[libvirt] [PATCH 1/3] virfile: Provide stub for virFileInData

[Daniel P. Berrange]

On Fri, May 19, 2017 at 01:31:32PM +0200, Michal Privoznik wrote:
> On 05/19/2017 12:28 PM, Peter Krempa wrote:
> > On Thu, May 18, 2017 at 15:46:44 +0200, Michal Privoznik wrote:
> >> Some older systems (such as RHEL6) lack SEEK_HOLE and SEEK_DATA
> >> which virFileInData relies on. Provide a stub for these systems.
> >>
> >> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> >> ---
> >>  configure.ac       |  5 +++++
> >>  src/util/virfile.c | 15 +++++++++++++++
> >>  2 files changed, 20 insertions(+)
> > 
> > [...]
> > 
> >> @@ -3904,6 +3905,20 @@ virFileInData(int fd,
> >>      return ret;
> >>  }
> >>  
> >> +#else /* !HAVE_DECL_SEEK_HOLE */
> >> +
> >> +int
> >> +virFileInData(int fd ATTRIBUTE_UNUSED,
> >> +              int *inData ATTRIBUTE_UNUSED,
> >> +              long long *length ATTRIBUTE_UNUSED)
> >> +{
> >> +    virReportSystemError(ENOSYS, "%s",
> >> +                         _("sparse files not supported"));
> >> +    return -1;
> > 
> > Wouldn't it be better as a fallback always return that data is present
> > rather than failing?
> > 
> 
> I don't think so. What I can do actually is to not only report error,
> but also set errno = ENOSYS, so that caller can distinguish this case
> from other cases where virFileInData fails. I think we should let it up
> to the caller to decide then whether they want to ignore the error (and
> pretend there are no holes), or fail too. More generally, helpers in
> src/util/ should really be one purpose functions without trying to be
> clever and leave the logic for callers (drivers).

In particular by reporting an error we give options to the mgmt application.
They may well *not* want to do the upload/download if there is no sparse
support. By reporting an error they can detect that and make a decision
as to whether to retry without sparse flag enabled or not.


Regards,
Daniel
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