Re: [libvirt] [PATCH] blockjob: fix block-stream bandwidth race

On Thu, Apr 26, 2012 at 12:04 AM, Eric Blake <eblake(a)redhat.com&gt; 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 <stefanha(a)linux.vnet.ibm.com&gt;

unsigned long bandwidth,

+ bandwidth *= 1024ULL * 1024ULL; /* Scale MiB to bytes */