Re: [PATCH] migration: Truncate state file in xen-save-devices-state

[Marek Marczykowski-Górecki]

On Mon, Sep 28, 2020 at 05:46:18PM +0100, Anthony PERARD wrote:
> On Mon, Sep 21, 2020 at 12:17:23PM +0100, Dr. David Alan Gilbert wrote:
> > * Dov Murik (dovmurik@linux.vnet.ibm.com) wrote:
> > > When running the xen-save-devices-state QMP command, if the filename
> > > already exists it will be truncated before dumping the devices' state
> > > into it.
> > > 
> > > Signed-off-by: Dov Murik <dovmurik@linux.vnet.ibm.com>
> > > ---
> > >  migration/savevm.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/migration/savevm.c b/migration/savevm.c
> > > index 304d98ff78..e1b26672cc 100644
> > > --- a/migration/savevm.c
> > > +++ b/migration/savevm.c
> > > @@ -2803,7 +2803,8 @@ void qmp_xen_save_devices_state(const char 
> > > *filename, bool has_live, bool live,
> > >      vm_stop(RUN_STATE_SAVE_VM);
> > >      global_state_store_running();
> > >  
> > > -    ioc = qio_channel_file_new_path(filename, O_WRONLY | O_CREAT, 0660, 
> > > errp);
> > > +    ioc = qio_channel_file_new_path(filename, O_WRONLY | O_CREAT | 
> > > O_TRUNC,
> > > +                                    0660, errp);
> > >      if (!ioc) {
> > >          goto the_end;
> > >      }
> 
> Hi Marek,
> 
> Do you know if the above patch is going to work in a linux stubdomain?
> Can we truncate the "save file" which seems to be stubdomain's console 1?

No, truncate won't work on the stubdomain's console. I mean, the
operation won't fail, but the actual file connected to the console on
the other end won't get truncated. But I think in case of stubdomain,
toolstack should connect the console to an empty file, so it shouldn't
be a problem.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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