Re: [Xen-devel] [v4][PATCH 3/9] tools:libxc: introduce hypercall for xc_reserved_device_memory_map

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

On 2014/8/22 18:55, Andrew Cooper wrote:
> On 22/08/14 11:09, Tiejun Chen wrote:
> > We will introduce that hypercall xc_reserved_device_memory_map
> > to libxc.
> >
> > Signed-off-by: Tiejun Chen <tiejun.chen@xxxxxxxxx>
> > ---
> >   tools/libxc/xc_domain.c | 29 +++++++++++++++++++++++++++++
> >   tools/libxc/xenctrl.h   |  4 ++++
> >   2 files changed, 33 insertions(+)
> >
> > diff --git a/tools/libxc/xc_domain.c b/tools/libxc/xc_domain.c
> > index c67ac9a..08dc16f 100644
> > --- a/tools/libxc/xc_domain.c
> > +++ b/tools/libxc/xc_domain.c
> > @@ -649,6 +649,35 @@ int xc_domain_set_memory_map(xc_interface *xch,
> >
> >       return rc;
> >   }
> > +
> > +int xc_reserved_device_memory_map(xc_interface *xch,
> > +                                  struct xen_reserved_device_memory entries[],
> > +                                  uint32_t max_entries)
> > +{
> > +    int rc;
> > +    struct xen_reserved_device_memory_map memmap = {
> > +        .nr_entries = max_entries
> > +    };
> > +    DECLARE_HYPERCALL_BOUNCE(entries,
> > +                             sizeof(struct xen_reserved_device_memory) *
> > +                             max_entries, XC_HYPERCALL_BUFFER_BOUNCE_OUT);
> > +
> > +    if ( xc_hypercall_bounce_pre(xch, entries) )
> > +        return -1;
> > +
> > +    set_xen_guest_handle(memmap.buffer, entries);
> > +
> > +    rc = do_memory_op(xch, XENMEM_reserved_device_memory_map,
> > +                      &memmap, sizeof(memmap));
> > +
> > +    xc_hypercall_bounce_post(xch, entries);
> > +
> > +    if ( errno == ENOBUFS )
> > +        return memmap.nr_entries;
> > +
> > +    return rc ? -errno : memmap.nr_entries;
> So how does the caller distinguish between "xen filled in N entries" and
> "xen said you need N entries for all the information" ?
Thanks for your reminder, I will add something to check this point.

I think the caller can compare that number of entries as that input 
parameter with the return value. If equal, this should be in case of 
"xen filled in N entries". If not, this is in case of "xen said you need 
N entries for all the information".
Thanks
Tiejun

> ~Andrew
>
> > +}
> > +
> >   int xc_get_machine_memory_map(xc_interface *xch,
> >                                 struct e820entry entries[],
> >                                 uint32_t max_entries)
> > diff --git a/tools/libxc/xenctrl.h b/tools/libxc/xenctrl.h
> > index 1c5d0db..1cc7852 100644
> > --- a/tools/libxc/xenctrl.h
> > +++ b/tools/libxc/xenctrl.h
> > @@ -1270,6 +1270,10 @@ int xc_domain_set_memory_map(xc_interface *xch,
> >   int xc_get_machine_memory_map(xc_interface *xch,
> >                                 struct e820entry entries[],
> >                                 uint32_t max_entries);
> > +
> > +int xc_reserved_device_memory_map(xc_interface *xch,
> > +                                  struct xen_reserved_device_memory entries[],
> > +                                  uint32_t max_entries);
> >   #endif
> >   int xc_domain_set_time_offset(xc_interface *xch,
> >                                 uint32_t domid,
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