Re: [libvirt] [RFC] Simplifying usage of {Enter, Exit}Monitor and {Begin/End}Job

Hi all. Looking at the qemu driver code, we have a lot of code with the following pattern: if (doSomething() < 0) goto cleanup; if (qemuDomainObjBeginJob() < 0) goto cleanup; if (doSomethingElse() < 0) goto endjob; qemuDomainObjEnterMonitor(); if (qemuMonitorSomething() < 0) { qemuDomainObjExitMonitor(); goto endjob; } if (qemuMonitorSomethingElse() < 0) { qemuDomainObjExitMonitor(); goto endjob; } if (qemuDomainObjExitMonitor() < 0) goto endjob; ... ret = 0; endjob: qemuDomainObjEndJob(); cleanup: ... return ret; Sometimes qemuDomainObjExitMonitor is in its own label instead of being explicitly called on every single error path. Sometimes qemuDomainObjEndJob is called explicitly followed by goto cleanup. In either case, it's pretty easy to get this wrong. It's too easy to jump to a wrong label (especially when moving code around) or forget to call the appropriate exit function before jumping to a label. So what if we make the code more robust by changing who needs to track whether we are in a monitor or have a job. Now it's the caller that tracks it while I think we could teach the job/monitor APIs themselves to track the state: bool inJob = false; bool inMonitor = false; if (doSomething() < 0) goto cleanup; if (qemuDomainObjBeginJob(..., &inJob) < 0) goto cleanup; if (doSomethingElse() < 0) goto cleanup; qemuDomainObjEnterMonitor(..., &inMonitor); if (qemuMonitorSomething() < 0) goto cleanup; if (qemuMonitorSomethingElse() < 0) goto cleanup; if (qemuDomainObjExitMonitor(..., &inMonitor) < 0) goto cleanup; ... ret = 0; cleanup: if (qemuDomainObjExitMonitor(..., &inMonitor) < 0) ret = -1; qemuDomainObjEndJob(..., &inJob); ... return ret; It's not a lot shorter or longer but it saves us from jumping to different labels and it makes sure we always exit the monitor and end the job. So is it worth the effort or do you thing it's even worse than before or do you have any other ideas?

Thanks, Jirka -- libvir-list mailing list libvir-list(a)redhat.com https://www.redhat.com/mailman/listinfo/libvir-list