Re: [Xen-devel] [PATCH v3 1/8] golang/xenlight: Don't try to marshall zero-length arrays in fromC

2020-01-21 Thread George Dunlap 
On 1/20/20 11:39 PM, Nick Rosbrook wrote:
>  Sorry I didn't catch this the first time around, but:
> 
>> diff --git a/tools/golang/xenlight/helpers.gen.go 
>> b/tools/golang/xenlight/helpers.gen.go
>> index b9a7e828a0..889807d928 100644
>> --- a/tools/golang/xenlight/helpers.gen.go
>> +++ b/tools/golang/xenlight/helpers.gen.go
>> @@ -623,12 +623,14 @@ func (x *SchedParams) toC(xc *C.libxl_sched_params) 
>> (err error) {
>>
>>  func (x *VcpuSchedParams) fromC(xc *C.libxl_vcpu_sched_params) error {
>> x.Sched = Scheduler(xc.sched)
>> -   numVcpus := int(xc.num_vcpus)
>> -   cVcpus := (*[1 << 
>> 28]C.libxl_sched_params)(unsafe.Pointer(xc.vcpus))[:numVcpus:numVcpus]
>> -   x.Vcpus = make([]SchedParams, numVcpus)
>> -   for i, v := range cVcpus {
>> -   if err := x.Vcpus[i].fromC(); err != nil {
>> -   return err
>> +   x.Vcpus = nil
>> +   if numVcpus := int(xc.num_vcpus); numVcpus > 0 {
> 
> 
> Since `numX` is now scoped to this if block, we could probably just
> use `n` or similar and then drop `golenvar` from
> `xenlight_golang_array_fromC`. It would remove some pretty ugly
> variable names from the generated code :)

Yes, that looks good.

 -George

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Re: [Xen-devel] [PATCH v3 1/8] golang/xenlight: Don't try to marshall zero-length arrays in fromC

2020-01-20 Thread Nick Rosbrook 
 Sorry I didn't catch this the first time around, but:

> diff --git a/tools/golang/xenlight/helpers.gen.go 
> b/tools/golang/xenlight/helpers.gen.go
> index b9a7e828a0..889807d928 100644
> --- a/tools/golang/xenlight/helpers.gen.go
> +++ b/tools/golang/xenlight/helpers.gen.go
> @@ -623,12 +623,14 @@ func (x *SchedParams) toC(xc *C.libxl_sched_params) 
> (err error) {
>
>  func (x *VcpuSchedParams) fromC(xc *C.libxl_vcpu_sched_params) error {
> x.Sched = Scheduler(xc.sched)
> -   numVcpus := int(xc.num_vcpus)
> -   cVcpus := (*[1 << 
> 28]C.libxl_sched_params)(unsafe.Pointer(xc.vcpus))[:numVcpus:numVcpus]
> -   x.Vcpus = make([]SchedParams, numVcpus)
> -   for i, v := range cVcpus {
> -   if err := x.Vcpus[i].fromC(); err != nil {
> -   return err
> +   x.Vcpus = nil
> +   if numVcpus := int(xc.num_vcpus); numVcpus > 0 {


Since `numX` is now scoped to this if block, we could probably just
use `n` or similar and then drop `golenvar` from
`xenlight_golang_array_fromC`. It would remove some pretty ugly
variable names from the generated code :)

-NR

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Re: [Xen-devel] [PATCH v3 1/8] golang/xenlight: Don't try to marshall zero-length arrays in fromC

2020-01-17 Thread George Dunlap 
On 1/17/20 3:57 PM, George Dunlap wrote:
> The current fromC array code will do the "magic" casting and
> martialling even when num_foo variable is 0.  Go crashes when doing
> the cast.
> 
> Only do array marshalling if the number of elements is non-zero;
> otherwise, leave the target pointer empty (nil for Go slices, NULL for
> C arrays).
> 
> Signed-off-by: George Dunlap 
> ---
> v2:
> - Remove toC part of this, which has been folded into Nick's patch
>   series.

Er, obviously the subject line should say "v2", for the whole series. :-/

 -George

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