On Fri, Jan 13, 2012 at 04:48:30PM -0500, Dave Allan wrote:
> On Fri, Jan 13, 2012 at 02:51:23PM -0600, Adam Litke wrote:
> > Qemu has changed the semantics of the "block_job_cancel" API. Originally, the
> > operation was synchronous (ie. upon command completion, the operation was
> > guaranteed to be completely stopped). With the new semantics, a
> > "block_job_cancel" merely requests that the operation be cancelled and an event
> > is triggered once the cancellation request has been honored.
> >
> > To adopt the new semantics while preserving compatibility I propose the
> > following updates to the virDomainBlockJob API:
> >
> > A new block job event type VIR_DOMAIN_BLOCK_JOB_CANCELLED will be recognized by
> > libvirt. Regardless of the flags used with virDomainBlockJobAbort, this event
> > will be raised whenever it is received from qemu. This event indicates that a
> > block job has been successfully cancelled.
> >
> > A new extension flag VIR_DOMAIN_BLOCK_JOB_ABORT_ASYNC will be added to the
> > virDomainBlockJobAbort API. When enabled, this function will operate
> > asynchronously (ie, it can return before the job has actually been cancelled).
> > When the API is used in this mode, it is the responsibility of the caller to
> > wait for a VIR_DOMAIN_BLOCK_JOB_CANCELLED event or poll via the
> > virDomainGetBlockJobInfo API to check the cancellation status.
> >
> > Without the VIR_DOMAIN_BLOCK_JOB_ABORT_ASYNC flag, libvirt will internally poll
> > using qemu's "query-block-jobs" API and will not return until the operation has
> > been completed. API users are advised that this operation is unbounded and
> > further interaction with the domain during this period may block.
> >
> > This patch implements the new event type, the API flag, and the polling. The
> > main outstanding issue is whether we should bound the amount of time we will
> > wait for cancellation and return an error.
> >
> > Comments on this proposal?
>
> Hi Adam,
>
> Thanks for the patch. That approach seems reasonable. Re: bounding
> the amount of time we wait for cancellation, if the time isn't
> bounded, what happens if the cancellation never happens? IMO the most
> important thing is to make sure that the caller has a way to return to
> a normally functioning state even if the virDomainBlockJobAbort call
> is unable to cancel the job.
Yes, agreed. But this brings up the familiar problem with timeouts: selecting
the right amount of time to wait. I don't have a good answer here, but it's not
really all that bad if we bail out too early. In that case we can just return
VIR_ERR_OPERATION_TIMEOUT to the caller and they can retry the operation again.
Unfortunately, these semantics were not present in the initial API. Is adding a
new error condition (timeout) to an existing API allowed?
>
> I'll defer to the other folks on the code, since I am at this point
> likely to do more harm than good. :)
>
> Dave
>
>
> > Signed-off-by: Adam Litke <agl@xxxxxxxxxx>
> > Cc: Stefan Hajnoczi <stefanha@xxxxxxxxx>
> > Cc: Eric Blake <eblake@xxxxxxxxxx>
> > ---
> > include/libvirt/libvirt.h.in | 10 ++++++++++
> > src/libvirt.c | 9 ++++++++-
> > src/qemu/qemu_driver.c | 24 +++++++++++++++++-------
> > src/qemu/qemu_monitor.c | 24 ++++++++++++++++++++++++
> > src/qemu/qemu_monitor.h | 2 ++
> > src/qemu/qemu_monitor_json.c | 36 +++++++++++++++++++++++++++++-------
> > 6 files changed, 90 insertions(+), 15 deletions(-)
> >
> > diff --git a/include/libvirt/libvirt.h.in b/include/libvirt/libvirt.h.in
> > index e436f3c..fc7f028 100644
> > --- a/include/libvirt/libvirt.h.in
> > +++ b/include/libvirt/libvirt.h.in
> > @@ -1776,6 +1776,15 @@ typedef enum {
> > VIR_DOMAIN_BLOCK_JOB_TYPE_PULL = 1,
> > } virDomainBlockJobType;
> >
> > +/**
> > + * virDomainBlockJobAbortFlags:
> > + *
> > + * VIR_DOMAIN_BLOCK_JOB_ABORT_ASYNC: Request only, do not wait for completion
> > + */
> > +typedef enum {
> > + VIR_DOMAIN_BLOCK_JOB_ABORT_ASYNC = 1,
> > +} virDomainBlockJobAbortFlags;
> > +
> > /* An iterator for monitoring block job operations */
> > typedef unsigned long long virDomainBlockJobCursor;
> >
> > @@ -3293,6 +3302,7 @@ typedef void (*virConnectDomainEventGraphicsCallback)(virConnectPtr conn,
> > typedef enum {
> > VIR_DOMAIN_BLOCK_JOB_COMPLETED = 0,
> > VIR_DOMAIN_BLOCK_JOB_FAILED = 1,
> > + VIR_DOMAIN_BLOCK_JOB_CANCELLED = 2,
> > } virConnectDomainEventBlockJobStatus;
> >
> > /**
> > diff --git a/src/libvirt.c b/src/libvirt.c
> > index a540424..0e886f5 100644
> > --- a/src/libvirt.c
> > +++ b/src/libvirt.c
> > @@ -17299,7 +17299,7 @@ error:
> > * virDomainBlockJobAbort:
> > * @dom: pointer to domain object
> > * @disk: path to the block device, or device shorthand
> > - * @flags: extra flags; not used yet, so callers should always pass 0
> > + * @flags: bitwise or of virDomainBlockJobAbortFlags
> > *
> > * Cancel the active block job on the given disk.
