Re: [PATCH v2 3/3] xen-hvm: try to use xenforeignmemory_map_resource() to map ioreq pages

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Anthony PERARD [mailto:anthony.perard@citrix.com]
> Sent: 15 May 2018 17:17
> To: Paul Durrant <Paul.Durrant@citrix.com>
> Cc: qemu-devel@nongnu.org; xen-devel@lists.xenproject.org; Stefano
> Stabellini <sstabellini@kernel.org>
> Subject: Re: [PATCH v2 3/3] xen-hvm: try to use
> xenforeignmemory_map_resource() to map ioreq pages
> 
> On Tue, May 15, 2018 at 04:45:25PM +0100, Paul Durrant wrote:
> > > > diff --git a/include/hw/xen/xen_common.h
> > > b/include/hw/xen/xen_common.h
> > > > index 5f1402b494..d925751040 100644
> > > > --- a/include/hw/xen/xen_common.h
> > > > +++ b/include/hw/xen/xen_common.h
> > > > @@ -119,6 +119,20 @@ static inline int
> > > xendevicemodel_pin_memory_cacheattr(
> > > >      return xc_domain_pin_memory_cacheattr(xen_xc, domid, start,
> end,
> > > type);
> > > >  }
> > > >
> > > > +typedef void xenforeignmemory_resource_handle;
> > > > +
> > > > +#define XENMEM_resource_ioreq_server_frame_bufioreq 0
> > > > +#define XENMEM_resource_ioreq_server_frame_ioreq(n) (1 + (n))
> > > > +
> > > > +static inline xenforeignmemory_resource_handle
> > > *xenforeignmemory_map_resource(
> > > > +    xenforeignmemory_handle *fmem, domid_t domid, unsigned int
> type,
> > > > +    unsigned int id, unsigned long frame, unsigned long nr_frames,
> > > > +    void **paddr, int prot, int flags)
> > > > +{
> > > > +    errno = EOPNOTSUPP;
> > >
> > > I think ENOSYS would be better. EOPNOTSUPP seems to be for sockets.
> > >
> >
> > No, EOPNOTSUPP is more general than that and is convention for
> unimplemented API operations elsewhere. ENOSYS is supposed to strictly
> mean 'system call not implemented' but we use it for hypercalls in Xen,
> leading to occasional fun with Linux checkpatch.pl.
> 
> In man errno, I have:
> ENOTSUP         Operation not supported (POSIX.1-2001)
> EOPNOTSUPP      Operation not supported on socket (POSIX.1-2001).
> ENOSYS          Function not implemented (POSIX.1-2001).
> 
> But I guess any of these would work.

My reference is the non-Linux definitions in tools/libs/foreignmemory/private.h in the Xen tree. The one for xenforeignmemory_map_resource() is as follows:

static inline int osdep_xenforeignmemory_map_resource(
    xenforeignmemory_handle *fmem, xenforeignmemory_resource_handle *fres)
{
    errno = EOPNOTSUPP;
    return -1;
}

So I'll stick with EOPNOTSUPP.

Cheers,

  Paul

> 
> --
> Anthony PERARD

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