[libvirt] [PATCH v2 2/4] qemu: block: use the delete flag to delete snapshot images if requested

[Peter Krempa]

On Wed, Nov 20, 2019 at 14:56:18 +0100, Pavel Mores wrote:
> On Wed, Nov 20, 2019 at 12:11:32PM +0100, Peter Krempa wrote:
> > On Wed, Nov 20, 2019 at 11:44:53 +0100, Pavel Mores wrote:
> > > When blockcommit finishes successfully, one of the
> > > qemuBlockJobProcessEventCompletedCommit() and
> > > qemuBlockJobProcessEventCompletedActiveCommit() event handlers is called.
> > > This is where the delete flag (stored in qemuBlockJobCommitData since the
> > > previous commit) can actually be used to delete the committed snapshot
> > > images if requested.
> > > 
> > > Signed-off-by: Pavel Mores <pmores at redhat.com>
> > > ---
> > >  src/qemu/qemu_blockjob.c | 31 +++++++++++++++++++++++++++++++
> > >  1 file changed, 31 insertions(+)
> > > 
> > > diff --git a/src/qemu/qemu_blockjob.c b/src/qemu/qemu_blockjob.c
> > > index 7d94a6ce38..cf221a2839 100644
> > > --- a/src/qemu/qemu_blockjob.c
> > > +++ b/src/qemu/qemu_blockjob.c
> > > @@ -965,6 +965,31 @@ qemuBlockJobProcessEventCompletedPull(virQEMUDriverPtr driver,
> > >  }
> > >  
> > >  
> > > +/**
> > > + * Helper for qemuBlockJobProcessEventCompletedCommit() and
> > > + * qemuBlockJobProcessEventCompletedActiveCommit().  Relies on adjustments
> > > + * these functions perform on the 'backingStore' chain to function correctly.
> > > + *
> > > + * TODO look into removing backing store for non-local snapshots too
> > > + */
> > > +static void
> > > +qemuBlockJobUnlinkCommittedStorage(virStorageSourcePtr top)
> > > +{
> > > +    virStorageSourcePtr p = top;
> > > +    const size_t errmsg_len = 128;
> > > +    char errmsg_buf[errmsg_len];
> > > +    char *errmsg;
> > > +
> > > +    for (; p != NULL; p = p->backingStore) {
> > > +        if (virStorageSourceIsLocalStorage(p))
> > 
> > The above condition has a multiline body, so it must be enclosed in a
> > block.
> > 
> > > +            if (unlink(p->path) < 0) {
> > 
> > I was considering whether we should use virFileRemove which will also
> > work properly on root-squashed NFS. I'm not sure though how easy it will
> > be to figure out the correct uid and gid inside this helper.
> > 
> > If you are interrested into investigating if it's possible, there should
> > be some prior art in the qemu driver where we try to get the uid/gid frm
> > virStorageSource if it's configured, then fall back to the domain
> > uid/gid of the process.
> 
> I can see qemuDomainGetImageIds() in qemu_domain.c which seems somewhat close

yes, this is the one I meant! I couldn't remember :D

> to what you describe.  It tries to get uid/gid from the virStorageSourcePtr
> itself, then its parent virStorageSourcePtr, then virDomainObjPtr and
> finally virQEMUDriverConfigPtr.

That is the correct hierarchy. An image file can either have it's own
security label, or the security label of the disk applies to all of the
chain members, if the disk doesn't have a label there is a default label
for the whole VM and in case that isn't available in case of the DAC
driver we apply the configured uid/gid.

> It's static in its file though, and I don't immediately see an easy way to pass
> it the virQEMUDriverConfigPtr.  However, if it's OK to make it visible from

I think it's okay to export it.

> blockdev code, I could still call it along the lines of

You can get the config via:

virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);

and driver via:

virQEMUDriverPtr driver = priv->driver;

and finally:

qemuDomainObjPrivatePtr priv = vm->privateData;

Since qemuDomainGetImageIds already takes vm, I'd suggest you refactor
it or add a wrapper which will not require passing of 'cfg', but will
acquire it via the above mentioned method from vm, so that we don't have
to do it in the blockjob code.

> 	qemuDomainGetImageIds(NULL, vm, p, NULL, &uid, &gid);
> 
> as I can apparently get a virDomainObjPtr into the helper quite easily.
> 
> > > +                errmsg = strerror_r(errno, errmsg_buf, errmsg_len);
> > 
> > Please use g_strerror(); It does not require any of the buffers and
> > stuff.
> > 
> > > +                VIR_WARN("Unable to remove snapshot image file %s (%s)",
> > > +                         p->path, errmsg);
> > > +            }
> > > +    }
> > 
> > The rest looks good.
> > 
> 
> --
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