Re: [Xen-devel] [PATCH RESEND 1/4] libs, gnttab, libxc: Interface for grant copy operation

[Paulina Szubarczyk <paulinaszubarczyk@xxxxxxxxx>]

On Wed, 2016-06-01 at 12:22 +0100, David Vrabel wrote:
> On 01/06/16 08:45, Paulina Szubarczyk wrote:
> > On Tue, 2016-05-31 at 10:25 +0100, David Vrabel wrote:
> >>
> >> On 31/05/2016 05:44, Paulina Szubarczyk wrote:
> >>>
> >>>     Notification is yet not implemented.
> >>
> >> I'm not sure what you mean by "notifcation" here.
> > There is notify interface for grant map operations to communicate a
> > failure to the peer in case of teardown if the notify_port is given
> > to allow it to take care of resources. I have not checked yet how is it
> > used.
> 
> This is not relevant for grant copy, since there's no mapping that
> persists after the grant copy call.
> 
> >>> --- a/tools/libs/gnttab/gnttab_core.c
> >>> +++ b/tools/libs/gnttab/gnttab_core.c
> >>> @@ -113,6 +113,18 @@ int xengnttab_unmap(xengnttab_handle *xgt, void 
> >>> *start_address, uint32_t count)
> >>>      return osdep_gnttab_unmap(xgt, start_address, count);
> >>>  }
> >>>  
> >>> +int xengnttab_copy_grant(xengnttab_handle *xgt,
> >>> +                         uint32_t count,
> >>> +                         uint16_t *domids,
> >>> +                         uint32_t *refs,
> >>> +                         void **bufs,
> >>> +                         uint32_t *offset, 
> >>> +                         uint32_t *len,
> >>> +                         int type)
> >>
> >> This interface should match the ioctl which matches the hypercall.  In
> >> particular the ioctl (and hypercall) allows copies to and from grant
> >> references in the same call and returns a per-op status.
> >>
> > I followed the pattern of declaration for the grant map in this file
> > which as I believe is generic due to the use of it by both linux and
> > mini-os.
> 
> The library needs to expose all the functionality of the grant copy
> hypercall which includes having different ops in the call copying in
> different directions.
> 
> > The header with 'struct ioctl_gntdev_copy_segment' is linked only to the
> > linux part which issues the hypercall by gntdev, whereas mini-os does
> > not use gntdev it is not accessible at the higher level.
> 
> The library should provide its own structure that happens to look like
> the structure for the Linux ioctl.
> 
> The (future) minios implementation can use the same structure.
> 
> I think you will also find that the user of this API would prefer to
> deal with a single array of xengnttab_copy_segment_t's instead of the 5
> different arrays currently needed.

Ok, it will be changed.

> >> Using the same structure in libxc would also allow you to a) remove the
> >> memory allocations; and b) avoid having to fill in a different structure.
> >>
> >> I would suggest:
> >>
> >> int xengnttab_copy_grant(xengnttab_handle *xgt,
> >>    unsigned int count,
> >>    xengnttab_copy_segment_t *segs);
> >>
> >> With:
> >>
> >> typedef struct ioctl_gntdev_copy_segment xengnttab_copy_segment_t;
> >>
> >> You should put the required struct ioctl_gntdev_grant_copy on the stack
> >> since it is small.
> 
> David
> 
Paulina



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