On 12/16/2014 05:41 AM, Peter Krempa wrote:
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?
Correct, that's where my other email (subject "virDomainGetBlockInfo meanings") would come into play - I'm still trying to work on additional patches to reuse code correctly and minimize file probes where possible, but those can be followup patches. So I will go ahead and push the patches that have been ACKed so far.
if (virStorageSourceIsLocalStorage(disk->src)) { if (!disk->src->path) { virReportError(VIR_ERR_INVALID_ARG,
ACK
Thanks for the reviews :) -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org