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Date: Wed, 05 Nov 2008 08:54:52 +0100
From: Chris Lalancette <clalance@redhat.com>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] Live migration - exec: support to be reintroduced?
References: <geqq17$om7$1@ger.gmane.org> <49113157.3090101@codemonkey.ws>
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To: qemu-devel@nongnu.org

Anthony Liguori wrote:
> Charles Duffy wrote:
>> Howdy.
>>
>> KVM's live migration support used to support an exec: protoco, 
>> allowing  either a completely arbitrary transport or a mechanism for 
>> storing system state to a separate file for later resurrection, being 
>> used in the latter by libvirt's qemu driver. I notice that this 
>> support no longer exists in the current codebase.
>> Would a patch reimplementing this support be welcome?
> 
> Absolutely.  I wasn't aware that libvirt used the exec: protocol.  I'm 
> somewhat surprised by that.  What did it use it for?

Hm, I didn't realize it used it either, but it uses it for doing a save operation:

static int qemudDomainSave(virDomainPtr dom,
                           const char *path) {
...
    if (asprintf (&command, "migrate \"exec:"
                  "dd of='%s' oflag=append conv=notrunc 2>/dev/null"
                  "\"", safe_path) == -1) {
        qemudReportError(dom->conn, dom, NULL, VIR_ERR_OPERATION_FAILED,
                         "%s", _("out of memory"));
        VIR_FREE(safe_path);
        return -1;
    }
    free(safe_path);

    if (qemudMonitorCommand(driver, vm, command, &info) < 0) {
...

I don't know if there is a better way to do that with the qemu monitor, to avoid
 using migrate altogether.  In any case, I'm sure other people would find exec:
useful as well.

-- 
Chris Lalancette