[Libvir] [Libvirt] Proposal to add 3 functions for VBDs (Virtual Block Devices)

[Daniel Veillard]

On Thu, Aug 24, 2006 at 05:32:19PM +0200, michel.ponceau at bull.net wrote:
> After the new VCPU functions, we also need Virtual Block Device management 
> equivalent to Xen commands:
>     'xm block-list', 'xm block-attach', 'xm block-detach'.
> I propose to add in Libvirt the following 3 functions:
> /**
>  * virDomainGetVbdevs:
>  * @domain: pointer to domain object, or NULL for Domain0
>  * @info: pointer to an array of virVbdevInfo structures
>  * @maxinfo: number of structures in info array
>  * 
>  * Extract information about virtual block devices of domain, store it in 
> info.
>  *
>  * Returns the number of info filled in case of success, -1 in case of 
> failure.
>  */
> int virDomainGetVbdevs(virDomainPtr domain, virVbdevInfoPtr info, int 
> maxinfo)
> 
> /**
>  * virDomainCreateVbdev:
>  * @domain: pointer to domain object, or NULL for Domain0
>  * @number: virtual device number
>  * @mode: read-only (VIR_VBDMD_RO), or read/write (VIR_VBDMD_RW)
>  * @bkendID: ID of domain hosting the backend device (usually 0 for 
> domain0)
>  * @bkend: pointer to backend device path
>  * 
>  * Create a virtual block device.
>  *
>  * Returns 0 in case of success, -1 in case of failure.
>  */
> int virDomainCreateVbdev(virDomainPtr domain, unsigned int number, int 
> mode,
>                      int bkendID, char *bkend)
> 
> /**
>  * virDomainDestroyVbdev:
>  * @domain: pointer to domain object, or NULL for Domain0
>  * @number: virtual device number
>  * 
>  * Destroy a virtual block device.
>  *
>  * Returns 0 in case of success, -1 in case of failure.
>  */
> int virDomainDestroyVbdev(virDomainPtr domain, unsigned int number)

  Humm, my concern here is how general is that API ? bkendID is certainly
a Xen'ism, with no equivalent in other virtualization frameworks. If we 
add dynamic block devices creation and destruction, it must be clear what
those operation means outside of a pure Xen context. In general devices
are not named by one number, bkendID is a xen concept, I don't see why
it should appear as is in the API.

> Structure in libvirt.h:
> /**
>  * virVbdevInfo: information structure for a Virtual Block Device in a 
> domain
>  */
> typedef struct _virVbdevInfo virVbdevInfo;
> struct _virVbdevInfo {
>     unsigned int number;        /* virtual device number */
>     int state;
>     int evtChn;
>     int ringRef;
>     int bkendID;                /* ID of domain hosting the backend device 
> */
>     char bkend[128];
> };
> typedef virVbdevInfo *virVbdevInfoPtr;

  Way way too Xen specific, too undefined in general, as is this really
cannot show up in libvirt API. I would prefer discussing the concept of 
the operation first instead of starting from a Xen standpoint and trying to
make it an API.
  What are conceptually the operations you want to do ? How would you name 
the objects exposed in those oeprations ?

Daniel

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