On 04/26/2012 03:05 AM, Stefan Hajnoczi wrote: > On Thu, Apr 26, 2012 at 12:04 AM, Eric Blake <ebl...@redhat.com> wrote: >> With RHEL 6.2, virDomainBlockPull(dom, dev, bandwidth, 0) has a race >> with non-zero bandwidth: there is a window between the block_stream >> and block_job_set_speed monitor commands where an unlimited amount >> of data was let through, defeating the point of a throttle. >> >> This race was first identified in commit a9d3495e, and libvirt was >> able to reduce the size of the window for that race. In the meantime, >> the qemu developers decided to fix things properly; per this message: >> https://lists.gnu.org/archive/html/qemu-devel/2012-04/msg03793.html >> the fix will be in qemu 1.1, and changes block-job-set-speed to use >> a different parameter name, as well as adding a new optional parameter >> to block-stream, which eliminates the race altogether. >> >> Since our documentation already mentioned that we can refuse a non-zero >> bandwidth for some hypervisors, I think the best solution is to do >> just that for RHEL 6.2 qemu, so that the race is obvious to the user. >> Meanwhile the code must be fixed to honor actual qemu 1.1 naming. >> >> * src/qemu/qemu_monitor.h (enum BLOCK_JOB_CMD): Drop unused value. >> * src/qemu/qemu_driver.c (qemuDomainBlockJobImpl): Reject >> bandwidth during pull with too-old qemu. >> * src/qemu/qemu_monitor_json.c (qemuMonitorJSONBlockJob): Support >> difference between RHEL 6.2 and qemu 1.1 block pull. >> * src/libvirt.c (virDomainBlockPull, virDomainBlockRebase): >> Document this. >> --- >> src/libvirt.c | 6 +++- >> src/qemu/qemu_driver.c | 8 ++++-- >> src/qemu/qemu_monitor.h | 3 +- >> src/qemu/qemu_monitor_json.c | 53 >> +++++++++++++++++++++++------------------ >> 4 files changed, 40 insertions(+), 30 deletions(-) > > Reviewed-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com>
Thanks. However, I found a bug: > unsigned long bandwidth, ... > + bandwidth *= 1024ULL * 1024ULL; /* Scale MiB to bytes */ This can overflow, and silently wrap around. v2 coming up. -- Eric Blake ebl...@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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