> > *
> > @@ -17310,6 +17310,13 @@ error:
> > * can be found by calling virDomainGetXMLDesc() and inspecting
> > * elements within //domain/devices/disk.
> > *
> > + * By default, this function performs a synchronous operation and the caller
> > + * may assume that the operation has completed when 0 is returned. However,
> > + * BlockJob operations may take a long time to complete, and during this time
> > + * further domain interactions may be unresponsive. To avoid this problem, pass
> > + * VIR_DOMAIN_BLOCK_JOB_ABORT_ASYNC in the flags argument to enable asynchronous
> > + * behavior. When the job has been cancelled, a BlockJob event will be emitted.
> > + *
> > * Returns -1 in case of failure, 0 when successful.
> > */
> > int virDomainBlockJobAbort(virDomainPtr dom, const char *disk,
> > diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> > index 712f1fc..d971a5f 100644
> > --- a/src/qemu/qemu_driver.c
> > +++ b/src/qemu/qemu_driver.c
> > @@ -11379,7 +11379,7 @@ cleanup:
> > static int
> > qemuDomainBlockJobImpl(virDomainPtr dom, const char *path,
> > unsigned long bandwidth, virDomainBlockJobInfoPtr info,
> > - int mode)
> > + int flags, int mode)
> > {
> > struct qemud_driver *driver = dom->conn->privateData;
> > virDomainObjPtr vm = NULL;
> > @@ -11420,6 +11420,15 @@ qemuDomainBlockJobImpl(virDomainPtr dom, const char *path,
> > qemuDomainObjEnterMonitorWithDriver(driver, vm);
> > priv = vm->privateData;
> > ret = qemuMonitorBlockJob(priv->mon, device, bandwidth, info, mode);
> > + /*
> > + * Qemu provides asynchronous block job cancellation but without the
> > + * VIR_DOMAIN_BLOCK_JOB_ABORT_ASYNC flag libvirt guarantees a synchronous
> > + * operation. Provide this behavior by waiting here (with the monitor
> > + * locked) so we don't get confused by newly scheduled block jobs.
