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