From 3d93570979967b685145c7126098a419eda9fc29 Mon Sep 17 00:00:00 2001
From: chrislu <chris.lu@gmail.com>
Date: Sun, 13 Feb 2022 03:31:47 -0800
Subject: [PATCH] supports forget

---
 weed/mount/inode_to_path.go | 12 +++++++++
 weed/mount/weedfs.go        |  1 +
 weed/mount/weedfs_forget.go | 52 +++++++++++++++++++++++++++++++++++++
 3 files changed, 65 insertions(+)
 create mode 100644 weed/mount/weedfs_forget.go

diff --git a/weed/mount/inode_to_path.go b/weed/mount/inode_to_path.go
index 21e6c867c..6650f2380 100644
--- a/weed/mount/inode_to_path.go
+++ b/weed/mount/inode_to_path.go
@@ -82,3 +82,15 @@ func (i *InodeToPath) RemovePath(path util.FullPath) {
 		delete(i.inode2path, inode)
 	}
 }
+func (i *InodeToPath) RemoveInode(inode uint64) {
+	if inode == 1 {
+		return
+	}
+	i.RLock()
+	defer i.RUnlock()
+	path, found := i.inode2path[inode]
+	if found {
+		delete(i.path2inode, path)
+		delete(i.inode2path, inode)
+	}
+}
diff --git a/weed/mount/weedfs.go b/weed/mount/weedfs.go
index 6788b0b36..a36e4dc97 100644
--- a/weed/mount/weedfs.go
+++ b/weed/mount/weedfs.go
@@ -120,6 +120,7 @@ func (wfs *WFS) maybeLoadEntry(fullpath util.FullPath) (*filer_pb.Entry, fuse.St
 		}, fuse.OK
 	}
 
+	// TODO Use inode to selectively filetering metadata updates
 	// read from async meta cache
 	meta_cache.EnsureVisited(wfs.metaCache, wfs, util.FullPath(dir))
 	cachedEntry, cacheErr := wfs.metaCache.FindEntry(context.Background(), fullpath)
diff --git a/weed/mount/weedfs_forget.go b/weed/mount/weedfs_forget.go
new file mode 100644
index 000000000..2d09a473b
--- /dev/null
+++ b/weed/mount/weedfs_forget.go
@@ -0,0 +1,52 @@
+package mount
+
+// Forget is called when the kernel discards entries from its
+// dentry cache. This happens on unmount, and when the kernel
+// is short on memory. Since it is not guaranteed to occur at
+// any moment, and since there is no return value, Forget
+// should not do I/O, as there is no channel to report back
+// I/O errors.
+// from https://github.com/libfuse/libfuse/blob/master/include/fuse_lowlevel.h
+/**
+ * Forget about an inode
+ *
+ * This function is called when the kernel removes an inode
+ * from its internal caches.
+ *
+ * The inode's lookup count increases by one for every call to
+ * fuse_reply_entry and fuse_reply_create. The nlookup parameter
+ * indicates by how much the lookup count should be decreased.
+ *
+ * Inodes with a non-zero lookup count may receive request from
+ * the kernel even after calls to unlink, rmdir or (when
+ * overwriting an existing file) rename. Filesystems must handle
+ * such requests properly and it is recommended to defer removal
+ * of the inode until the lookup count reaches zero. Calls to
+ * unlink, rmdir or rename will be followed closely by forget
+ * unless the file or directory is open, in which case the
+ * kernel issues forget only after the release or releasedir
+ * calls.
+ *
+ * Note that if a file system will be exported over NFS the
+ * inodes lifetime must extend even beyond forget. See the
+ * generation field in struct fuse_entry_param above.
+ *
+ * On unmount the lookup count for all inodes implicitly drops
+ * to zero. It is not guaranteed that the file system will
+ * receive corresponding forget messages for the affected
+ * inodes.
+ *
+ * Valid replies:
+ *   fuse_reply_none
+ *
+ * @param req request handle
+ * @param ino the inode number
+ * @param nlookup the number of lookups to forget
+ */
+func (wfs *WFS) Forget(nodeid, nlookup uint64) {
+	if nlookup == 0 {
+		// need to maintain the inode for selective filtering
+		// and caching for metadata updates
+		wfs.inodeToPath.RemoveInode(nodeid)
+	}
+}