Re: [Xen-devel] [PATCH v2 08/22] golang/xenlight: define MsVmGenid builtin type

From: George Dunlap <george.dunlap@citrix.com>
To: Nick Rosbrook <rosbrookn@gmail.com>, <xen-devel@lists.xenproject.org>
Cc: Nick Rosbrook <rosbrookn@ainfosec.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	kerriganb@ainfosec.com, Wei Liu <wl@xen.org>
Subject: Re: [Xen-devel] [PATCH v2 08/22] golang/xenlight: define MsVmGenid builtin type
Date: Wed, 4 Dec 2019 17:00:09 +0000	[thread overview]
Message-ID: <45d555e3-0879-ad47-f24e-7d3c6ea1322d@citrix.com> (raw)
In-Reply-To: <25ebb96e473b1405d202f4334725fd68cb882c38.1573840474.git.rosbrookn@ainfosec.com>

On 11/15/19 7:44 PM, Nick Rosbrook wrote:
> From: Nick Rosbrook <rosbrookn@ainfosec.com>
> 
> Define MsVmGenid as [int(C.LIBXL_MS_VM_GENID_LEN)]byte and implement fromC and toC functions.
> 
> Signed-off-by: Nick Rosbrook <rosbrookn@ainfosec.com>
> Reviewed-by: George Dunlap <george.dunlap@citrix.com>
> ---
>  tools/golang/xenlight/xenlight.go | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/tools/golang/xenlight/xenlight.go b/tools/golang/xenlight/xenlight.go
> index eb0d309543..108b50124a 100644
> --- a/tools/golang/xenlight/xenlight.go
> +++ b/tools/golang/xenlight/xenlight.go
> @@ -216,6 +216,29 @@ func (mac Mac) toC() (C.libxl_mac, error) {
>  	return cmac, nil
>  }
>  
> +// MsVmGenid represents a libxl_ms_vm_genid.
> +type MsVmGenid [int(C.LIBXL_MS_VM_GENID_LEN)]byte
> +
> +func (mvg *MsVmGenid) fromC(cmvg *C.libxl_ms_vm_genid) error {
> +	b := (*[int(C.LIBXL_MS_VM_GENID_LEN)]C.uint8_t)(unsafe.Pointer(&cmvg.bytes[0]))
> +
> +	for i, v := range b {
> +		mvg[i] = byte(v)
> +	}

Sorry to come back to this -- is there a reason we can't just do
something like this?

func (u *Uuid) fromC(c *C.libxl_uuid) error {
	for i := range *u {
		u[i] = byte(c.uuid[i])
	}

	return nil
}

I.e., the only reason we seem to be doing the cast is to have an
appropriate type to range over; but we can just range over `*u` instead.

 -George

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