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Date: Tue, 10 Feb 2015 13:04:22 +0100
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v1 1/2] vhost-user: support SET_MEM_TABLE
 waite the result of mmap
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To: Linhaifeng <haifeng.lin@huawei.com>
Cc: arei.gonglei@huawei.com, qemu-devel@nongnu.org

On Tue, Feb 10, 2015 at 07:59:16PM +0800, Linhaifeng wrote:
> 
> 
> On 2015/2/10 18:41, Michael S. Tsirkin wrote:
> > On Tue, Feb 10, 2015 at 06:27:04PM +0800, Linhaifeng wrote:
> >>
> >>
> >> On 2015/2/10 16:46, Michael S. Tsirkin wrote:
> >>> On Tue, Feb 10, 2015 at 01:48:12PM +0800, linhaifeng wrote:
> >>>> From: Linhaifeng <haifeng.lin@huawei.com>
> >>>>
> >>>> Slave should reply to master and set u64 to 0 if
> >>>> mmap all regions success otherwise set u64 to 1.
> >>>>
> >>>> Signed-off-by: Linhaifeng <haifeng.lin@huawei.com>
> >>>
> >>> How does this work with existig slaves though?
> >>>
> >>
> >> Slaves should work like this:
> >>
> >> int set_mem_table(...)
> >> {
> >>     ....
> >>     for (idx = 0, i = 0; idx < memory.nregions; idx++) {
> >> 	....
> >>     	mem = mmap(..);
> >> 	if (MAP_FAILED == mem) {
> >> 		msg->msg.u64 = 1;
> >>                 msg->msg.size = MEMB_SIZE(VhostUserMsg, u64);
> >> 		return 1;
> >> 	}
> >>     }
> >>
> >>     ....
> >>
> >>     msg->msg.u64 = 0;
> >>     msg->msg.size = MEMB_SIZE(VhostUserMsg, u64);
> >>     return 1;
> >> }
> >>
> >> If slaves not reply QEMU will always wait.
> > 
> > Are you sure existing slaves reply?
> 
> No.May be the existing slaves need add reply in their codes.

So that's not good. We need a way to negotiate the capability,
we can't just deadlock with legacy slaves.

> > 
> >>>> ---
> >>>>  docs/specs/vhost-user.txt | 1 +
> >>>>  1 file changed, 1 insertion(+)
> >>>>
> >>>> diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt
> >>>> index 650bb18..c96bf6b 100644
> >>>> --- a/docs/specs/vhost-user.txt
> >>>> +++ b/docs/specs/vhost-user.txt
> >>>> @@ -171,6 +171,7 @@ Message types
> >>>>        Id: 5
> >>>>        Equivalent ioctl: VHOST_SET_MEM_TABLE
> >>>>        Master payload: memory regions description
> >>>> +      Slave payload: u64 (0:success >0:failed)
> >>>>  
> >>>>        Sets the memory map regions on the slave so it can translate the vring
> >>>>        addresses. In the ancillary data there is an array of file descriptors
> >>>> -- 
> >>>> 1.7.12.4
> >>>>
> >>>
> >>>
> >>
> >> -- 
> >> Regards,
> >> Haifeng
> > 
> > .
> > 
> 
> -- 
> Regards,
> Haifeng