ext4: add a new ioctl EXT4_IOC_CLEAR_ES_CACHE

The new ioctl EXT4_IOC_CLEAR_ES_CACHE will force an inode's extent
status cache to be cleared out.  This is intended for use for
debugging.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -649,6 +649,8 @@ enum {
 #define EXT4_IOC_SET_ENCRYPTION_POLICY	FS_IOC_SET_ENCRYPTION_POLICY
 #define EXT4_IOC_GET_ENCRYPTION_PWSALT	FS_IOC_GET_ENCRYPTION_PWSALT
 #define EXT4_IOC_GET_ENCRYPTION_POLICY	FS_IOC_GET_ENCRYPTION_POLICY
+/* ioctl codes 19--39 are reserved for fscrypt */
+#define EXT4_IOC_CLEAR_ES_CACHE		_IO('f', 40)
 
 #define EXT4_IOC_FSGETXATTR		FS_IOC_FSGETXATTR
 #define EXT4_IOC_FSSETXATTR		FS_IOC_FSSETXATTR

fs/ext4/extents_status.c

@@ -1374,6 +1374,34 @@ static int es_reclaim_extents(struct ext4_inode_info *ei, int *nr_to_scan)
 	return nr_shrunk;
 }
 
+/*
+ * Called to support EXT4_IOC_CLEAR_ES_CACHE.  We can only remove
+ * discretionary entries from the extent status cache.  (Some entries
+ * must be present for proper operations.)
+ */
+void ext4_clear_inode_es(struct inode *inode)
+{
+	struct ext4_inode_info *ei = EXT4_I(inode);
+	struct extent_status *es;
+	struct ext4_es_tree *tree;
+	struct rb_node *node;
+
+	write_lock(&ei->i_es_lock);
+	tree = &EXT4_I(inode)->i_es_tree;
+	tree->cache_es = NULL;
+	node = rb_first(&tree->root);
+	while (node) {
+		es = rb_entry(node, struct extent_status, rb_node);
+		node = rb_next(node);
+		if (!ext4_es_is_delayed(es)) {
+			rb_erase(&es->rb_node, &tree->root);
+			ext4_es_free_extent(inode, es);
+		}
+	}
+	ext4_clear_inode_state(inode, EXT4_STATE_EXT_PRECACHED);
+	write_unlock(&ei->i_es_lock);
+}
+
 #ifdef ES_DEBUG__
 static void ext4_print_pending_tree(struct inode *inode)
 {

fs/ext4/extents_status.h

@@ -248,5 +248,6 @@ extern unsigned int ext4_es_delayed_clu(struct inode *inode, ext4_lblk_t lblk,
 					ext4_lblk_t len);
 extern void ext4_es_remove_blks(struct inode *inode, ext4_lblk_t lblk,
 				ext4_lblk_t len);
+extern void ext4_clear_inode_es(struct inode *inode);
 
 #endif /* _EXT4_EXTENTS_STATUS_H */

fs/ext4/ioctl.c

@@ -1115,6 +1115,14 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	case EXT4_IOC_GET_ENCRYPTION_POLICY:
 		return fscrypt_ioctl_get_policy(filp, (void __user *)arg);
 
+	case EXT4_IOC_CLEAR_ES_CACHE:
+	{
+		if (!inode_owner_or_capable(inode))
+			return -EACCES;
+		ext4_clear_inode_es(inode);
+		return 0;
+	}
+
 	case EXT4_IOC_FSGETXATTR:
 	{
 		struct fsxattr fa;
@@ -1233,6 +1241,7 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case EXT4_IOC_GET_ENCRYPTION_POLICY:
 	case EXT4_IOC_SHUTDOWN:
 	case FS_IOC_GETFSMAP:
+	case EXT4_IOC_CLEAR_ES_CACHE:
 		break;
 	default:
 		return -ENOIOCTLCMD;