[PATCH RFC] ovl: discard independent cursor in readdir()

[hujianyang <hujianyang@huawei.com>]

Since the ovl_dir_cache is stable during a directory reading, the cursor
of struct ovl_dir_file don't need to be an independent entry in the list
of a merged directory.

This patch changes *cursor* to a pointer which points to the entry in the
ovl_dir_cache. After this, we don't need to check *is_cursor* either.

Signed-off-by: hujianyang <hujianyang@huawei.com>
---
 fs/overlayfs/readdir.c |   33 ++++++++++++---------------------
 1 files changed, 12 insertions(+), 21 deletions(-)

diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 8087b63..0e46aab 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -24,7 +24,6 @@ struct ovl_cache_entry {
 	struct list_head l_node;
 	struct rb_node node;
 	bool is_whiteout;
-	bool is_cursor;
 	char name[];
 };

@@ -49,7 +48,7 @@ struct ovl_dir_file {
 	bool is_real;
 	bool is_upper;
 	struct ovl_dir_cache *cache;
-	struct ovl_cache_entry cursor;
+	struct ovl_cache_entry *cursor;
 	struct file *realfile;
 	struct file *upperfile;
 };
@@ -94,7 +93,6 @@ static struct ovl_cache_entry *ovl_cache_entry_new(const char *name, int len,
 		p->type = d_type;
 		p->ino = ino;
 		p->is_whiteout = false;
-		p->is_cursor = false;
 	}

 	return p;
@@ -195,7 +193,7 @@ static void ovl_cache_put(struct ovl_dir_file *od, struct dentry *dentry)
 {
 	struct ovl_dir_cache *cache = od->cache;

-	list_del_init(&od->cursor.l_node);
+	od->cursor = NULL;
 	WARN_ON(cache->refcount <= 0);
 	cache->refcount--;
 	if (!cache->refcount) {
@@ -298,13 +296,12 @@ static void ovl_seek_cursor(struct ovl_dir_file *od, loff_t pos)
 	loff_t off = 0;

 	list_for_each_entry(p, &od->cache->entries, l_node) {
-		if (p->is_cursor)
-			continue;
 		if (off >= pos)
 			break;
 		off++;
 	}
-	list_move_tail(&od->cursor.l_node, &p->l_node);
+	/* Curosr is safe since the cache is stable */
+	od->cursor = p;
 }

 static struct ovl_dir_cache *ovl_cache_get(struct dentry *dentry)
@@ -361,19 +358,14 @@ static int ovl_iterate(struct file *file, struct dir_context *ctx)
 		ovl_seek_cursor(od, ctx->pos);
 	}

-	while (od->cursor.l_node.next != &od->cache->entries) {
-		struct ovl_cache_entry *p;
+	while (!list_is_last(&od->cursor->l_node, &od->cache->entries)) {
+		struct ovl_cache_entry *p = od->cursor;

-		p = list_entry(od->cursor.l_node.next, struct ovl_cache_entry, l_node);
-		/* Skip cursors */
-		if (!p->is_cursor) {
-			if (!p->is_whiteout) {
-				if (!dir_emit(ctx, p->name, p->len, p->ino, p->type))
-					break;
-			}
-			ctx->pos++;
-		}
-		list_move(&od->cursor.l_node, &p->l_node);
+		if (!p->is_whiteout)
+			if (!dir_emit(ctx, p->name, p->len, p->ino, p->type))
+				break;
+		od->cursor = list_next_entry(p, l_node);
+		ctx->pos++;
 	}
 	return 0;
 }
@@ -492,11 +484,10 @@ static int ovl_dir_open(struct inode *inode, struct file *file)
 		kfree(od);
 		return PTR_ERR(realfile);
 	}
-	INIT_LIST_HEAD(&od->cursor.l_node);
 	od->realfile = realfile;
 	od->is_real = !OVL_TYPE_MERGE(type);
 	od->is_upper = OVL_TYPE_UPPER(type);
-	od->cursor.is_cursor = true;
+	od->cursor = NULL;
 	file->private_data = od;

 	return 0;
-- 
1.6.0.2