> > + */
> > + if (ret == 0 && mode == BLOCK_JOB_ABORT &&
> > + !(flags & VIR_DOMAIN_BLOCK_JOB_ABORT_ASYNC))
> > + ret = qemuMonitorBlockJobCancelWait(priv->mon, device);
> > qemuDomainObjExitMonitorWithDriver(driver, vm);
> >
> > endjob:
> > @@ -11439,8 +11448,7 @@ cleanup:
> > static int
> > qemuDomainBlockJobAbort(virDomainPtr dom, const char *path, unsigned int flags)
> > {
> > - virCheckFlags(0, -1);
> > - return qemuDomainBlockJobImpl(dom, path, 0, NULL, BLOCK_JOB_ABORT);
> > + return qemuDomainBlockJobImpl(dom, path, 0, NULL, flags, BLOCK_JOB_ABORT);
> > }
> >
> > static int
> > @@ -11448,7 +11456,7 @@ qemuDomainGetBlockJobInfo(virDomainPtr dom, const char *path,
> > virDomainBlockJobInfoPtr info, unsigned int flags)
> > {
> > virCheckFlags(0, -1);
> > - return qemuDomainBlockJobImpl(dom, path, 0, info, BLOCK_JOB_INFO);
> > + return qemuDomainBlockJobImpl(dom, path, 0, info, flags, BLOCK_JOB_INFO);
> > }
> >
> > static int
> > @@ -11456,7 +11464,8 @@ qemuDomainBlockJobSetSpeed(virDomainPtr dom, const char *path,
> > unsigned long bandwidth, unsigned int flags)
> > {
> > virCheckFlags(0, -1);
> > - return qemuDomainBlockJobImpl(dom, path, bandwidth, NULL, BLOCK_JOB_SPEED);
> > + return qemuDomainBlockJobImpl(dom, path, bandwidth, NULL, flags,
> > + BLOCK_JOB_SPEED);
> > }
> >
> > static int
> > @@ -11466,9 +11475,10 @@ qemuDomainBlockPull(virDomainPtr dom, const char *path, unsigned long bandwidth,
> > int ret;
> >
> > virCheckFlags(0, -1);
> > - ret = qemuDomainBlockJobImpl(dom, path, bandwidth, NULL, BLOCK_JOB_PULL);
> > + ret = qemuDomainBlockJobImpl(dom, path, bandwidth, NULL, flags,
> > + BLOCK_JOB_PULL);
> > if (ret == 0 && bandwidth != 0)
> > - ret = qemuDomainBlockJobImpl(dom, path, bandwidth, NULL,
> > + ret = qemuDomainBlockJobImpl(dom, path, bandwidth, NULL, flags,
> > BLOCK_JOB_SPEED);
> > return ret;
> > }
> > diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
> > index ad7e2a5..5c22486 100644
> > --- a/src/qemu/qemu_monitor.c
> > +++ b/src/qemu/qemu_monitor.c
> > @@ -2585,6 +2585,30 @@ int qemuMonitorScreendump(qemuMonitorPtr mon,
> > return ret;
> > }
> >
> > +/* Poll the monitor to wait for the block job on a given disk to end.
> > + * We don't need to worry about another block job starting since we have the
> > + * driver locked. */
> > +int
> > +qemuMonitorBlockJobCancelWait(qemuMonitorPtr mon, const char *device)
> > +{
> > + VIR_DEBUG("mon=%p, device=%p", mon, device);
> > + /* XXX: Should we provide some sort of escape hatch for this wait? */
> > + while (1) {
> > + /* Poll every 100ms */
> > + int ret;
> > + struct timespec ts = { .tv_sec = 0, .tv_nsec = 100 * 1000 * 1000ull };
> > + virDomainBlockJobInfo info;
> > +
> > + ret = qemuMonitorBlockJob(mon, device, 0, &info, BLOCK_JOB_INFO);
> > + if (ret < 0)
> > + return -1;
> > + else if (ret == 0)
> > + return 0;
> > + else
> > + nanosleep(&ts, NULL);
> > + }
> > +}
> > +
> > int qemuMonitorBlockJob(qemuMonitorPtr mon,
> > const char *device,
> > unsigned long bandwidth,
> > diff --git a/src/qemu/qemu_monitor.h b/src/qemu/qemu_monitor.h
> > index 15acf8b..afc081e 100644
> > --- a/src/qemu/qemu_monitor.h
> > +++ b/src/qemu/qemu_monitor.h
> > @@ -510,6 +510,8 @@ typedef enum {
> > BLOCK_JOB_PULL = 3,
> > } BLOCK_JOB_CMD;
> >
> > +int qemuMonitorBlockJobCancelWait(qemuMonitorPtr mon, const char *device);
> > +
> > int qemuMonitorBlockJob(qemuMonitorPtr mon,
> > const char *device,
