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Re: [libvirt] [PATCH v4 2/4] storage: report error rather than warning if backing files doesn't exist



On Tue, Jul 16, 2013 at 08:14:54AM +0200, Martin Kletzander wrote:
> On 07/15/2013 05:31 PM, Ján Tomko wrote:
> > On 07/02/2013 11:35 AM, Guannan Ren wrote:
> >> If one of backing files for disk source doesn't exist, the guest will not
> >> be able to find and use the disk even though the disk still exists in
> >> guest xml definition. So reporting an error make more sense.
> >>
> >> Adding virFileAccessibleAs() to check if the backing file described in
> >> disk meta exist in real path. If not, report error. the uid and gid
> >> arguments don't have so much meannings for F_OK, so give 0 for them.
> >> ---
> >>  src/util/virstoragefile.c | 23 +++++++++++++++--------
> >>  tests/virstoragetest.c    | 16 ++++++++--------
> >>  2 files changed, 23 insertions(+), 16 deletions(-)
> >>
> >> diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c
> >> index 27aa4fe..cb61e5b 100644
> >> --- a/src/util/virstoragefile.c
> >> +++ b/src/util/virstoragefile.c
> > 
> >> @@ -870,14 +877,10 @@ virStorageFileGetMetadataInternal(const char *path,
> >>                                         !!directory, backing,
> >>                                         &meta->directory,
> >>                                         &meta->backingStore) < 0) {
> >> -                    /* the backing file is (currently) unavailable, treat this
> >> -                     * file as standalone:
> >> -                     * backingStoreRaw is kept to mark broken image chains */
> >> -                    meta->backingStoreIsFile = false;
> >> -                    backingFormat = VIR_STORAGE_FILE_NONE;
> >> -                    VIR_WARN("Backing file '%s' of image '%s' is missing.",
> >> -                             meta->backingStoreRaw, path);
> >> -
> >> +                    VIR_ERROR(_("Backing file '%s' of image '%s' is missing."),
> >> +                              meta->backingStoreRaw, path);
> >> +                    VIR_FREE(backing);
> >> +                    goto cleanup;
> >>                  }
> >>              }
> >>              VIR_FREE(backing);
> > 
> > This change means you won't be able to start the pool if one of the files is
> > missing a backing file. I've forwarded a patch [1] from/for [2] that ignores
> > missing files on pool start and there is a bug [3] requesting that we ignore
> > other files as well. I feel like this is going in the other direction.
> > 
> > Wouldn't it be enough to check for them on domain start-up and leave the pool
> > running even if one of those volumes doesn't have an existing backing file?
> > 
> 
> How about making it configurable for the pool?  There are definitely
> some users who want the pool to reflect actual info after pool-refresh.

I don't think this needs to be configurable. The pool should show *every*
single file, regardless of whether the file has a broken backing file.
We shouldn't be trying to second guess what the user wants to do with a
image with broken backing file. Just expose as much info as we have and
let them deal with the problem.

Daniel
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