[lisa] Plumb lisafs through runsc.

lisafs is only supported in VFS2. Added a runsc flag which enables lisafs.
When the flag is enabled, the gofer process and the client communicate using
lisafs protocol instead of 9P.

Added a filesystem option in fsimpl/gofer which indicates if lisafs is being
used. That will be used to gate lisafs on the gofer client.

Note that this change does not make the gofer client use lisafs just yet.

Updates #5465

PiperOrigin-RevId: 397917844

2 files changed, 16 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/gofer/filesystem.go b/pkg/sentry/fsimpl/gofer/filesystem.go
index 00228c469..9d943bd4a 100644
--- a/pkg/sentry/fsimpl/gofer/filesystem.go
+++ b/pkg/sentry/fsimpl/gofer/filesystem.go
@@ -1612,6 +1612,9 @@ func (fs *filesystem) MountOptions() string {
 	if fs.opts.overlayfsStaleRead {
 		optsKV = append(optsKV, mopt{moptOverlayfsStaleRead, nil})
 	}
+	if fs.opts.lisaEnabled {
+		optsKV = append(optsKV, mopt{moptLisafs, nil})
+	}
 
 	opts := make([]string, 0, len(optsKV))
 	for _, opt := range optsKV {
diff --git a/pkg/sentry/fsimpl/gofer/gofer.go b/pkg/sentry/fsimpl/gofer/gofer.go
index 43440ec19..13971d086 100644
--- a/pkg/sentry/fsimpl/gofer/gofer.go
+++ b/pkg/sentry/fsimpl/gofer/gofer.go
@@ -83,6 +83,7 @@ const (
 	moptForcePageCache         = "force_page_cache"
 	moptLimitHostFDTranslation = "limit_host_fd_translation"
 	moptOverlayfsStaleRead     = "overlayfs_stale_read"
+	moptLisafs                 = "lisafs"
 )
 
 // Valid values for the "cache" mount option.
@@ -214,6 +215,10 @@ type filesystemOptions struct {
 	// way that application FDs representing "special files" such as sockets
 	// do. Note that this disables client caching and mmap for regular files.
 	regularFilesUseSpecialFileFD bool
+
+	// lisaEnabled indicates whether the client will use lisafs protocol to
+	// communicate with the server instead of 9P.
+	lisaEnabled bool
 }
 
 // InteropMode controls the client's interaction with other remote filesystem
@@ -427,6 +432,14 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 		delete(mopts, moptOverlayfsStaleRead)
 		fsopts.overlayfsStaleRead = true
 	}
+	if lisafs, ok := mopts[moptLisafs]; ok {
+		delete(mopts, moptLisafs)
+		fsopts.lisaEnabled, err = strconv.ParseBool(lisafs)
+		if err != nil {
+			ctx.Warningf("gofer.FilesystemType.GetFilesystem: invalid lisafs option: %s", lisafs)
+			return nil, nil, linuxerr.EINVAL
+		}
+	}
 	// fsopts.regularFilesUseSpecialFileFD can only be enabled by specifying
 	// "cache=none".