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, 54 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/fuse/directory.go b/pkg/sentry/fsimpl/fuse/directory.go
index 44d41712a..8c59680e8 100644
--- a/pkg/sentry/fsimpl/fuse/directory.go
+++ b/pkg/sentry/fsimpl/fuse/directory.go
@@ -15,7 +15,12 @@
 package fuse
 
 import (
+	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/usermem"
@@ -49,3 +54,52 @@ func (directoryFD) PWrite(ctx context.Context, src usermem.IOSequence, offset in
 func (directoryFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
 	return 0, syserror.EISDIR
 }
+
+// IterDirents implements FileDescriptionImpl.IterDirents.
+func (dir *directoryFD) IterDirents(ctx context.Context, callback vfs.IterDirentsCallback) error {
+	fusefs := dir.inode().fs
+	task, creds := kernel.TaskFromContext(ctx), auth.CredentialsFromContext(ctx)
+
+	in := linux.FUSEReadIn{
+		Fh:     dir.Fh,
+		Offset: uint64(atomic.LoadInt64(&dir.off)),
+		Size:   linux.FUSE_PAGE_SIZE,
+		Flags:  dir.statusFlags(),
+	}
+
+	/// TODO(gVisor.dev/issue/3404): Support FUSE_READDIRPLUS.
+	req, err := fusefs.conn.NewRequest(creds, uint32(task.ThreadID()), dir.inode().NodeID, linux.FUSE_READDIR, &in)
+	if err != nil {
+		return err
+	}
+
+	res, err := fusefs.conn.Call(task, req)
+	if err != nil {
+		return err
+	}
+	if err := res.Error(); err != nil {
+		return err
+	}
+
+	var out linux.FUSEDirents
+	if err := res.UnmarshalPayload(&out); err != nil {
+		return err
+	}
+
+	for _, fuseDirent := range out.Dirents {
+		nextOff := int64(fuseDirent.Meta.Off) + 1
+		dirent := vfs.Dirent{
+			Name:    fuseDirent.Name,
+			Type:    uint8(fuseDirent.Meta.Type),
+			Ino:     fuseDirent.Meta.Ino,
+			NextOff: nextOff,
+		}
+
+		if err := callback.Handle(dirent); err != nil {
+			return err
+		}
+		atomic.StoreInt64(&dir.off, nextOff)
+	}
+
+	return nil
+}