Re: vhost-user technical isssues

[Linhaifeng <haifeng.lin-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>]

On 2014/11/12 5:37, Xie, Huawei wrote:
> Hi Tetsuya:
> There are two major technical issues in my mind for vhost-user implementation.
> 
> 1) memory region map
> Vhost-user passes us file fd and offset for each memory region. Unfortunately the mmap offset is "very" wrong. I discovered this issue long time ago, and also found
> that I couldn't mmap the huge page file even with correct offset(need double check).
> Just now I find that people reported this issue on Nov 3.
> [Qemu-devel] [PULL 27/29] vhost-user: fix mmap offset calculation
> Anyway, I turned to the same idea used in our DPDK vhost-cuse: only use the fd for region(0) to map the  whole file.
> I think we should use this way temporarily to support qemu-2.1 as it has that bug.
> 

the size of region 0 is not same as the file size. may be you should mmap the other region.

region 0:
        gpa = 0x0
        size = 655360
        ua = 0x2aaaaac00000
        offset = 0

region 1:// use this region to mmap.BTW how to avoid mmap twice when there are two devices?
        gpa = 0xC0000
        size = 2146697216
        ua = 0x2aaaaacc0000
        offset = 786432



> 2) what message is the indicator for vhost start/release?
> Previously  for vhost-cuse, it has SET_BACKEND message.
> What we should do for vhost-user?
> SET_VRING_KICK for start?
> What about for release?
> Unlike the kernel virtio, the DPDK virtio in guest could be restarted. 
> 
> Thoughts?
> 
> -huawei
> 
> 

-- 
Regards,
Haifeng