Messages in this thread | | | Date | Tue, 17 Nov 2020 18:38:11 +0100 | From | Stefano Garzarella <> | Subject | Re: [PATCH RFC 04/12] vdpa: add vdpa simulator for block device |
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On Tue, Nov 17, 2020 at 04:43:42PM +0000, Stefan Hajnoczi wrote: >On Tue, Nov 17, 2020 at 03:16:20PM +0100, Stefano Garzarella wrote: >> On Tue, Nov 17, 2020 at 11:11:21AM +0000, Stefan Hajnoczi wrote: >> > On Fri, Nov 13, 2020 at 02:47:04PM +0100, Stefano Garzarella wrote: >> > > +static void vdpasim_blk_work(struct work_struct *work) >> > > +{ >> > > + struct vdpasim *vdpasim = container_of(work, struct vdpasim, work); >> > > + u8 status = VIRTIO_BLK_S_OK; >> > > + int i; >> > > + >> > > + spin_lock(&vdpasim->lock); >> > > + >> > > + if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK)) >> > > + goto out; >> > > + >> > > + for (i = 0; i < VDPASIM_BLK_VQ_NUM; i++) { >> > > + struct vdpasim_virtqueue *vq = &vdpasim->vqs[i]; >> > > + >> > > + if (!vq->ready) >> > > + continue; >> > > + >> > > + while (vringh_getdesc_iotlb(&vq->vring, &vq->iov, &vq->iov, >> > > + &vq->head, GFP_ATOMIC) > 0) { >> > > + >> > > + int write; >> > > + >> > > + vq->iov.i = vq->iov.used - 1; >> > > + write = vringh_iov_push_iotlb(&vq->vring, &vq->iov, &status, 1); >> > > + if (write <= 0) >> > > + break; >> > >> > We're lucky the guest driver doesn't crash after VIRTIO_BLK_T_GET_ID? :) >> >> The crash could happen if the simulator doesn't put the string terminator, >> but in virtio_blk.c, the serial_show() initialize the buffer putting the >> string terminator in the VIRTIO_BLK_ID_BYTES element: >> >> buf[VIRTIO_BLK_ID_BYTES] = '\0'; >> err = virtblk_get_id(disk, buf); >> >> This should prevent the issue, right? >> >> However in the last patch of this series I implemented VIRTIO_BLK_T_GET_ID >> support :-) > >Windows, BSD, macOS, etc guest drivers aren't necessarily going to >terminate or initialize the serial string buffer.
Unfortunately I discovered that VIRTIO_BLK_T_GET_ID is not in the VIRTIO specs, so, just for curiosity, I checked the QEMU code and I found this:
case VIRTIO_BLK_T_GET_ID: { /* * NB: per existing s/n string convention the string is * terminated by '\0' only when shorter than buffer. */ const char *serial = s->conf.serial ? s->conf.serial : ""; size_t size = MIN(strlen(serial) + 1, MIN(iov_size(in_iov, in_num), VIRTIO_BLK_ID_BYTES)); iov_from_buf(in_iov, in_num, 0, serial, size); virtio_blk_req_complete(req, VIRTIO_BLK_S_OK); virtio_blk_free_request(req); break; }
It seems that the device emulation in QEMU expects that the driver terminates the serial string buffer.
Do you know why VIRTIO_BLK_T_GET_ID is not in the specs? Should we add it?
Thanks, Stefano
> >Anyway, the later patch that implements VIRTIO_BLK_T_GET_ID solves this >issue! Thanks.
> >Stefan
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