Re: [Qemu-devel] [PATCH V6 4/5] pvrdma: initial implementation

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 9 Jan 2018 13:08:33 +0200
Yuval Shaia <yuval.shaia@oracle.com> wrote:

> On Tue, Jan 09, 2018 at 11:39:11AM +0100, Cornelia Huck wrote:
> > On Sun,  7 Jan 2018 14:32:23 +0200
> > Marcel Apfelbaum <marcel@redhat.com> wrote:

> > > diff --git a/hw/rdma/vmw/pvrdma_dev_api.h b/hw/rdma/vmw/pvrdma_dev_api.h
> > > new file mode 100644
> > > index 0000000000..bf1986a976
> > > --- /dev/null
> > > +++ b/hw/rdma/vmw/pvrdma_dev_api.h
> > > @@ -0,0 +1,602 @@
> > > +/*
> > > + * QEMU VMWARE paravirtual RDMA device definitions
> > > + *
> > > + * Copyright (C) 2018 Oracle
> > > + * Copyright (C) 2018 Red Hat Inc
> > > + *
> > > + * Authors:
> > > + *     Yuval Shaia <yuval.shaia@oracle.com>
> > > + *     Marcel Apfelbaum <marcel@redhat.com>
> > > + *
> > > + * This work is licensed under the terms of the GNU GPL, version 2.
> > > + * See the COPYING file in the top-level directory.
> > > + *
> > > + */
> > > +
> > > +#ifndef PVRDMA_DEV_API_H
> > > +#define PVRDMA_DEV_API_H
> > > +
> > > +/*
> > > + * Following is an interface definition for PVRDMA device as provided by
> > > + * VMWARE.
> > > + * See original copyright from Linux kernel v4.14.5 header file
> > > + * drivers/infiniband/hw/vmw_pvrdma/pvrdma_dev_api.h  
> > 
> > Could that file be exported as UAPI in the kernel and added to the
> > linux-headers script?  
> 
> We took this approach as apposed to kernel-headers with the following on
> our mind:
> (1) This is the convention used in vmxnet3.
> (2) vmw_pvrdma was introduced only lately, taking the kernel-headers
> approach will force specific kernel on a host in order to compile QEMU.

qemu will get the kernel headers once from the upstream kernel and then
will be able to be built everywhere.

> (3) To support VMWare's pvrdma device we took a snapshot of existing
> driver/device settings and breezed there. This is driver/device API and we
> can't allow our self to chase VMWare's tail whenever they are changing the
> API. Just consider a case where they will change for example the ARM bit.

But as want to enable the existing device driver, you'll want to be
able to produce a compatible device anyway, don't you? Also, wouldn't
VMWare break older kernels if they suddenly changed the api?

[Also, is there a canonical reference for this API?]

> 
> Just IMHO.
> 
> > 
> > (...)
> >   
> > > diff --git a/hw/rdma/vmw/pvrdma_ib_verbs.h b/hw/rdma/vmw/pvrdma_ib_verbs.h
> > > new file mode 100644
> > > index 0000000000..cf1430024b
> > > --- /dev/null
> > > +++ b/hw/rdma/vmw/pvrdma_ib_verbs.h
> > > @@ -0,0 +1,433 @@
> > > +/*
> > > + * QEMU VMWARE paravirtual RDMA device definitions
> > > + *
> > > + * Copyright (C) 2018 Oracle
> > > + * Copyright (C) 2018 Red Hat Inc
> > > + *
> > > + * Authors:
> > > + *     Yuval Shaia <yuval.shaia@oracle.com>
> > > + *     Marcel Apfelbaum <marcel@redhat.com>
> > > + *
> > > + * This work is licensed under the terms of the GNU GPL, version 2.
> > > + * See the COPYING file in the top-level directory.
> > > + *
> > > + */
> > > +
> > > +#ifndef PVRDMA_IB_VERBS_H
> > > +#define PVRDMA_IB_VERBS_H
> > > +
> > > +/*
> > > + * VMWARE headers we got from Linux kernel do not fully comply QEMU coding
> > > + * standards in sense of types and defines used.
> > > + * Since we didn't want to change VMWARE code, following set of typedefs
> > > + * and defines needed to compile these headers with QEMU introduced.
> > > + */
> > > +
> > > +#define u8     uint8_t
> > > +#define u16    unsigned short
> > > +#define u32    uint32_t
> > > +#define u64    uint64_t  
> > 
> > I think the headers update already takes care of some conversions.
> > Otherwise, same comment as for the header above.  
> 
> Sorry, i'm not following, can you elaborate on that?

There's some post processing done by the headers update. But I think
you'd need to use __u8 and friends for an exported header anyway.

> 
> >   
> > > +
> > > +/*
> > > + * Following is an interface definition for PVRDMA device as provided by
> > > + * VMWARE.
> > > + * See original copyright from Linux kernel v4.14.5 header file
> > > + * drivers/infiniband/hw/vmw_pvrdma/pvrdma_verbs.h
> > > + */  
> > 
> > (...)
> >   
> > > diff --git a/hw/rdma/vmw/vmw_pvrdma-abi.h b/hw/rdma/vmw/vmw_pvrdma-abi.h
> > > new file mode 100644
> > > index 0000000000..8cfb9d7745
> > > --- /dev/null
> > > +++ b/hw/rdma/vmw/vmw_pvrdma-abi.h
> > > @@ -0,0 +1,311 @@
> > > +/*
> > > + * QEMU VMWARE paravirtual RDMA device definitions
> > > + *
> > > + * Copyright (C) 2018 Oracle
> > > + * Copyright (C) 2018 Red Hat Inc
> > > + *
> > > + * Authors:
> > > + *     Yuval Shaia <yuval.shaia@oracle.com>
> > > + *     Marcel Apfelbaum <marcel@redhat.com>
> > > + *
> > > + * This work is licensed under the terms of the GNU GPL, version 2.
> > > + * See the COPYING file in the top-level directory.
> > > + *
> > > + */
> > > +
> > > +#ifndef VMW_PVRDMA_ABI_H
> > > +#define VMW_PVRDMA_ABI_H
> > > +
> > > +/*
> > > + * Following is an interface definition for PVRDMA device as provided by
> > > + * VMWARE.
> > > + * See original copyright from Linux kernel v4.14.5 header file
> > > + * include/uapi/rdma/vmw_pvrdma-abi.h
> > > + */  
> > 
> > This one is already exported.  
> 
> Same argument as above.

Well, I sure hope VMWare is not planning to change an exported ABI in
an incompatible way...