[libvirt] RFC New virDomainBlockPull API family to libvirt

[Jiri Denemark]

On Thu, Jul 14, 2011 at 10:58:31 +0100, Stefan Hajnoczi wrote:
> On Thu, Jul 14, 2011 at 10:21 AM, Jiri Denemark <jdenemar at redhat.com> wrote:
> > On Wed, Jul 13, 2011 at 15:46:30 -0500, Adam Litke wrote:
> > ...
> >> /*
> >>  * BlockPull API
> >>  */
> >>
> >> /* 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;
> > ...
> >> /**
> >>  * virDomainBlockPullAbort:
> >>  * @dom: pointer to domain object
> >>  * @path: fully-qualified filename of disk
> >>  * @flags: currently unused, for future extension
> >>  *
> >>  * Cancel a pull operation previously started by virDomainBlockPullAll().
> >>  *
> >>  * 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 virDomainBlockPull().  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,
> >>                                               virDomainBlockPullInfoPtr info,
> >>                                               unsigned int flags);
> >>
> >> /**
> >>  * virConnectDomainEventBlockPullStatus:
> >>  *
> >>  * The final status of a virDomainBlockPull() operation
> >>  */
> >> typedef enum {
> >>     VIR_DOMAIN_BLOCK_PULL_COMPLETED = 0,
> >>     VIR_DOMAIN_BLOCK_PULL_FAILED = 1,
> >> } virConnectDomainEventBlockPullStatus;
> >>
> >> /**
> >>  * virConnectDomainEventBlockPullCallback:
> >>  * @conn: connection object
> >>  * @dom: domain on which the event occurred
> >>  * @path: fully-qualified filename of the affected disk
> >>  * @status: final status of the operation (virConnectDomainEventBlockPullStatus
> >>  *
> >>  * The callback signature to use when registering for an event of type
> >>  * VIR_DOMAIN_EVENT_ID_BLOCK_PULL with virConnectDomainEventRegisterAny()
> >>  */
> >> typedef void (*virConnectDomainEventBlockPullCallback)(virConnectPtr conn,
> >>                                                        virDomainPtr dom,
> >>                                                        const char *path,
> >>                                                        int status,
> >>                                                        void *opaque);
> >
> > Could these managing functions and event callback become general and usable by
> > other block operations such as block copy?
> 
> Hi Jiri,
> Live block copy will certainly be possible using the streaming API.
> Before you start streaming you need to use the snapshot_blkdev command
> to create the destination file with the source file as its backing
> image.  You can then use the streaming API to copy data from the
> source file into the destination file.  On completion the source file
> is no longer needed.

Well, I'm not talking about using the same API for block copy or implementing
block copy internally as block streaming. I'm talking about making GetInfo,
Abort and event callback general to be usable not only for block streaming or
block copy but also for other possible block operations in the future.

The reason is that starting a block operation (streaming, copy, whatever) may
need different parameters so they should be different APIs. But once the
operation is started, we just need to know how far it got and we need the
ability to abort the job. So this can share the same APIs for all operations.
It doesn't make sense to require any block operation to provide their own set
of managing APIs.

It's analogous to virDomainSave, virDomainMigrate, virDomainCoreDump. They are
all different jobs but all of them can be monitored and aborted using
virDomainGetJobInfo and virDomainAbortJob.

Jirka