Some examples relate to performing application-defined object logging through a file system journal. In an example, a file system may determine during execution of an operation for an application whether a callback function is specified for the operation. In response to the determination, file system may invoke the callback function. File system may receive an object defined by the application. File system may link a copy of the object with a file system transaction associated with the operation in a journal of file system. File system may determine whether file system transaction is committed. In response to the determination, file system may write a copy of the object from the journal to an event log file. File system may allow the application to determine whether file system transaction is committed by enabling access to the event log file.