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

[hujianyang]

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 <hujiany...@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..b65e1ed 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 (&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

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