Re: [Xen-devel] [PATCH v6 07/11] xen: introduce rangeset_consume_ranges

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Sep 21, 2017 at 03:42:49PM +0100, Roger Pau Monné wrote:
> On Thu, Sep 21, 2017 at 02:53:54PM +0100, Wei Liu wrote:
> > On Tue, Sep 19, 2017 at 04:29:32PM +0100, Roger Pau Monne wrote:
> > > This function allows to iterate over a rangeset while removing the
> > > processed regions.
> > > 
> > > It will be used by the following patches in order to store memory
> > > regions in rangesets, and remove them while iterating.
> > > 
> > > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > > ---
> > > Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> > > Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> > > Cc: Jan Beulich <jbeulich@xxxxxxxx>
> > > Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > > Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > > Cc: Tim Deegan <tim@xxxxxxx>
> > > Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> > > ---
> > > Changes since v5:
> > >  - New in this version.
> > > ---
> > >  xen/common/rangeset.c      | 28 ++++++++++++++++++++++++++++
> > >  xen/include/xen/rangeset.h |  4 ++++
> > >  2 files changed, 32 insertions(+)
> > > 
> > > diff --git a/xen/common/rangeset.c b/xen/common/rangeset.c
> > > index 6c6293c15c..fd4a6b3384 100644
> > > --- a/xen/common/rangeset.c
> > > +++ b/xen/common/rangeset.c
> > > @@ -298,6 +298,34 @@ int rangeset_report_ranges(
> > >      return rc;
> > >  }
> > 
> > I think you need to document the behaviour of this new function due to
> > its destructive nature.
> > 
> > Something like:
> > 
> > Iterate through the range within a range set. Call cb on each range
> > provided. Bail on first error. Destroy the range processed when cb
> > has consumed the whole range.
> 
> OK, I thought that the 'consume' in the name was enough, but now that
> you have written the comment I certainly don't mind adding it ;).
> 
> > Though without reading further I don't know why cb will only consume
> > part of the range but not all of it all the time.
> 
> I guess you have to look at the next patch and it's usage. This will
> be used to store all the MMIO areas that need to be mapped into a
> domain p2m.
> 
> Some of the ranges might be very big (BARs from gfx cards for
> example), and might require preemption in order to map them, hence the
> emulated PCI code needs a way to store it's progress, and that's done
> by partially consuming a range.
> 

Ah, so the goal is indeed to consume all the ranges within the rangeset.
This makes more sense now.

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