Re: [libvirt] [PATCH 1/6] Add new API virDomainStreamDisk[Info] to header and drivers
On 04/08/2011 07:31 AM, Daniel P. Berrange wrote:
On Thu, Apr 07, 2011 at 04:31:59PM -0500, Adam Litke wrote:
> /*
> + * Disk Streaming
> + */
> +typedef enum {
> + VIR_STREAM_DISK_ONE = 1, /* Stream a single disk unit */
> + VIR_STREAM_DISK_START = 2, /* Stream the entire disk */
> + VIR_STREAM_DISK_STOP = 4, /* Stop streaming a disk */
> +} virDomainStreamDiskFlags;
Using flags to combine two separate tasks into one single API
is rather unpleasant. As raised in the previous patch, the API
should also be taking a offset+length in bytes, then there is
no need for a special case transfer of an individual sector.
Taking all the previous points together, I think the API needs to
look like this:
typedef enum {
/* If set, virDomainBlockAllocate() will return immediately
* allowing polling for operation completion & status
*/
VIR_DOMAIN_DISK_ALLOCATE_NONBLOCK,
} virDomainBlockAllocateFlags;
It seems like adding one more flag would also make this API useful for
supporting the converse operation: if we have a disk that is currently
allocated, but we either know that a block is all 0s (or don't care
about the data in that block if it was not all 0s), it would be nice to
request punching a hole (for file-backed images residing on a file
system and kernels new enough to do that) and/or truncate back to a
smaller (thinly-provisioned) allocated size (which should work for both
file-backed and lvm-backed disk images).
Meanwhile, I know that GNU coreutils has been working on an API for
efficiently getting FIEMAP data from files; part of this effort needs to
involve migrating that code into gnulib so that libvirt can indeed
provide an API that enumerates sections of a disk image that are
allocated vs. holes.
--
Eric Blake eblake(a)redhat.com +1-801-349-2682
Libvirt virtualization library http://libvirt.org
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