Re: [libvirt] [PATCH v2 02/12] qemu: let blockinfo reuse virStorageSource

On 12/16/14 09:04, Eric Blake wrote: > Right now, grabbing blockinfo always calls stat on the disk, then > opens the image to determine the capacity, using a throw-away > virStorageSourcePtr. This has a couple of drawbacks: >

> > While this patch does not optimize reuse of information in point > 1, it does get us closer to being able to do so; by updating a > structure that survives between consecutive calls. >

> > + /* FIXME: For an offline domain, we always want to check current > + * on-disk statistics (as users have been known to change offline > + * images behind our backs). For a running domain, however, it > + * would be nice to avoid opening a file (particularly since > + * reading a file while qemu is writing it risks the reader seeing > + * bogus data), or even avoid a stat, if the information > + * remembered from the previous run is still viable. > + * > + * For read-only disks, nothing should be changing unless the user > + * has requested a block-commit action. For read-write disks, we > + * know some special cases: capacity should not change without a > + * block-resize (where capacity is the only stat that requires > + * opening a file, and even then, only for non-raw files); and > + * physical size of a raw image or of a block device should > + * likewise not be changing without block-resize. On the other > + * hand, allocation of a raw file can change (if the file is > + * sparse, but the amount of sparseness changes due to writes or > + * punching holes), and physical size of a non-raw file can > + * change. > + */ I still don't see this comment vanishing in this series. Are you planing on getting rid of the code that opens the file on disk while the VM is alive?

> if (virStorageSourceIsLocalStorage(disk->src)) { > if (!disk->src->path) { > virReportError(VIR_ERR_INVALID_ARG, ACK