ovl: discard independent cursor in readdir()

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>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

1 files changed, 14 insertions, 24 deletions

diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 9df848f2e622..dcf1d412888d 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 list_head *cursor;
         struct file *realfile;
         struct file *upperfile;
 };
@@ -97,7 +96,6 @@ static struct ovl_cache_entry *ovl_cache_entry_new(struct dentry *dir,
         p->type = d_type;
         p->ino = ino;
         p->is_whiteout = false;
-        p->is_cursor = false;
 
         if (d_type == DT_CHR) {
                 struct dentry *dentry;
@@ -196,7 +194,6 @@ 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);
         WARN_ON(cache->refcount <= 0);
         cache->refcount--;
         if (!cache->refcount) {
@@ -254,6 +251,7 @@ static void ovl_dir_reset(struct file *file)
         if (cache && ovl_dentry_version_get(dentry) != cache->version) {
                 ovl_cache_put(od, dentry);
                 od->cache = NULL;
+                od->cursor = NULL;
         }
         WARN_ON(!od->is_real && !OVL_TYPE_MERGE(type));
         if (od->is_real && OVL_TYPE_MERGE(type))
@@ -295,17 +293,16 @@ static int ovl_dir_read_merged(struct dentry *dentry, struct list_head *list)
 
 static void ovl_seek_cursor(struct ovl_dir_file *od, loff_t pos)
 {
-        struct ovl_cache_entry *p;
+        struct list_head *p;
         loff_t off = 0;
 
-        list_for_each_entry(p, &od->cache->entries, l_node) {
-                if (p->is_cursor)
-                        continue;
+        list_for_each(p, &od->cache->entries) {
                 if (off >= pos)
                         break;
                 off++;
         }
-        list_move_tail(&od->cursor.l_node, &p->l_node);
+        /* Cursor is safe since the cache is stable */
+        od->cursor = p;
 }
 
 static struct ovl_dir_cache *ovl_cache_get(struct dentry *dentry)
@@ -344,6 +341,7 @@ static int ovl_iterate(struct file *file, struct dir_context *ctx)
 {
         struct ovl_dir_file *od = file->private_data;
         struct dentry *dentry = file->f_path.dentry;
+        struct ovl_cache_entry *p;
 
         if (!ctx->pos)
                 ovl_dir_reset(file);
@@ -362,19 +360,13 @@ 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;
-
-                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);
+        while (od->cursor != &od->cache->entries) {
+                p = list_entry(od->cursor, struct ovl_cache_entry, l_node);
+                if (!p->is_whiteout)
+                        if (!dir_emit(ctx, p->name, p->len, p->ino, p->type))
+                                break;
+                od->cursor = p->l_node.next;
+                ctx->pos++;
         }
         return 0;
 }
@@ -493,11 +485,9 @@ 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;
         file->private_data = od;
 
         return 0;