Re: [Xen-devel] [PATCH 1/9] golang/xenlight: Don't try to marshall zero-length arrays

[George Dunlap <george.dunlap@citrix.com>]

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On 12/27/19 4:32 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.
> 
> Furthermore, the current toC array code will convert a nil slice into
> a zero-length malloc.  The resulting pointer is non-NULL, and confuses
> libxl.
> 
> 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).
> 
> The toC half of this should be folded into "golang/xenlight:
> implement array Go to C marshaling".
> 
> Signed-off-by: George Dunlap <george.dunlap@citrix.com>

The .go program I used to test this series is attached, to give you an
idea what the current iteration looks like, and potentially give it a spin.

 -George

[-- Attachment #2: xltest.go --]
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package main

import (
	"fmt"
	xl "golang.xenproject.org/xenlight"
)

func main() {
	ctx, err := xl.NewContext()
	if err != nil {
		fmt.Printf("Opening context: %v\n", err)
		return
	}
	defer ctx.Close()

	doms := ctx.ListDomain()
	for i := range doms {
		fmt.Printf("%d %v\n", doms[i].Domid, doms[i].Uuid)
	}

	fmt.Printf("String for error ErrorNonspecific: %v\n", xl.ErrorNonspecific)

	// type = "pv"
	dconf, err := xl.NewDomainConfig(xl.DomainTypePv)
	if err != nil {
		fmt.Printf("NewDomainConfig: %v\n", err)
		return
	}
	dconf.CInfo.Type = xl.DomainTypePv
	// name = "c6-01"
	dconf.CInfo.Name = "c6-01"
	// vcpus=4
	dconf.BInfo.MaxVcpus = 4
	// memory = "2048"
	dconf.BInfo.MaxMemkb = 2048 * 1024
	dconf.BInfo.TargetMemkb = 2048 * 1024
	// on_crash = 'destroy'
	dconf.OnCrash = xl.ActionOnShutdownDestroy
	// bootloader = "pygrub"
	dconf.BInfo.Bootloader = "pygrub"
	// disk = [ 'vdev=hda,format=raw,target=/images/c6-01.raw']
	{
		disk, err := xl.NewDeviceDisk()
		if err != nil {
			fmt.Printf("NewDeviceDisk: %v\n", err)
			return
		}
		disk.Vdev = "hda"
		//disk.DiskBackend = xl.DiskBackendPhy
		disk.Format = xl.DiskFormatRaw
		disk.PdevPath = "/images/c6-01.raw"
		dconf.Disks = append(dconf.Disks, *disk)
	}
	// vif = [ 'mac=5a:5b:d6:f1:d6:b4' ]
	{
		vif, err := xl.NewDeviceNic()
		if err != nil {
			fmt.Printf("NewDeviceNic: %v\n", err)
			return
		}
		vif.Mac = xl.Mac{ 0x5a, 0x5b, 0xd6, 0x31, 0xd6, 0xb4 }
		dconf.Nics = append(dconf.Nics, *vif)
	}
	// serial='pty' # HVM only

	did, err := ctx.DomainCreateNew(dconf)

	if err != nil {
		fmt.Printf("Creating domain: %v\n", err)
		return
	}

	fmt.Printf("Domain %s(%d) created successfully", dconf.CInfo.Name, did)
}

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