package fusefrontend

import (
	"golang.org/x/sys/unix"

	"github.com/rfjakob/gocryptfs/v2/internal/syscallcompat"
)

// SharedStorageLock conveniently wraps F_OFD_SETLKW
// See https://man7.org/linux/man-pages/man2/fcntl.2.html -> "Open file description locks (non-POSIX)"
//
// lkType is one of:
// * unix.F_RDLCK (shared read lock)
// * unix.F_WRLCK (exclusive write lock)
// * unix.F_UNLCK (unlock)
//
// This function is a no-op if args.SharedStorage == false.
func (f *File) LockSharedStorage(lkType int16, lkStart int64, lkLen int64) error {
	if !f.rootNode.args.SharedStorage {
		return nil
	}
	lk := unix.Flock_t{
		Type:   lkType,
		Whence: unix.SEEK_SET,
		Start:  lkStart,
		Len:    lkLen,
	}
	return unix.FcntlFlock(uintptr(f.intFd()), syscallcompat.F_OFD_SETLKW, &lk)
}