Re: hotplug issue of vhost-user-blk

[Li Feng]

Thanks!
After waiting some seconds after device_del:
(qemu) device_del spdk_vhost_blk2
sleep 5
(qemu) chardev-remove spdk_vhost_blk2
Error: Chardev 'spdk_vhost_blk2' is busy

It works. However, I find some crashes about the vhost-user-blk.
I will send out the patches after all tests.

Thanks,

Feng Li

Igor Mammedov <address@hidden> 于2020年4月8日周三 下午6:40写道：
>
> On Wed, 8 Apr 2020 10:25:42 +0800
> Li Feng <address@hidden> wrote:
>
> > Hi all,
> >
> > Hotplug of vhost-user-blk doesn't not work in qemu master branch and
> > all previous version.
> >
> > The action I insert a vhost-user-blk disk is:
> > (qemu) chardev-add socket,id=spdk_vhost_blk2,path=/vhost-blk.0,reconnect=1
> > (qemu) device_add
> > vhost-user-blk-pci,chardev=spdk_vhost_blk2,id=spdk_vhost_blk2,num-queues=4
> >
> > Until here, it's well.
> >
> > Then I unplug it from qemu:
> > (qemu) device_del spdk_vhost_blk2
> > (qemu) chardev-remove spdk_vhost_blk2
> > Error: Chardev 'spdk_vhost_blk2' is busy
> >
> > The related code is here:
> > qmp_chardev_remove
> >     -> qemu_chr_is_busy
> >     -> object_unparent(OBJECT(chr));
> >
> >  330 static bool qemu_chr_is_busy(Chardev *s)
> >  331 {
> >  332     if (CHARDEV_IS_MUX(s)) {
> >  333         MuxChardev *d = MUX_CHARDEV(s);
> >  334         return d->mux_cnt >= 0;
> >  335     } else {
> >  336         return s->be != NULL;
> >  337     }
> >  338 }
> >
> > My question is:
> > 1. s->be is set to NULL when qemu_chr_fe_deinit is called.
> > However, the qmp_chardev_remove is blocked at qemu_chr_is_busy check,
> > then the object_unparent will not be called.
> > 2. Is there a path that device_del will trigger the s->be that been set to 
> > NULL?
>
> device_del is request for guest to eject device and once it's done backend
> could be removed.
>
> what's you command line? (so I could point out entry point where ejection 
> happens
> for you to troubleshoot it further)
>
> >
> > How should I fix this issue?
> > I have tested that comment the qemu_chr_is_busy works well.
> >
> > Thanks in advance.
> >
> > Feng Li
> >
>

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