Refactor p9.ExtractErrno() into TryExtractErrno().

TryExtractErrno() additionally reports whether the error extraction was
successful.

PiperOrigin-RevId: 684532198

pkg/p9/handlers.go

@@ -30,36 +30,43 @@ import (
 	"gvisor.dev/gvisor/pkg/log"
 )
 
-// ExtractErrno extracts a unix.Errno from a error, best effort.
+// ExtractErrno extracts a unix.Errno from an error, best effort.
 func ExtractErrno(err error) unix.Errno {
+	errno, _ := TryExtractErrno(err)
+	return errno
+}
+
+// TryExtractErrno extracts a unix.Errno from an error, and reports whether it
+// was successful. If unsuccessful, the returned errno is EIO.
+func TryExtractErrno(err error) (unix.Errno, bool) {
 	switch err {
 	case os.ErrNotExist:
-		return unix.ENOENT
+		return unix.ENOENT, true
 	case os.ErrExist:
-		return unix.EEXIST
+		return unix.EEXIST, true
 	case os.ErrPermission:
-		return unix.EACCES
+		return unix.EACCES, true
 	case os.ErrInvalid:
-		return unix.EINVAL
+		return unix.EINVAL, true
 	}
 
 	// Attempt to unwrap.
 	switch e := err.(type) {
 	case *errors.Error:
-		return linuxerr.ToUnix(e)
+		return linuxerr.ToUnix(e), true
 	case unix.Errno:
-		return e
+		return e, true
 	case *os.PathError:
-		return ExtractErrno(e.Err)
+		return TryExtractErrno(e.Err)
 	case *os.SyscallError:
-		return ExtractErrno(e.Err)
+		return TryExtractErrno(e.Err)
 	case *os.LinkError:
-		return ExtractErrno(e.Err)
+		return TryExtractErrno(e.Err)
 	}
 
 	// Default case.
 	log.Warningf("unknown error: %v", err)
-	return unix.EIO
+	return unix.EIO, false
 }
 
 // newErr returns a new error message from an error.