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Re: [libvirt] API Proposal: virDomainBlockPull() (Block device streaming) V4



On Tue, May 24, 2011 at 07:36:36AM -0500, Adam Litke wrote:
> 
> 
> On 05/24/2011 07:19 AM, Daniel P. Berrange wrote:
> > On Mon, May 23, 2011 at 11:56:03AM -0500, Adam Litke wrote:
> >> Here is version 4 of the BlockStream API (now called BlockPull).  Hopefully this
> >> version addresses all remaining concerns and I can begin to work on the code.
> >> Does everyone approve of the new name 'virDomainBlockPull'?
> >>
> >>
> >> Changes since V3:
> >>  - Renamed the API to 'Block Pull' to emphasize the effect of the API over its
> >>    method of operation.
> >>  - Changed virDomainGetBlockPullInfo() to accept a path argument and to return
> >>    information about that path alone.
> >>  - Added a new virDomainEvent to report final status when using CONTINUOUS mode.
> >>
> >> /*
> >>  * Block Pull API
> >>  */
> >> typedef enum {
> >>     /*
> >>      * If set, virDomainBlockPull() will operate on the entire device in the
> >>      * background.  The status can be checked and the operation aborted by
> >>      * using the functions virDomainBlockPullInfo() and
> >>      * virDomainBlockPullAbort().
> >>      */
> >>     VIR_DOMAIN_BLOCK_PULL_CONTINUOUS = 1,
> >> } virDomainBlockPullFlags;
> >>
> >> /* An iterator for initiating and monitoring block pull operations */
> >> typedef unsigned long long virDomainBlockPullCursor;
> >>
> >> typedef struct _virDomainBlockPullInfo virDomainBlockPullInfo;
> >> struct _virDomainBlockPullInfo {
> >>     /*
> >>      * The following fields provide an indication of block pull progress.  @cur
> >>      * indicates the current position and will be between 0 and @end.  @end is
> >>      * the final cursor position for this operation and represents completion.
> >>      * To approximate progress, divide @cur by @end.
> >>      */
> >>     virDomainBlockPullCursor cur;
> >>     virDomainBlockPullCursor end;
> >> };
> >> typedef virDomainBlockPullInfo *virDomainBlockPullInfoPtr;
> >>
> >> /**
> >>  * virDomainBlockPull:
> >>  * @dom: pointer to domain object
> >>  * @path: Fully-qualified filename of disk 
> >>  * @cursor: pointer to a virDomainBlockPullCursor, or NULL
> >>  * @flags: One of virDomainBlockPullFlags, or zero
> >>  *
> >>  * Populate a disk image with data from its backing image.  Once all data from
> >>  * its backing image has been pulled, the disk no longer depends on a backing
> >>  * image.
> >>  *
> >>  * If VIR_DOMAIN_BLOCK_PULL_CONTINUOUS is specified, the entire device will be
> >>  * streamed in the background.  Otherwise, the value stored in @cursor will be
> >>  * used to stream an increment.
> >>  *
> >>  * Returns -1 in case of failure, 0 when successful.  On success and when @flags
> >>  * does not contain VIR_DOMAIN_BLOCK_PULL_CONTINUOUS, the iterator @cursor will
> >>  * be updated to the proper value for use in a subsequent call.
> >>  */
> >> int                 virDomainBlockPull(virDomainPtr dom,
> >>                                        const char *path,
> >>                                        virDomainBlockPullCursor *cursor,
> >>                                        unsigned int flags);
> >>
> >> /**
> >>  * virDomainBlockPullAbort:
> >>  * @dom: pointer to domain object
> >>  * @path: fully-qualified filename of disk
> >>  * @flags: currently unused, for future extension
> >>  *
> >>  * Cancel a pull operation that has been previously started by a call to
> >>  * virDomainBlockPull() with the VIR_DOMAIN_BLOCK_PULL_CONTINUOUS flag.
> >>  *
> >>  * Returns -1 in case of failure, 0 when successful.
> >>  */
> >> int                 virDomainBlockPullAbort(virDomainPtr dom,
> >>                                             const char *path,
> >>                                             unsigned int flags);
> >>
> >> /**
> >>  * virDomainGetBlockPullInfo:
> >>  * @dom: pointer to domain object
> >>  * @path: fully-qualified filename of disk
> >>  * @info: pointer to a virDomainBlockPullInfo structure
> >>  * @flags: currently unused, for future extension
> >>  *
> >>  * Request progress information on a block pull operation that has been started
> >>  * with the VIR_DOMAIN_BLOCK_PULL_CONTINUOUS flag set.  If an operation is
> >>  * active for the given parameters, @info will be updated with the current
> >>  * progress.
> >>  *
> >>  * Returns -1 in case of failure, 0 when successful.
> >>  */
> >> int                 virDomainGetBlockPullInfo(virDomainPtr dom,
> >>                                               const char *path,
> >>                                               virDomainBlockStreamInfoPtr info,
> >>                                               unsigned int flags);
> >>
> >>
> >> The following new asynchronous event will be made available for subscription:
> >>
> >> VIR_DOMAIN_EVENT_ID_BLOCK_PULL = 7,
> >>
> >> typedef enum {
> >>     VIR_DOMAIN_BLOCK_PULL_COMPLETED,
> >>     VIR_DOMAIN_BLOCK_PULL_FAILED,
> >> } virConnectDomainEventBlockPullStatus;
> >>
> >> typedef void (*virConnectDomainEventBlockPullCallback(virConnectPtr conn,
> >>                                                       virDomainPtr dom,
> >>                                                       const char *path,
> >>                                                       int status);
> >>
> >> Upon receipt of this event and when the status field indicates success, libvirt
> >> will revoke access to the backing file which is no longer needed by the domain.
> >>
> >> NOTE: Qemu will emit an asynchronous event (VIR_DOMAIN_BLOCK_PULL_COMPLETED)
> >> after any operation that eliminates the dependency on the backing file.  This
> >> could be a virDomainBlockPull() without VIR_DOMAIN_BLOCK_PULL_CONTINUOUS and
> >> will allow libvirt to manage backing file security regardless of the pull mode
> >> used.
> > 
> > I assume it will also emit VIR_DOMAIN_BLOCK_PULL_FAILED when a continuous
> > streaming operation aborts, because in that case you obviously still have
> > the backing file present so PULL_COMPLETED wouldn't be issued ?
> 
> I don't think abort is the same as failed in this case.  An abort is
> triggered by the API user whereas a failure is not.  If a user issues an
> abort, they should know to stop waiting around for PULL_COMPLETED.  A
> failure is unexpected and thus absolutely needs an event to be raised.

Sorry, mixed language there. When I said 'streaming operation aborts' I
meant a QEMU initiated abort due to some storage failure, not an admin/app
requested abort via the API. So we're in agreement.


Daniel
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