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.