fuse: Implement IterDirents for directory file description

Fixes #3255.

This change adds support for IterDirents. You can now use `ls` in
the FUSE sandbox.

Co-authored-by: Craig Chi <craigchi@google.com>

1 files changed, 127 insertions, 4 deletions

diff --git a/pkg/abi/linux/fuse.go b/pkg/abi/linux/fuse.go
index c75debb8c..e7b5f45de 100644
--- a/pkg/abi/linux/fuse.go
+++ b/pkg/abi/linux/fuse.go
@@ -14,7 +14,10 @@
 
 package linux
 
-import "gvisor.dev/gvisor/tools/go_marshal/marshal"
+import (
+	"gvisor.dev/gvisor/tools/go_marshal/marshal"
+	"gvisor.dev/gvisor/tools/go_marshal/primitive"
+)
 
 // +marshal
 type FUSEOpcode uint32
@@ -186,9 +189,9 @@ const (
 
 // Constants relevant to FUSE operations.
 const (
-	FUSE_NAME_MAX     = 1024
-	FUSE_PAGE_SIZE    = 4096
-	FUSE_DIRENT_ALIGN = 8
+	FUSE_NAME_MAX       = 1024
+	FUSE_PAGE_SIZE      = 4096
+	FUSE_DIRENT_ALIGN   = 8
 )
 
 // FUSEInitIn is the request sent by the kernel to the daemon,
@@ -595,3 +598,123 @@ func (r *FUSERmDirIn) SizeBytes() int {
 func (r *FUSERmDirIn) UnmarshalUnsafe(src []byte) {
 	r.Name = string(src)
 }
+
+// FUSEDirents is a list of Dirents received from the FUSE daemon server.
+// It is used for FUSE_READDIR.
+//
+// Dynamically-sized objects cannot be marshalled.
+type FUSEDirents struct {
+	marshal.StubMarshallable
+
+	Dirents []*FUSEDirent
+}
+
+// FUSEDirent is a Dirent received from the FUSE daemon server.
+// It is used for FUSE_READDIR.
+//
+// Dynamically-sized objects cannot be marshalled.
+type FUSEDirent struct {
+	marshal.StubMarshallable
+
+	// Meta contains all the static fields of FUSEDirent.
+	Meta FUSEDirentMeta
+
+	// Name is the filename of the dirent.
+	Name string
+}
+
+// FUSEDirentMeta contains all the static fields of FUSEDirent.
+// It is used for FUSE_READDIR.
+//
+// +marshal
+type FUSEDirentMeta struct {
+	// Inode of the dirent.
+	Ino uint64
+
+	// Offset of the dirent.
+	Off uint64
+
+	// NameLen is the length of the dirent name.
+	NameLen uint32
+
+	// Type of the dirent.
+	Type uint32
+}
+
+// MarshalUnsafe serializes FUSEDirents to the dst buffer.
+func (r *FUSEDirents) MarshalUnsafe(dst []byte) {
+	for _, dirent := range r.Dirents {
+		dirent.MarshalUnsafe(dst)
+		dst = dst[dirent.SizeBytes():]
+	}
+}
+
+// SizeBytes is the size of the memory representation of FUSEDirents.
+func (r *FUSEDirents) SizeBytes() int {
+	var sizeBytes int
+	for _, dirent := range r.Dirents {
+		sizeBytes += dirent.SizeBytes()
+	}
+
+	return sizeBytes
+}
+
+// UnmarshalUnsafe deserializes FUSEDirents from the src buffer.
+func (r *FUSEDirents) UnmarshalUnsafe(src []byte) {
+	for {
+		if len(src) <= (*FUSEDirentMeta)(nil).SizeBytes() {
+			break
+		}
+
+		// Its unclear how many dirents there are in src. Each dirent is dynamically
+		// sized and so we can't make assumptions about how many dirents we can allocate.
+		if r.Dirents == nil {
+			r.Dirents = make([]*FUSEDirent, 0)
+		}
+
+		// We have to allocate a struct for each dirent - there must be a better way
+		// to do this. Linux allocates 1 page to store all the dirents and then
+		// simply reads them from the page.
+		var dirent FUSEDirent
+		dirent.UnmarshalUnsafe(src)
+		r.Dirents = append(r.Dirents, &dirent)
+
+		src = src[dirent.SizeBytes():]
+	}
+}
+
+// MarshalUnsafe serializes FUSEDirent to the dst buffer.
+func (r *FUSEDirent) MarshalUnsafe(dst []byte) {
+	r.Meta.MarshalUnsafe(dst)
+	dst = dst[r.Meta.SizeBytes():]
+
+	name := primitive.ByteSlice(r.Name)
+	name.MarshalUnsafe(dst)
+}
+
+// SizeBytes is the size of the memory representation of FUSEDirent.
+func (r *FUSEDirent) SizeBytes() int {
+	dataSize := r.Meta.SizeBytes() + len(r.Name)
+
+	// Each Dirent must be padded such that its size is a multiple
+	// of FUSE_DIRENT_ALIGN. Similar to the fuse dirent alignment
+	// in linux/fuse.h.
+	return (dataSize + (FUSE_DIRENT_ALIGN - 1)) & ^(FUSE_DIRENT_ALIGN - 1)
+}
+
+// UnmarshalUnsafe deserializes FUSEDirent from the src buffer.
+func (r *FUSEDirent) UnmarshalUnsafe(src []byte) {
+	r.Meta.UnmarshalUnsafe(src)
+	src = src[r.Meta.SizeBytes():]
+
+	if r.Meta.NameLen > FUSE_NAME_MAX {
+		// The name is too long and therefore invalid. We don't
+		// need to unmarshal the name since it'll be thrown away.
+		return
+	}
+
+	buf := make([]byte, r.Meta.NameLen)
+	name := primitive.ByteSlice(buf)
+	name.UnmarshalUnsafe(src[:r.Meta.NameLen])
+	r.Name = string(name)
+}