected]>
---
 fs/nfs/flexfilelayout/flexfilelayout.c | 36 ++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/fs/nfs/flexfilelayout/flexfilelayout.c b/fs/nfs/flexfilelayout/flexfilelayout.c
index dfc0c298ab4b..bb27bbea6c95 100644
--- a/fs/nfs/flexfilelayout/flexfilelayout.c
+++ b/fs/nfs/flexfilelayout/flexfilelayout.c
@@ -2505,6 +2505,41 @@ static void ff_layout_cancel_io(struct pnfs_layout_segment *lseg)
 	}
 }
 
+/*
+ * The server changed the mapping for deviceid @id (CB_NOTIFY_DEVICEID
+ * CHANGE).  Un-pin every stripe device node resolved from @id in @lo's
+ * mirrors: in-flight I/O completes on the old node via its own
+ * reference, and the next I/O to the stripe re-resolves, picking up the
+ * new mapping with a fresh GETDEVICEINFO (the stale cache entry has
+ * already been unhashed).
+ *
+ * Called under @lo's inode i_lock; the un-pinned references are handed
+ * to the caller on @head to put outside the lock.
+ */
+static void ff_layout_reresolve_deviceid(struct pnfs_layout_hdr *lo,
+					 const struct nfs4_deviceid *id,
+					 bool immediate,
+					 struct list_head *head)
+{
+	struct nfs4_flexfile_layout *flo = FF_LAYOUT_FROM_HDR(lo);
+	struct nfs4_ff_layout_mirror *mirror;
+	struct nfs4_ff_layout_ds *old;
+	u32 dss_id;
+
+	list_for_each_entry(mirror, &flo->mirrors, mirrors) {
+		for (dss_id = 0; dss_id < mirror->dss_count; dss_id++) {
+			if (memcmp(&mirror->dss[dss_id].devid, id,
+				   sizeof(*id)) != 0)
+				continue;
+			old = unrcu_pointer(
+				xchg(&mirror->dss[dss_id].mirror_ds, NULL));
+			if (IS_ERR_OR_NULL(old))
+				continue;
+			list_add(&old->id_node.put_list, head);
+		}
+	}
+}
+
 static struct pnfs_ds_commit_info *
 ff_layout_get_ds_info(struct inode *inode)
 {
@@ -3088,6 +3123,7 @@ static struct pnfs_layoutdriver_type flexfilelayout_type = {
 	.pg_write_ops		= &ff_layout_pg_write_ops,
 	.get_ds_info		= ff_layout_get_ds_info,
 	.free_deviceid_node	= ff_layout_free_deviceid_node,
+	.reresolve_deviceid	= ff_layout_reresolve_deviceid,
 	.read_pagelist		= ff_layout_read_pagelist,
 	.write_pagelist		= ff_layout_write_pagelist,
 	.alloc_deviceid_node    = ff_layout_alloc_deviceid_node,
-- 
2.53.0