Misc fixes to make stat_test pass (almost)

The only test failing now requires socket which is not
available in VFS2 yet.

Updates #1198

PiperOrigin-RevId: 302976572

2 files changed, 49 insertions, 8 deletions

diff --git a/pkg/sentry/fsimpl/gofer/filesystem.go b/pkg/sentry/fsimpl/gofer/filesystem.go
index 38e4cdbc5..26b492185 100644
--- a/pkg/sentry/fsimpl/gofer/filesystem.go
+++ b/pkg/sentry/fsimpl/gofer/filesystem.go
@@ -454,6 +454,9 @@ func (fs *filesystem) unlinkAt(ctx context.Context, rp *vfs.ResolvingPath, dir b
 	}
 	if fs.opts.interop != InteropModeShared {
 		parent.touchCMtime(ctx)
+		if dir {
+			parent.decLinks()
+		}
 		parent.cacheNegativeChildLocked(name)
 		parent.dirents = nil
 	}
@@ -569,8 +572,13 @@ func (fs *filesystem) LinkAt(ctx context.Context, rp *vfs.ResolvingPath, vd vfs.
 func (fs *filesystem) MkdirAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.MkdirOptions) error {
 	return fs.doCreateAt(ctx, rp, true /* dir */, func(parent *dentry, name string) error {
 		creds := rp.Credentials()
-		_, err := parent.file.mkdir(ctx, name, (p9.FileMode)(opts.Mode), (p9.UID)(creds.EffectiveKUID), (p9.GID)(creds.EffectiveKGID))
-		return err
+		if _, err := parent.file.mkdir(ctx, name, (p9.FileMode)(opts.Mode), (p9.UID)(creds.EffectiveKUID), (p9.GID)(creds.EffectiveKGID)); err != nil {
+			return err
+		}
+		if fs.opts.interop != InteropModeShared {
+			parent.incLinks()
+		}
+		return nil
 	})
 }
 
@@ -962,6 +970,10 @@ func (fs *filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, oldPa
 		oldParent.dirents = nil
 		delete(newParent.negativeChildren, newName)
 		newParent.dirents = nil
+		if renamed.isDir() {
+			oldParent.decLinks()
+			newParent.incLinks()
+		}
 	}
 	vfsObj.CommitRenameReplaceDentry(&renamed.vfsd, &newParent.vfsd, newName, replacedVFSD)
 	return nil
diff --git a/pkg/sentry/fsimpl/gofer/gofer.go b/pkg/sentry/fsimpl/gofer/gofer.go
index 999485492..13928ce36 100644
--- a/pkg/sentry/fsimpl/gofer/gofer.go
+++ b/pkg/sentry/fsimpl/gofer/gofer.go
@@ -485,6 +485,11 @@ type dentry struct {
 	// locked to mutate it).
 	size uint64
 
+	// nlink counts the number of hard links to this dentry. It's updated and
+	// accessed using atomic operations. It's not protected by metadataMu like the
+	// other metadata fields.
+	nlink uint32
+
 	mapsMu sync.Mutex
 
 	// If this dentry represents a regular file, mappings tracks mappings of
@@ -604,6 +609,9 @@ func (fs *filesystem) newDentry(ctx context.Context, file p9file, qid p9.QID, ma
 	if mask.BTime {
 		d.btime = dentryTimestampFromP9(attr.BTimeSeconds, attr.BTimeNanoSeconds)
 	}
+	if mask.NLink {
+		d.nlink = uint32(attr.NLink)
+	}
 	d.vfsd.Init(d)
 
