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

24 Aug 2006


      On Thu, Aug 24, 2006 at 05:32:19PM +0200, michel.ponceau@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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