Re: [libvirt] [PATCH] snapshot: allow block devices past cgroup

On 05/07/2012 07:00 PM, Eric Blake wrote: > It turns out that when cgroups are enabled, the use of a block device > for a snapshot target was failing with EPERM due to libvirt failing > to add the block device to the cgroup whitelist. See also > https://bugzilla.redhat.com/show_bug.cgi?id=810200 > > * src/qemu/qemu_driver.c > (qemuDomainSnapshotCreateSingleDiskActive) > (qemuDomainSnapshotUndoSingleDiskActive): Account for cgroup. > (qemuDomainSnapshotCreateDiskActive): Update caller. > --- > @@ -9948,8 +9949,15 @@ qemuDomainSnapshotCreateSingleDiskActive(struct qemud_driver *driver, > > if (virDomainLockDiskAttach(driver->lockManager, vm, disk) < 0) > goto cleanup; > + if (cgroup && qemuSetupDiskCgroup(driver, vm, cgroup, disk) < 0) { As far as I can see, you can't get to here if cgroup is NULL.

Technically there's nothing wrong with checking it, but isn't it unnecessary?

> @@ -10084,6 +10095,7 @@ qemuDomainSnapshotCreateDiskActive(virConnectPtr conn, > int thaw = 0; /* 1 if freeze succeeded, -1 if freeze failed */ > bool atomic = (flags & VIR_DOMAIN_SNAPSHOT_CREATE_ATOMIC) != 0; > bool reuse = (flags & VIR_DOMAIN_SNAPSHOT_CREATE_REUSE_EXT) != 0; > + virCgroupPtr cgroup = NULL; > > if (qemuDomainObjBeginJobWithDriver(driver, vm, QEMU_JOB_MODIFY) < 0) > return -1; > @@ -10094,6 +10106,14 @@ qemuDomainSnapshotCreateDiskActive(virConnectPtr conn, > goto endjob; > } > > + if (qemuCgroupControllerActive(driver, VIR_CGROUP_CONTROLLER_DEVICES) && > + virCgroupForDomain(driver->cgroup, vm->def->name, &cgroup, 0)) { > + qemuReportError(VIR_ERR_INTERNAL_ERROR, > + _("Unable to find cgroup for %s"), > + vm->def->name); > + goto endjob; > + } > + By the time you get here, you're guaranteed the cgroup is non-NULL, right?

Also, looking beyond the context provided by git - virCGroupFree() is called in cleanup, which is higher up in the function than end_job, but there are 2 occurrences of goto end_job past where you get the cgroup - if you encountered an error and took either of those goto's, you would end up leaking cgroup.

> @@ -10156,7 +10176,7 @@ qemuDomainSnapshotCreateDiskActive(virConnectPtr conn, > } > } > > - ret = qemuDomainSnapshotCreateSingleDiskActive(driver, vm, > + ret = qemuDomainSnapshotCreateSingleDiskActive(driver, vm, cgroup, So back to the other topic - this is the only place this function is called, and you're guaranteed that cgroup will be non-NULL, so I don't think qemuDomainSnapshotCreateSingleDiskActive() actually needs to check for NULL cgroup.

> @@ -10214,6 +10234,8 @@ qemuDomainSnapshotCreateDiskActive(virConnectPtr conn, > } > > cleanup: > + if (cgroup) > + virCgroupFree(&cgroup); I think this either needs to be moved down to end_job, or the to goto end_job's I mentioned above need to goto cleanup (I think I prefer the former).