 	fs.syncMu.Lock()
@@ -645,6 +653,9 @@ func (d *dentry) updateFromP9Attrs(mask p9.AttrMask, attr *p9.Attr) {
 	if mask.BTime {
 		atomic.StoreInt64(&d.btime, dentryTimestampFromP9(attr.BTimeSeconds, attr.BTimeNanoSeconds))
 	}
+	if mask.NLink {
+		atomic.StoreUint32(&d.nlink, uint32(attr.NLink))
+	}
 	if mask.Size {
 		d.dataMu.Lock()
 		atomic.StoreUint64(&d.size, attr.Size)
@@ -687,10 +698,7 @@ func (d *dentry) fileType() uint32 {
 func (d *dentry) statTo(stat *linux.Statx) {
 	stat.Mask = linux.STATX_TYPE | linux.STATX_MODE | linux.STATX_NLINK | linux.STATX_UID | linux.STATX_GID | linux.STATX_ATIME | linux.STATX_MTIME | linux.STATX_CTIME | linux.STATX_INO | linux.STATX_SIZE | linux.STATX_BLOCKS | linux.STATX_BTIME
 	stat.Blksize = atomic.LoadUint32(&d.blockSize)
-	stat.Nlink = 1
-	if d.isDir() {
-		stat.Nlink = 2
-	}
+	stat.Nlink = atomic.LoadUint32(&d.nlink)
 	stat.UID = atomic.LoadUint32(&d.uid)
 	stat.GID = atomic.LoadUint32(&d.gid)
 	stat.Mode = uint16(atomic.LoadUint32(&d.mode))
@@ -703,7 +711,7 @@ func (d *dentry) statTo(stat *linux.Statx) {
 	stat.Btime = statxTimestampFromDentry(atomic.LoadInt64(&d.btime))
 	stat.Ctime = statxTimestampFromDentry(atomic.LoadInt64(&d.ctime))
 	stat.Mtime = statxTimestampFromDentry(atomic.LoadInt64(&d.mtime))
-	// TODO(jamieliu): device number
+	// TODO(gvisor.dev/issue/1198): device number
 }
 
 func (d *dentry) setStat(ctx context.Context, creds *auth.Credentials, stat *linux.Statx, mnt *vfs.Mount) error {
@@ -1094,6 +1102,26 @@ func (d *dentry) ensureSharedHandle(ctx context.Context, read, write, trunc bool
 	return nil
 }
 
+// incLinks increments link count.
+//
+// Preconditions: d.nlink != 0 && d.nlink < math.MaxUint32.
+func (d *dentry) incLinks() {
+	v := atomic.AddUint32(&d.nlink, 1)
+	if v < 2 {
+		panic(fmt.Sprintf("dentry.nlink is invalid (was 0 or overflowed): %d", v))
+	}
+}
+
+// decLinks decrements link count.
+//
+// Preconditions: d.nlink > 1.
+func (d *dentry) decLinks() {
+	v := atomic.AddUint32(&d.nlink, ^uint32(0))
+	if v == 0 {
+		panic(fmt.Sprintf("dentry.nlink must be greater than 0: %d", v))
+	}
+}
+
 // fileDescription is embedded by gofer implementations of
 // vfs.FileDescriptionImpl.
 type fileDescription struct {
@@ -1112,7 +1140,8 @@ func (fd *fileDescription) dentry() *dentry {
 // Stat implements vfs.FileDescriptionImpl.Stat.
 func (fd *fileDescription) Stat(ctx context.Context, opts vfs.StatOptions) (linux.Statx, error) {
 	d := fd.dentry()
-	if d.fs.opts.interop == InteropModeShared && opts.Mask&(linux.STATX_MODE|linux.STATX_UID|linux.STATX_GID|linux.STATX_ATIME|linux.STATX_MTIME|linux.STATX_CTIME|linux.STATX_SIZE|linux.STATX_BLOCKS|linux.STATX_BTIME) != 0 && opts.Sync != linux.AT_STATX_DONT_SYNC {
+	const validMask = uint32(linux.STATX_MODE | linux.STATX_UID | linux.STATX_GID | linux.STATX_ATIME | linux.STATX_MTIME | linux.STATX_CTIME | linux.STATX_SIZE | linux.STATX_BLOCKS | linux.STATX_BTIME)
+	if d.fs.opts.interop == InteropModeShared && opts.Mask&(validMask) != 0 && opts.Sync != linux.AT_STATX_DONT_SYNC {
 		// TODO(jamieliu): Use specialFileFD.handle.file for the getattr if
 		// available?
 		if err := d.updateFromGetattr(ctx); err != nil {