Re: [libvirt] [PATCH v3 03/13] security: Always spawn process for transactions

On 10/17/18 5:06 AM, Michal Privoznik wrote: Based slightly upon the KVM Forum presentation detailing some performance issues related to the usage of virFork for virQEMUCapsIsValid and calls to virFileAccessibleAs: https://www.redhat.com/archives/libvir-list/2018-October/msg01333.html Given that this patch would thus virFork "always", what kind of impact could that have? Have you been able to do any performance profiling? What would cause a single round of SELinux & DAC settings? I know in an earlier patch I wasn't including performance of virFork because I believed that the only time it would be used would be for metadata locking when (re)labeling would be batched and for that case the "one off" virFork would seem reasonable. Since it is possible to turn off the NS code and thus go through the direct call, I think there's "room for it" here too for those singular cases we could use "pid == -1" to indicate direct calls without virFork and "pid == 0" to batch together calls using virProcessRunInFork. That way when you *know* you are batching together more than singular changes, then the caller can choose to run in a fork knowing the possible performance penalty, but with the benefits. For those that are batched we're stuck, but my memory on all the metadata locking paths is fuzzy already. What's here does work, but after that KVM Forum preso I guess we definitely need to pay attention to areas that can be perf bottlenecks for paths that may be really common. Having a way to disable or avoid virFork is something we may just need to have. I'm willing to be convinced otherwise - I'm just "wary" now. The function description would need an update way to describe this @pid usage which differs from the current description. I think I've previously disclosed my dislike of the format, why not: if (pid > 0) { rc = virProcessRunInMountNamespace(pid, ...); } else { if (pid == -1) rc = virSecurityDACTransactionRun(-pid, list); else rc = virProcessRunInFork(virSecurityDACTransactionRun, list)); } if (rc < 0) goto cleanup; to me that's a lot cleaner and doesn't involve trying to look at multiple if statements with ||'s. ditto. John