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xen-blkback: support dynamic unbind/bind

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By simply re-attaching to shared rings during connect_ring() rather than
assuming they are freshly allocated (i.e assuming the counters are zero)
it is possible for vbd instances to be unbound and re-bound from and to
(respectively) a running guest.

This has been tested by running:

while true;
  do fio --name=randwrite --ioengine=libaio --iodepth=16 \
  --rw=randwrite --bs=4k --direct=1 --size=1G --verify=crc32;
  done

in a PV guest whilst running:

while true;
  do echo vbd-$DOMID-$VBD >unbind;
  echo unbound;
  sleep 5;
  echo vbd-$DOMID-$VBD >bind;
  echo bound;
  sleep 3;
  done

in dom0 from /sys/bus/xen-backend/drivers/vbd to continuously unbind and
re-bind its system disk image.

This is a highly useful feature for a backend module as it allows it to be
unloaded and re-loaded (i.e. updated) without requiring domUs to be halted.
This was also tested by running:

while true;
  do echo vbd-$DOMID-$VBD >unbind;
  echo unbound;
  sleep 5;
  rmmod xen-blkback;
  echo unloaded;
  sleep 1;
  modprobe xen-blkback;
  echo bound;
  cd $(pwd);
  sleep 3;
  done

in dom0 whilst running the same loop as above in the (single) PV guest.

Some (less stressful) testing has also been done using a Windows HVM guest
with the latest 9.0 PV drivers installed.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Paul Durrant 2019-12-11 15:29:56 +00:00 committed by Juergen Gross
parent 1ee54195a3
commit f4eef1b652
1 changed files with 38 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

56
drivers/block/xen-blkback/xenbus.c
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@ -190,6 +190,9 @@ static int xen_blkif_map(struct xen_blkif_ring *ring, grant_ref_t *gref,
{
int err;
struct xen_blkif *blkif = ring->blkif;
const struct blkif_common_sring *sring_common;
RING_IDX rsp_prod, req_prod;
unsigned int size;
/* Already connected through? */
if (ring->irq)
@ -200,46 +203,62 @@ static int xen_blkif_map(struct xen_blkif_ring *ring, grant_ref_t *gref,
if (err < 0)
return err;
sring_common = (struct blkif_common_sring *)ring->blk_ring;
rsp_prod = READ_ONCE(sring_common->rsp_prod);
req_prod = READ_ONCE(sring_common->req_prod);
switch (blkif->blk_protocol) {
case BLKIF_PROTOCOL_NATIVE:
{
struct blkif_sring *sring;
sring = (struct blkif_sring *)ring->blk_ring;
BACK_RING_INIT(&ring->blk_rings.native, sring,
XEN_PAGE_SIZE * nr_grefs);
struct blkif_sring *sring_native =
(struct blkif_sring *)ring->blk_ring;
BACK_RING_ATTACH(&ring->blk_rings.native, sring_native,
rsp_prod, XEN_PAGE_SIZE * nr_grefs);
size = __RING_SIZE(sring_native, XEN_PAGE_SIZE * nr_grefs);
break;
}
case BLKIF_PROTOCOL_X86_32:
{
struct blkif_x86_32_sring *sring_x86_32;
sring_x86_32 = (struct blkif_x86_32_sring *)ring->blk_ring;
BACK_RING_INIT(&ring->blk_rings.x86_32, sring_x86_32,
XEN_PAGE_SIZE * nr_grefs);
struct blkif_x86_32_sring *sring_x86_32 =
(struct blkif_x86_32_sring *)ring->blk_ring;
BACK_RING_ATTACH(&ring->blk_rings.x86_32, sring_x86_32,
rsp_prod, XEN_PAGE_SIZE * nr_grefs);
size = __RING_SIZE(sring_x86_32, XEN_PAGE_SIZE * nr_grefs);
break;
}
case BLKIF_PROTOCOL_X86_64:
{
struct blkif_x86_64_sring *sring_x86_64;
sring_x86_64 = (struct blkif_x86_64_sring *)ring->blk_ring;
BACK_RING_INIT(&ring->blk_rings.x86_64, sring_x86_64,
XEN_PAGE_SIZE * nr_grefs);
struct blkif_x86_64_sring *sring_x86_64 =
(struct blkif_x86_64_sring *)ring->blk_ring;
BACK_RING_ATTACH(&ring->blk_rings.x86_64, sring_x86_64,
rsp_prod, XEN_PAGE_SIZE * nr_grefs);
size = __RING_SIZE(sring_x86_64, XEN_PAGE_SIZE * nr_grefs);
break;
}
default:
BUG();
}
err = -EIO;
if (req_prod - rsp_prod > size)
goto fail;
err = bind_interdomain_evtchn_to_irqhandler(blkif->domid, evtchn,
xen_blkif_be_int, 0,
"blkif-backend", ring);
if (err < 0) {
xenbus_unmap_ring_vfree(blkif->be->dev, ring->blk_ring);
ring->blk_rings.common.sring = NULL;
return err;
}
if (err < 0)
goto fail;
ring->irq = err;
return 0;
fail:
xenbus_unmap_ring_vfree(blkif->be->dev, ring->blk_ring);
ring->blk_rings.common.sring = NULL;
return err;
}
static int xen_blkif_disconnect(struct xen_blkif *blkif)
@ -1131,7 +1150,8 @@ static struct xenbus_driver xen_blkbk_driver = {
.ids = xen_blkbk_ids,
.probe = xen_blkbk_probe,
.remove = xen_blkbk_remove,
.otherend_changed = frontend_changed
.otherend_changed = frontend_changed,
.allow_rebind = true,
};
int xen_blkif_xenbus_init(void)