Add scoutfs_item_forget()

Add a forget call which forcefully removes an item, no matter it's
state.   The page cache will use this in invalidate page to drop
ephemeral items that reference a dirty page that's being truncated.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/counters.h

@@ -28,6 +28,7 @@
 	EXPAND_COUNTER(item_lookup_hit)		\
 	EXPAND_COUNTER(item_lookup_miss)	\
 	EXPAND_COUNTER(item_delete)		\
+	EXPAND_COUNTER(item_forget)		\
 	EXPAND_COUNTER(item_range_hit)		\
 	EXPAND_COUNTER(item_range_miss)		\
 	EXPAND_COUNTER(item_range_insert)

kmod/src/item.c

@@ -1105,6 +1105,32 @@ out:
 	return ret;
 }
 
+/*
+ * Forcefully remove an item from the cache regardless of its state or
+ * relationship to persistent items.
+ *
+ * The caller is entirely responsible for the correctness of having this
+ * item vanish.
+ */
+void scoutfs_item_forget(struct super_block *sb, struct scoutfs_key_buf *key)
+{
+	struct scoutfs_sb_info *sbi = SCOUTFS_SB(sb);
+	struct item_cache *cac = sbi->item_cache;
+	struct cached_item *item;
+	unsigned long flags;
+
+	spin_lock_irqsave(&cac->lock, flags);
+
+	item = find_item(sb, &cac->items, key);
+	if (item) {
+		trace_printk("forgetting item %p\n", item);
+		scoutfs_inc_counter(sb, item_forget);
+		erase_item(sb, cac, item);
+	}
+
+	spin_unlock_irqrestore(&cac->lock, flags);
+}
+
 /*
  * Return the first dirty node in the subtree starting at the given node.
  */

kmod/src/item.h

@@ -31,6 +31,7 @@ void scoutfs_item_delete_dirty(struct super_block *sb,
 int scoutfs_item_delete_many(struct super_block *sb,
 			     struct scoutfs_key_buf **keys, unsigned nr);
 int scoutfs_item_delete(struct super_block *sb, struct scoutfs_key_buf *key);
+void scoutfs_item_forget(struct super_block *sb, struct scoutfs_key_buf *key);
 
 int scoutfs_item_add_batch(struct super_block *sb, struct list_head *list,
 			   struct scoutfs_key_buf *key, struct kvec *val);