On Thu, Sep 03, 2020 at 12:18:42PM +0200, Christian Ehrhardt wrote:
On Wed, Sep 2, 2020 at 6:49 PM Michal Privoznik <mprivozn@redhat.com> wrote:
On 9/2/20 3:58 PM, Christian Ehrhardt wrote:
In c9ec7088 "storage: extend preallocation flags support for qemu-img" the option to fallocate was added and meant to be active when (quote): "the XML described storage <allocation> matches its <capacity>"
Up until recently 81a3042a12 "storage_util: fix qemu-img sparse allocation" the compared allocation size was an order of magnitude too small, but still it does use fallocate too often unless capacity>allocation.
This change fixes the comparison to match the intended description of the feature.
Fixes: c9ec7088c7a3f4cd26bb471f1f243931fff6f4f9 Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1759454 Fixes: https://bugs.launchpad.net/ubuntu/focal/+source/libvirt/+bug/1847105
Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com> --- src/storage/storage_util.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
And sorry for making the mess earlier (~2 years ago).
no problem - it turned out to be even more confusing.
Due to some further testing and encouraged by feedback in the same direction by Richard Lager (on CC now) I realized that while the suggested change reads correct it will still not help my case :-/
Even if my fix lands, we are back to square one and would need virt-manager to submit a different XML. Remember: my target here would be to come back to pralloca=metadata as it was before for image creations from virt-manager. I've started that aspect of the discussion at the BZ [1] already.
On the libvirt side allocation>capacity sounds like being wrong anyway.
It is a bit wierd as an input XML from a mgmt app. It is to be expected as an output XML from libvirt though. Some filesystems, notably XFS, will sometimes speculatively over-allocate data extents in the belief that further size-extending writes will probably arrive. So you can end up with allocated blocks being greater than the current logical file size.
And if that is so we have these possible conditions: - capacity==allocation now and before my change falloc - capacity>allocation now and before my change metadata - capacity<allocation before my change falloc, afterwards metadata (but this one seems invalid anyway)
So I wonder are we really back at me asking Cole to let virt-manager request things differently which is how this started about a year ago? Or was I wrong trying to make the code to match the wording in the commit that added it and do we actually want it to behave differently (read no falloc) for the XMLs sent by virt-manager as of today?
I think we should provide three flags VIR_STORAGE_VOL_CREATE_PREALLOC_METADATA VIR_STORAGE_VOL_CREATE_PREALLOC_NONE VIR_STORAGE_VOL_CREATE_PREALLOC_PAYLOAD as a way to get explicit behaviour, with those flags ignoring the "allocation" field. Only look at "allocation" if none of the flags are given for sake of back compat. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|