fix(mount): add -posixDirNlink option for correct directory nlink

Add optional POSIX-compliant directory nlink counting
(nlink = 2 + number_of_subdirectories) behind the -posixDirNlink
flag. This requires listing cached directory entries on every stat,
which has a performance cost, so it's off by default.

When disabled (default), directories report nlink=2, which is the
POSIX-compliant baseline for empty directories and a common default
in distributed filesystems.

- Set nlink baseline to 2 for all directories (was 1)
- Add applyDirNlink() gated behind option.PosixDirNlink
- Add -posixDirNlink CLI flag

weed/command/mount.go

@@ -56,6 +56,7 @@ type MountOptions struct {
 	distributedLock *bool
 
 	// FUSE performance options
+	posixDirNlink  *bool
 	writebackCache *bool
 	asyncDio       *bool
 	cacheSymlink   *bool
@@ -132,6 +133,7 @@ func init() {
 	mountOptions.distributedLock = cmdMount.Flag.Bool("dlm", false, "enable distributed lock for cross-mount write coordination (only one mount can write a file at a time)")
 
 	// FUSE performance options
+	mountOptions.posixDirNlink = cmdMount.Flag.Bool("posix.dirNLink", false, "report POSIX-compliant directory nlink (2 + subdirectory count); costs one directory listing per stat")
 	mountOptions.writebackCache = cmdMount.Flag.Bool("writebackCache", false, "enable FUSE writeback cache for improved write performance (at risk of data loss on crash)")
 	mountOptions.asyncDio = cmdMount.Flag.Bool("asyncDio", false, "enable async direct I/O for better concurrency")
 	mountOptions.cacheSymlink = cmdMount.Flag.Bool("cacheSymlink", false, "enable symlink caching to reduce metadata lookups")

weed/command/mount_std.go

@@ -354,6 +354,7 @@ func RunMount(option *MountOptions, umask os.FileMode) bool {
 		DirIdleEvictSec:   *option.dirIdleEvictSec,
 		EnableDistributedLock: option.distributedLock != nil && *option.distributedLock,
 		WritebackCache:       option.writebackCache != nil && *option.writebackCache,
+		PosixDirNlink:        option.posixDirNlink != nil && *option.posixDirNlink,
 	})
 
 	// create mount root

weed/mount/weedfs.go

@@ -93,6 +93,12 @@ type Option struct {
 	// When true, Flush() returns immediately and data upload + metadata flush happen in background.
 	WritebackCache bool
 
+	// PosixDirNlink enables POSIX-compliant directory nlink counting
+	// (nlink = 2 + number_of_subdirectories). This requires listing
+	// cached directory entries on every stat, which has a performance cost.
+	// When false (default), directories report nlink=2.
+	PosixDirNlink bool
+
 	uniqueCacheDirForRead  string
 	uniqueCacheDirForWrite string
 }

weed/mount/weedfs_attr.go

@@ -1,6 +1,7 @@
 package mount
 
 import (
+	"context"
 	"os"
 	"syscall"
 	"time"
@@ -16,15 +17,21 @@ func (wfs *WFS) GetAttr(cancel <-chan struct{}, input *fuse.GetAttrIn, out *fuse
 	glog.V(4).Infof("GetAttr %v", input.NodeId)
 	if input.NodeId == 1 {
 		wfs.setRootAttr(out)
+		if wfs.option.PosixDirNlink {
+			wfs.applyDirNlink(&out.Attr, util.FullPath(wfs.option.FilerMountRootPath))
+		}
 		return fuse.OK
 	}
 
 	inode := input.NodeId
-	_, _, entry, status := wfs.maybeReadEntry(inode)
+	path, _, entry, status := wfs.maybeReadEntry(inode)
 	if status == fuse.OK {
 		out.AttrValid = 1
 		wfs.setAttrByPbEntry(&out.Attr, inode, entry, true)
 		wfs.applyInMemoryAtime(&out.Attr, inode)
+		if entry.IsDirectory && wfs.option.PosixDirNlink {
+			wfs.applyDirNlink(&out.Attr, path)
+		}
 		return status
 	} else {
 		if fh, found := wfs.fhMap.FindFileHandle(inode); found {
@@ -176,7 +183,7 @@ func (wfs *WFS) setRootAttr(out *fuse.AttrOut) {
 	out.Ctime = now
 	out.Atime = now
 	out.Mode = toSyscallType(os.ModeDir) | uint32(wfs.option.MountMode)
-	out.Nlink = 1
+	out.Nlink = 2
 }
 
 func (wfs *WFS) setAttrByPbEntry(out *fuse.Attr, inode uint64, entry *filer_pb.Entry, calculateSize bool) {
@@ -208,7 +215,9 @@ func (wfs *WFS) setAttrByPbEntry(out *fuse.Attr, inode uint64, entry *filer_pb.E
 	out.Atimensec = uint32(entry.Attributes.MtimeNs)
 	// In-memory atime overlay is applied by the caller via applyInMemoryAtime.
 	out.Mode = toSyscallMode(os.FileMode(entry.Attributes.FileMode))
-	if entry.HardLinkCounter > 0 {
+	if entry.IsDirectory {
+		out.Nlink = 2
+	} else if entry.HardLinkCounter > 0 {
 		out.Nlink = uint32(entry.HardLinkCounter)
 	} else {
 		out.Nlink = 1
@@ -238,7 +247,9 @@ func (wfs *WFS) setAttrByFilerEntry(out *fuse.Attr, inode uint64, entry *filer.E
 		out.Ctimensec = uint32(entry.Attr.Mtime.Nanosecond())
 	}
 	out.Mode = toSyscallMode(entry.Attr.Mode)
-	if entry.HardLinkCounter > 0 {
+	if entry.IsDirectory() {
+		out.Nlink = 2
+	} else if entry.HardLinkCounter > 0 {
 		out.Nlink = uint32(entry.HardLinkCounter)
 	} else {
 		out.Nlink = 1
@@ -306,6 +317,22 @@ func (wfs *WFS) applyInMemoryAtime(out *fuse.Attr, inode uint64) {
 	wfs.atimeMu.Unlock()
 }
 
+// applyDirNlink sets nlink = 2 + number_of_subdirectories for a directory.
+// Only counts from the local metacache to avoid expensive filer queries.
+// When the cache has no entries (e.g. before readdir), keeps nlink=2.
+func (wfs *WFS) applyDirNlink(out *fuse.Attr, dirPath util.FullPath) {
+	var subdirCount uint32
+	wfs.metaCache.ListDirectoryEntries(context.Background(), dirPath, "", false, 100000, func(entry *filer.Entry) (bool, error) {
+		if entry.IsDirectory() {
+			subdirCount++
+		}
+		return true, nil
+	})
+	if subdirCount > 0 {
+		out.Nlink = 2 + subdirCount
+	}
+}
+
 func chmod(existing uint32, mode uint32) uint32 {
 	return existing&^07777 | mode&07777
 }

weed/mount/weedfs_dir_lookup.go

@@ -44,6 +44,10 @@ func (wfs *WFS) Lookup(cancel <-chan struct{}, header *fuse.InHeader, name strin
 
 	wfs.outputFilerEntry(out, inode, localEntry)
 
+	if localEntry.IsDirectory() && wfs.option.PosixDirNlink {
+		wfs.applyDirNlink(&out.Attr, fullFilePath)
+	}
+
 	return fuse.OK
 
 }