On Fri, Jan 31, 2020 at 05:22:47PM +0100, Paolo Bonzini wrote: > I have just found this email... sorry for the delay. > > On 10/01/20 07:10, Yang Zhong wrote: > >> No. If virtio-blk works, the bug is in vhost-user-blk; if virtio-blk needs > >> no check in cpu count, vhost-user-blk also doesn't. > >> > >> You need to check first if the bug is in QEMU or the vhost-user-blk server. > > > > (1). Seabios issue > > In init_virtio_blk() function, which set VIRTIO_CONFIG_S_DRIVER_OK > > status to qemu vhost-user-blk device. > > > > // the related code > > ...... > > status |= VIRTIO_CONFIG_S_DRIVER_OK; > > vp_set_status(&vdrive->vp, status); > > ...... > > > > I think there is no need for seabios to set VIRTIO_CONFIG_S_DRIVER_OK > > status to qemu vhost-user-blk device. > > It does so because it cannot know how it will be used. It could be used > by the guest boot loader to load a kernel, for example. SeaBIOS sets > DRIVER_OK because it has loaded a driver for the disk; that's exactly > what DRIVER_OK signals.
Right. More specifically DRIVER_OK means driver finished setup and is going to add buffers and process used ones, so device should start looking at queues. > > > In fact, this time vhost_user_blk_start almost do nothing because > > the real guest virtio-blk driver still not started yet. This time, > > there is only one vq can be used(this vq should be inited in seabios). > > > > When the guest virtio-blk driver really start and complet the > > probe(), the guest virtio-blk driver will set > > VIRTIO_CONFIG_S_DRIVER_OK to vhost-user-blk device again. This > > time, this driver will allocate RIGHT queue num according to > > MIN(vcpu, num_vqs). > > Doesn't it first reset the status to 0? > > > (2). DPDK issue > > DPDK does not know the real queue number used by guest virtio-blk > > driver and it only know the queue number from vhost-user-blk > > commond line. Once the guest virtio-blk driver change the queue > > number according to MIN(vcpu, num_vqs), DPDK still use previous > > queue number and it think virtio is never ready by > > virtio_is_ready() function. > > What is virtio_is_ready()? The virtio device should not wait for all > the queues to be set. A device is ready when it sets DRIVER_OK, and > that's it. Or - if we want to support legacy guests, and due to a bunch of legacy guest bugs - if a legacy guest kicked a queue before setting DRIVER_OK. > > or DPDK can get the real queue number by checking if the vring.desc > > is NON-NULL. > > Note that there is no requirement that the driver initializes a > consecutive number of virtqueues. It is acceptable for it to initialize > virtqueues 0, 1 and 57. It seems like the bug is in DPDK, possibly more > than one... > > Paolo > > > By the way, vhost SCSI device has the same issue with > > vhost-user-blk device. > > > > Yang > > > >> Paolo > >
