Re: [Xen-devel] [PATCH v2] golang/xenlight: Add libxl_utils support

[George Dunlap <George.Dunlap@xxxxxxxxxx>]

> On Jun 28, 2019, at 5:32 PM, George Dunlap <george.dunlap@xxxxxxxxxx> wrote:
> 
> On 6/28/19 9:25 AM, Nicolas Belouin wrote:
>> The Go bindings for libxl miss functions from libxl_utils, let's start
>> with the simple libxl_domid_to_name and its counterpart
>> libxl_name_to_domid.
>> 
>> Signed-off-by: Nicolas Belouin <nicolas.belouin@xxxxxxxxx>
> 
> Just for future reference, below your SoB, it's good practice to put a
> `---` line (below which everything will be ignored), and a list of the
> changes you made.  E.g,:
> 
> Signed-off-by: Nicolas Belouin <nicolas.belouin@xxxxxxxxx>
> ---
> v2:
> - Don't leak C string returned by libxl_domid_to_name
> 
> One more thing...
> 
>> +//char* libxl_domid_to_name(libxl_ctx *ctx, uint32_t domid);
>> +func (Ctx *Context) DomidToName(id Domid) (name string) {
>> +    cDomName := C.libxl_domid_to_name(Ctx.ctx, C.uint32_t(id))
>> +    defer C.free(unsafe.Pointer(cDomName))
>> +
>> +    name = C.GoString(cDomName)
> 
> libxl_domid_to_name() returns NULL if domid doesn't exist.  Will this
> code DTRT (returning 'nil' in that case)?  Or will it crash / do
> something else?
> 
> I couldn't actually find the answer in a quick search for the
> documentation.  Any chance you could build a test program to see what
> happens?
> 
> Alternately, we could play it safe and always check cDomName for `nil`
> before passing it to C.GoString().

I just asked, and it turns out if C.GoString() is passed a nil pointer, it 
returns the empty string (“”), which is what we want.  It’s not documented yet, 
but there’s a ticket to document it soon.

https://github.com/golang/go/issues/32734

So this is ready to go in:

Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>

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