Re: [Xen-devel] [RFC PATCH 2/6] libxl: stop using libxl__xs_mkdir() for ~/control/shutdown

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Ian Campbell [mailto:ian.campbell@xxxxxxxxxx]
> Sent: 25 November 2015 10:43
> To: Paul Durrant; Ian Jackson
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Stefano Stabellini; Wei Liu
> Subject: Re: [RFC PATCH 2/6] libxl: stop using libxl__xs_mkdir() for
> ~/control/shutdown
> 
> On Tue, 2015-11-24 at 17:20 +0000, Paul Durrant wrote:
> > > -----Original Message-----
> > > From: Ian Jackson [mailto:Ian.Jackson@xxxxxxxxxxxxx]
> > > Sent: 24 November 2015 16:35
> > > To: Paul Durrant
> > > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Stefano Stabellini; Ian Campbell;
> > > Wei Liu
> > > Subject: RE: [RFC PATCH 2/6] libxl: stop using libxl__xs_mkdir() for
> > > ~/control/shutdown
> > >
> > > Paul Durrant writes ("RE: [RFC PATCH 2/6] libxl: stop using
> > > libxl__xs_mkdir()
> > > for ~/control/shutdown"):
> > > > [Ian Jackson]
> > > > > Paul Durrant writes ("RE: [RFC PATCH 2/6] libxl: stop using
> > > libxl__xs_mkdir()
> > > > > for ~/control/shutdown"):
> > > > > > [Ian Jackson:]
> > > > > > > Maybe it would be easier to rename libxl__xs_mkdir to
> > > > > > > libxl__xs_mknode ?ÂÂ(It's probably too late to rename
> > > > > > > XS_MKDIR.)
> > > > > >
> > > > > > There is still the need to set the path to an empty value though,
> > > > > > which
> > > is
> > > > > not implicitly done by the XS_MKDIR.
> > > > >
> > > > > Under what circumstances would this path not contain an empty
> value
> > > > > after XS_MKDIR ?
> > > >
> > > > In this case I believe you are correct, but my feeling was that
> > > > people reading the code would be lulled into a false sense of
> > > > security that XS_MKDIR always did the right thing to initialize a
> > > > new path.
> > >
> > > I'm not sure I follow this argument.ÂÂWhat did you think of my idea
> > > of renaming libxl__xs_mkdir to libxl__xs_mknode ?
> > >
> >
> > The issue, as I said, is the initial state of the node. If you use
> > XS_MKDIR then it is not guaranteed to be empty.
> 
> Just to satisfy my curiosity, how can it be non-empty? What else could it
> possibly contain, just garbage?
> 
> Or maybe this is the behaviour of XS_MKDIR on a path/node which already
> exists?
> 

Yes, that's exactly it. I believe XS_MKDIR does guarantee to create a path 
empty, but will not clear an existing one.

  Paul

> Ian.
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