> > unsigned long bandwidth,
> > diff --git a/src/qemu/qemu_monitor_json.c b/src/qemu/qemu_monitor_json.c
> > index 7eb2a92..2ca8eeb 100644
> > --- a/src/qemu/qemu_monitor_json.c
> > +++ b/src/qemu/qemu_monitor_json.c
> > @@ -57,7 +57,8 @@ static void qemuMonitorJSONHandleIOError(qemuMonitorPtr mon, virJSONValuePtr dat
> > static void qemuMonitorJSONHandleVNCConnect(qemuMonitorPtr mon, virJSONValuePtr data);
> > static void qemuMonitorJSONHandleVNCInitialize(qemuMonitorPtr mon, virJSONValuePtr data);
> > static void qemuMonitorJSONHandleVNCDisconnect(qemuMonitorPtr mon, virJSONValuePtr data);
> > -static void qemuMonitorJSONHandleBlockJob(qemuMonitorPtr mon, virJSONValuePtr data);
> > +static void qemuMonitorJSONHandleBlockJobCompleted(qemuMonitorPtr mon, virJSONValuePtr data);
> > +static void qemuMonitorJSONHandleBlockJobCancelled(qemuMonitorPtr mon, virJSONValuePtr data);
> >
> > struct {
> > const char *type;
> > @@ -73,7 +74,8 @@ struct {
> > { "VNC_CONNECTED", qemuMonitorJSONHandleVNCConnect, },
> > { "VNC_INITIALIZED", qemuMonitorJSONHandleVNCInitialize, },
> > { "VNC_DISCONNECTED", qemuMonitorJSONHandleVNCDisconnect, },
> > - { "BLOCK_JOB_COMPLETED", qemuMonitorJSONHandleBlockJob, },
> > + { "BLOCK_JOB_COMPLETED", qemuMonitorJSONHandleBlockJobCompleted, },
> > + { "BLOCK_JOB_CANCELLED", qemuMonitorJSONHandleBlockJobCancelled, },
> > };
> >
> >
> > @@ -685,13 +687,14 @@ static void qemuMonitorJSONHandleVNCDisconnect(qemuMonitorPtr mon, virJSONValueP
> > qemuMonitorJSONHandleVNC(mon, data, VIR_DOMAIN_EVENT_GRAPHICS_DISCONNECT);
> > }
> >
> > -static void qemuMonitorJSONHandleBlockJob(qemuMonitorPtr mon, virJSONValuePtr data)
> > +static void qemuMonitorJSONHandleBlockJobImpl(qemuMonitorPtr mon,
> > + virJSONValuePtr data,
> > + int event)
> > {
> > const char *device;
> > const char *type_str;
> > int type = VIR_DOMAIN_BLOCK_JOB_TYPE_UNKNOWN;
> > unsigned long long offset, len;
> > - int status = VIR_DOMAIN_BLOCK_JOB_FAILED;
> >
> > if ((device = virJSONValueObjectGetString(data, "device")) == NULL) {
> > VIR_WARN("missing device in block job event");
> > @@ -716,13 +719,32 @@ static void qemuMonitorJSONHandleBlockJob(qemuMonitorPtr mon, virJSONValuePtr da
> > if (STREQ(type_str, "stream"))
> > type = VIR_DOMAIN_BLOCK_JOB_TYPE_PULL;
> >
> > - if (offset != 0 && offset == len)
> > - status = VIR_DOMAIN_BLOCK_JOB_COMPLETED;
> > + switch (event) {
> > + case VIR_DOMAIN_BLOCK_JOB_COMPLETED:
> > + /* Make sure the whole device has been processed */
> > + if (offset != len)
> > + event = VIR_DOMAIN_BLOCK_JOB_FAILED;
> > + break;
> > + case VIR_DOMAIN_BLOCK_JOB_FAILED:
> > + case VIR_DOMAIN_BLOCK_JOB_CANCELLED:
> > + break;
> > + }
> >
> > out:
> > - qemuMonitorEmitBlockJob(mon, device, type, status);
> > + qemuMonitorEmitBlockJob(mon, device, type, event);
> > +}
> > +
> > +static void qemuMonitorJSONHandleBlockJobCompleted(qemuMonitorPtr mon,
> > + virJSONValuePtr data)
> > +{
> > + qemuMonitorJSONHandleBlockJobImpl(mon, data, VIR_DOMAIN_BLOCK_JOB_COMPLETED);
> > }
> >
> > +static void qemuMonitorJSONHandleBlockJobCancelled(qemuMonitorPtr mon,
> > + virJSONValuePtr data)
> > +{
> > + qemuMonitorJSONHandleBlockJobImpl(mon, data, VIR_DOMAIN_BLOCK_JOB_CANCELLED);
> > +}
> >
> > int
> > qemuMonitorJSONHumanCommandWithFd(qemuMonitorPtr mon,
> > --
> > 1.7.5.rc1
> >
>
--
Adam Litke <agl@xxxxxxxxxx>
IBM Linux Technology Center
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