[libvirt] [PATCH] virsh: fixed handling of targetless disks (e.g. empty CDROM) in 'domblkinfo' cmd

[Pavel Mores]

On Thu, Oct 03, 2019 at 01:09:55PM +0200, Pavel Mores wrote:
> On Thu, Oct 03, 2019 at 11:54:44AM +0200, Ján Tomko wrote:
> > On Wed, Oct 02, 2019 at 04:21:52PM +0200, Pavel Mores wrote:
> > > On Wed, Oct 02, 2019 at 08:34:10AM -0300, Daniel Henrique Barboza wrote:
> > > > 
> > > > 
> > > > On 10/1/19 11:45 AM, Pavel Mores wrote:
> > > > > virDomainGetBlockInfo() returns error if called on a disk with no target
> > > > > (a targetless disk might be a removable media drive with no media in it,
> > > > > for instance an empty CDROM drive).
> > > > >
> > > > > So far this caused the virsh domblkinfo --all command to abort and ignore
> > > > > any remaining (not yet displayed) disk devices.  This patch fixes it by
> > > > > ignoring virDomainGetBlockInfo() errors for CDROM and floppy drives,
> > > > > similar to how it's done for network drives.
> > > > >
> > > > > https://bugzilla.redhat.com/show_bug.cgi?id=1619625
> > > > >
> > > > > Signed-off-by: Pavel Mores <pmores at redhat.com>
> > > > > ---
> > > > >   tools/virsh-domain-monitor.c | 11 +++++++++++
> > > > >   1 file changed, 11 insertions(+)
> > > > >
> > > > > diff --git a/tools/virsh-domain-monitor.c b/tools/virsh-domain-monitor.c
> > > > > index 0e2c4191d7..0f495c1a3f 100644
> > > > > --- a/tools/virsh-domain-monitor.c
> > > > > +++ b/tools/virsh-domain-monitor.c
> > > > > @@ -473,6 +473,7 @@ cmdDomblkinfo(vshControl *ctl, const vshCmd *cmd)
> > > > >       char *cap = NULL;
> > > > >       char *alloc = NULL;
> > > > >       char *phy = NULL;
> > > > > +    char *device_type = NULL;
> > > > 
> > > > I believe you need to use VIR_AUTO(char *) here. Even considering that
> > > > the macro will be deprecated in the near future for glib stuff, by using
> > > > VIR_AUTO here:
> > > > 
> > > > - you'll make it easier to introduce the glib replacement, since
> > > > s/VIR_AUTO/<g_lib_macro> is a trivial change;
> > > > 
> > > > - you won't be adding more VIR_FREE() on top of existing cases that will
> > > > need to be addressed in the future.
> > > 
> > > Was that the consensus from the migration debate?  If so I'm happy to fix my
> > > patch.
> > 
> > IIUC the consensus was that we will switch to g_auto eventually,
> > but it's a simple string replace that will be dealt with by whoever
> > pushes the patch.
> > 
> > Also, if you go with any of the two approaches I suggested (ignoring all
> > errors or using the XPathBoolean), you don't need to introduce a new
> > allocated variable
> 
> Cool, so if there aren't any objections, I'll implement the XPathBoolean
> variant and submit v2.

As it turns out, the thing with the virDomainGetBlockInfo() call is that even
if it fails, it does initialise the virDomainBlockInfo structure enough to be
displayed in the table (even if just as a target name and dashes).

It follows apparently that if we go the virXPathBoolean() way and skip the
virDomainGetBlockInfo() call, we can't show the sourceless device at all, we
can't even indicate that it exists.

Is that acceptable?  Or is there another way to fill in virDomainBlockInfo?

Thanks,

	pvl