fs: empty guest path should bind to / (#1565)

Signed-off-by: Edoardo Vacchi <evacchi@users.noreply.github.com>

internal/sys/fs.go

@@ -413,6 +413,8 @@ func (c *Context) InitFSContext(
 		guestPath := guestPaths[i]
 
 		if StripPrefixesAndTrailingSlash(guestPath) == "" {
+			// Default to bind to '/' when guestPath is effectively empty.
+			guestPath = "/"
 			c.fsc.rootFS = fs
 		}
 		c.fsc.openedFiles.Insert(&FileEntry{

internal/sys/fs_test.go

@@ -3,6 +3,7 @@ package sys
 import (
 	"embed"
 	"errors"
+	"fmt"
 	"io/fs"
 	"os"
 	"path"
@@ -55,8 +56,10 @@ func TestNewFSContext(t *testing.T) {
 		tc := tt
 
 		t.Run(tc.name, func(t *testing.T) {
+			for _, root := range []string{"/", ""} {
+				t.Run(fmt.Sprintf("root = '%s'", root), func(t *testing.T) {
 					c := Context{}
-			err := c.InitFSContext(nil, nil, nil, []fsapi.FS{tc.fs}, []string{"/"}, nil)
+					err := c.InitFSContext(nil, nil, nil, []fsapi.FS{tc.fs}, []string{root}, nil)
 					require.NoError(t, err)
 					fsc := c.fsc
 					defer fsc.Close()
@@ -86,6 +89,9 @@ func TestNewFSContext(t *testing.T) {
 					require.Equal(t, f1, f2)
 				})
 			}
+		})
+
+	}
 }
 
 func TestFSContext_CloseFile(t *testing.T) {