On 02/20/2013 04:51 AM, Guannan Ren wrote:
> The max value of number of cpus to compute(id) should not
> be equal or greater than max cpu number.
> The bug ocurrs when id value is equal to max cpu number which
s/ocurrs/occurs/
> leads to the off-by-one error in the following for loop.
>
> # virsh cpu-stats guest --start 1
> error: Failed to virDomainGetCPUStats()
>
> error: internal error cpuacct parse error
> ---
> src/qemu/qemu_driver.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
> /* number of cpus to compute */
> - id = max_id;
> -
> - if (max_id - start_cpu > ncpus - 1)
The old code was trying to avoid the possibility of integer overflow, by
only using subtraction (src/libvirt.c already ensured we have
non-negative values, but not necessarily that the sum of two positive
values won't wrap around to negative).
> + if ((start_cpu + ncpus) >= max_id)
The new code is not as careful, and has redundant ().
ACK if you change this to the equivalent:
if (start_cpu >= max_id - ncpus)
> + id = max_id - 1;
> + else
> id = start_cpu + ncpus - 1;
>
> for (i = 0; i <= id; i++) {
>
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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