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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Fri, 17 Jul 2015 14:57:26 +0200
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Subject: Re: [Qemu-devel] [PATCH v4 1/1] vhost user: add support of live
	migration
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Cc: Linhaifeng <haifeng.lin@huawei.com>, "Michael S. Tsirkin" <mst@redhat.com>, Thibaut Collet <thibaut.collet@6wind.com>, jasowang@redhat.com, QEMU <qemu-devel@nongnu.org>, stefanha@redhat.com



On 17/07/2015 12:34, Marc-André Lureau wrote:
> On Fri, Jul 17, 2015 at 4:25 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> > But LOG_BASE makes little sense across processes, and LOG_FD is unused
> > in QEMU, isn't it?  So this patch is not enough to add support of live
> > migration.
>
> You are right, LOG_BASE doesn't make much sense, and LOG_FD isn't
> used, despite some code already there. Furthermore, the log is
> allocated with regular malloc, hardly shareable.

LOG_FD is implemented in the kernel drivers/vhost/vhost.c.  It seems to
be an eventfd-like mechanism to save on dirty bitmap scans.  However,
it's not well documented how to implement it in a correct way.

In any case, live migration needs a new message type (like LOG_MMAP_FD)
in the vhost-user protocol.

Paolo