cmd/sharefs: handle mount -t fuse.sharefs

This should have been handled in a custom option parsing function, but that much extra complexity is unnecessary for this edge case. Honestly I do not know why libfuse does not handle this itself.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/sharefs/fuse.go

@@ -314,7 +314,7 @@ func _main(s ...string) (exitCode int) {
 		// hack to keep fuse_parse_cmdline happy in the container
 		mountpoint := C.GoString(opts.mountpoint)
 		pathnameArg := -1
-		for i, arg := range os.Args {
+		for i, arg := range s {
 			if arg == mountpoint {
 				pathnameArg = i
 				break
@@ -324,7 +324,7 @@ func _main(s ...string) (exitCode int) {
 			log.Println("mountpoint must be absolute")
 			return 2
 		}
-		os.Args[pathnameArg] = container.Nonexistent
+		s[pathnameArg] = container.Nonexistent
 	}
 
 	if !parseOpts(&args, &setup, msg.GetLogger()) {
@@ -421,7 +421,7 @@ func _main(s ...string) (exitCode int) {
 		} else {
 			z.Path = a
 		}
-		z.Args = os.Args
+		z.Args = s
 		z.ForwardCancel = true
 		z.SeccompPresets |= std.PresetStrict
 		z.ParentPerm = 0700

cmd/sharefs/main.go

@@ -3,14 +3,29 @@ package main
 import (
 	"log"
 	"os"
+	"slices"
 )
 
 // sharefsName is the prefix used by log.std in the sharefs process.
 const sharefsName = "sharefs"
 
+// handleMountArgs returns an alternative, libfuse-compatible args slice for
+// args passed by mount -t fuse.sharefs [options] sharefs <mountpoint>.
+//
+// In this case, args always has a length of 5 with index 0 being what comes
+// after "fuse." in the filesystem type, 1 is the uninterpreted string passed
+// to mount (sharefsName is used as the magic string to enable this hack),
+// 2 is passed through to libfuse as mountpoint, and 3 is always "-o".
+func handleMountArgs(args []string) []string {
+	if len(args) == 5 && args[1] == sharefsName && args[3] == "-o" {
+		return []string{sharefsName, args[2], "-o", args[4]}
+	}
+	return slices.Clone(args)
+}
+
 func main() {
 	log.SetFlags(0)
 	log.SetPrefix(sharefsName + ": ")
 
-	os.Exit(_main(os.Args...))
+	os.Exit(_main(handleMountArgs(os.Args)...))
 }

cmd/sharefs/main_test.go

@@ -0,0 +1,29 @@
+package main
+
+import (
+	"slices"
+	"testing"
+)
+
+func TestHandleMountArgs(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		args []string
+		want []string
+	}{
+		{"nil", nil, nil},
+		{"passthrough", []string{"sharefs", "-V"}, []string{"sharefs", "-V"}},
+		{"replace", []string{"/sbin/sharefs", "sharefs", "/sdcard", "-o", "rw"}, []string{"sharefs", "/sdcard", "-o", "rw"}},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got := handleMountArgs(tc.args); !slices.Equal(got, tc.want) {
+				t.Errorf("handleMountArgs: %q, want %q", got, tc.want)
+			}
+		})
+	}
+}