On 03/07/2012 12:18 AM, Osier Yang wrote:
On 03/07/2012 02:46 PM, Osier Yang wrote:
On 03/07/2012 12:48 PM, Eric Blake wrote:
The RPC code assumed that the array returned by the driver would be fully populated; that is, ncpus on entry resulted in ncpus * return value on exit. However, while we don't support holes in the middle of ncpus, we do want to permit the case of ncpus on entry being longer than the array returned by the driver (that is, it should be safe for the caller to pass ncpus=128 on entry, and the driver will stop populating the array when it hits max_id).
/* The remote side did not send back any zero entries, so we have - * to expand things back into a possibly sparse array. + * to expand things back into a possibly sparse array, where the + * tail of the array may be omitted. */ memset(params, 0, sizeof(*params) * nparams * ncpus); + ncpus = ret.params.params_len / ret.nparams; for (cpu = 0; cpu< ncpus; cpu++) { int tmp = nparams; remote_typed_param *stride =&ret.params.params_val[cpu * ret.nparams];
Make sense, and ACK.
I realized that qemu_driver.c also needs this memset to guarantee that unused slots are returned empty on success.
But do we want to add document to declare the returned array will be truncated among the API implementation. Not neccessary though.
Perhaps something like:
* whole). Otherwise, @start_cpu represents which cpu to start * with, and @ncpus represents how many consecutive processors to * query, with statistics attributable per processor (such as - * per-cpu usage). + * per-cpu usage). If @ncpus is larger than the number of host + * CPUs, the exceeded one(s) will be just ignored.
Good idea. Here's what I squashed in before pushing: diff --git i/src/libvirt.c w/src/libvirt.c index d98741b..39ebb52 100644 --- i/src/libvirt.c +++ w/src/libvirt.c @@ -18534,7 +18534,9 @@ error: * whole). Otherwise, @start_cpu represents which cpu to start * with, and @ncpus represents how many consecutive processors to * query, with statistics attributable per processor (such as - * per-cpu usage). + * per-cpu usage). If @ncpus is larger than the number of cpus + * available to query, then the trailing part of the array will + * be unpopulated. * * The remote driver imposes a limit of 128 @ncpus and 16 @nparams; * the number of parameters per cpu should not exceed 16, but if you @@ -18579,8 +18581,10 @@ error: * number of populated @params, unless @ncpus was 1; and may be * less than @nparams). The populated parameters start at each * stride of @nparams, which means the results may be discontiguous; - * any unpopulated parameters will be zeroed on success. The caller - * is responsible for freeing any returned string parameters. + * any unpopulated parameters will be zeroed on success (this includes + * skipped elements if @nparams is too large, and tail elements if + * @ncpus is too large). The caller is responsible for freeing any + * returned string parameters. */ int virDomainGetCPUStats(virDomainPtr domain, virTypedParameterPtr params, diff --git i/src/qemu/qemu_driver.c w/src/qemu/qemu_driver.c index 538a419..ddb381a 100644 --- i/src/qemu/qemu_driver.c +++ w/src/qemu/qemu_driver.c @@ -12162,6 +12162,7 @@ qemuDomainGetPercpuStats(virDomainPtr domain, if (virCgroupGetCpuacctPercpuUsage(group, &buf)) goto cleanup; pos = buf; + memset(params, 0, nparams * ncpus); if (max_id - start_cpu > ncpus - 1) max_id = start_cpu + ncpus - 1; -- Eric Blake eblake@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org