[libvirt] [PATCH 6/7] storage:dir: adapts .refreshVol .refreshPool for ploop volumes

[Ján Tomko]

On Wed, Apr 06, 2016 at 11:18:22AM +0300, Olga Krishtal wrote:
> On 05/04/16 18:01, Ján Tomko wrote:
> > On Mon, Mar 14, 2016 at 07:00:39PM +0300, Olga Krishtal wrote:
> >> Refreshes meta-information such as allocation, capacity, format, etc.
> >> Ploop volumes differ from other volume types. Path to volume is the path
> >> to directory with image file root.hds and DiskDescriptor.xml.
> >> https://openvz.org/Ploop/format
> >> Due to this fact, operations of opening the volume have to be done once
> >> again. get the information.
> >>
> >> To decide whether the given volume is ploops one, it is necessary to check
> >> the presence of root.hds and DiskDescriptor.xml files in volumes' directory.
> >> Only in this case the volume can be manipulated as the ploops one.
> >> Such strategy helps us to resolve problems that might occure, when we
> >> upload some other volume type from ploop source.
> >>
> >> Signed-off-by: Olga Krishtal <okrishtal at virtuozzo.com>
> >> ---
> >>   src/storage/storage_backend.c    | 62 ++++++++++++++++++++++++++++++++++++--
> >>   src/storage/storage_backend.h    |  5 ++++
> >>   src/storage/storage_backend_fs.c | 64 +++++++++++++++++++++++++++++++++++++---
> >>   src/util/virstoragefile.c        |  7 +++--
> >>   4 files changed, 129 insertions(+), 9 deletions(-)
> >>
> >> @@ -69,6 +109,7 @@ virStorageBackendProbeTarget(virStorageSourcePtr target,
> >>       int fd = -1;
> >>       int ret = -1;
> >>       int rc;
> >> +    int format = VIR_STORAGE_FILE_AUTO;
> >>       virStorageSourcePtr meta = NULL;
> >>       struct stat sb;
> >>   
> >> @@ -84,14 +125,26 @@ virStorageBackendProbeTarget(virStorageSourcePtr target,
> >>           goto cleanup;
> >>   
> >>       if (S_ISDIR(sb.st_mode)) {
> >> -        target->format = VIR_STORAGE_FILE_DIR;
> >> -        ret = 0;
> >> -        goto cleanup;
> >> +        if (virStorageBackendIsPloopDir(target->path)) {
> >> +            if (virStorageBackendRedoPloopUpdate(target, &sb, &fd,
> >> +                                                 VIR_STORAGE_VOL_FS_PROBE_FLAGS)
> >> +                < 0)
> >> +                goto cleanup;
> >
> >> +            /* Refresh information stored in DiskDescriptor.xml according
> >> +             * to ploop image file content.*/
> >> +            if (virStorageBackendPloopRestoreDesc(target->path) < 0)
> >> +                goto cleanup;
> > Probing a volume should not change its contents - libvirt should only
> > refresh this XML when it changed the volume.
> >
> > The rest looks good to me.
> >
> > Jan
> The thing is that if we changed the size, the content of root.hds and 
> had left the old DiskDeskriptor.xml - it becomes impossible to operate.
> I mean that DiskDescriptor.xml stores this info - size, Celinders, 
> Sectors, and what is more important - all information about snapshot.
> In the situation when we have uploaded previously snapshoted volume - 
> the content of volume and DiskDescriptor will be inconsistent.
> And work upon such volume will be impossible.
> But if you have any idea, where such refresh of DiskDescriptor.xml could 
> be done - I will be glad to know.

DiskDeskriptor should be changed at the same time as root.hds -
if libvirt does the resize/content change, it should refresh the XML as
part of the API that changes the volume.

Libvirt's pool refresh or vol refresh should only update libvirtd's
in-memory metadata to match the on-disk state.

If the on-disk state was left inconsistent by some other application,
it's a problem of that application. I don't think libvirt should be
working around that.

Jan