Re: [PATCH v5 06/17] virt: acrn: Introduce VM management interfaces

[Shuo A Liu]

On Thu  5.Nov'20 at  7:29:07 +0100, Greg Kroah-Hartman wrote:
> On Thu, Nov 05, 2020 at 11:10:29AM +0800, Shuo A Liu wrote:
> > On Wed  4.Nov'20 at 20:02:35 +0100, Greg Kroah-Hartman wrote:
> > > On Mon, Oct 19, 2020 at 02:17:52PM +0800, shuo.a.liu@xxxxxxxxx wrote:
> > > > --- /dev/null
> > > > +++ b/include/uapi/linux/acrn.h
> > > > @@ -0,0 +1,56 @@
> > > > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > > > +/*
> > > > + * Userspace interface for /dev/acrn_hsm - ACRN Hypervisor Service Module
> > > > + *
> > > > + * This file can be used by applications that need to communicate with the HSM
> > > > + * via the ioctl interface.
> > > > + */
> > > > +
> > > > +#ifndef _UAPI_ACRN_H
> > > > +#define _UAPI_ACRN_H
> > > > +
> > > > +#include <linux/types.h>
> > > > +
> > > > +/**
> > > > + * struct acrn_vm_creation - Info to create a User VM
> > > > + * @vmid:		User VM ID returned from the hypervisor
> > > > + * @reserved0:		Reserved
> > > > + * @vcpu_num:		Number of vCPU in the VM. Return from hypervisor.
> > > > + * @reserved1:		Reserved
> > > > + * @uuid:		UUID of the VM. Pass to hypervisor directly.
> > > > + * @vm_flag:		Flag of the VM creating. Pass to hypervisor directly.
> > > > + * @ioreq_buf:		Service VM GPA of I/O request buffer. Pass to
> > > > + *			hypervisor directly.
> > > > + * @cpu_affinity:	CPU affinity of the VM. Pass to hypervisor directly.
> > > > + * @reserved2:		Reserved
> > >
> > > Reserved and must be 0?
> >
> > Not a must.
>
> That's guaranteed to come back and bite you in the end.  

OK. I can fill them with zero before passing them to hypervisor.

> You all have read the "how to write a good api" document, right?

Is it Documentation/driver-api/ioctl.rst? Or i missed..

> > > What are they reserved for?
> > >
> > > Same for all of the reserved fields, why?
> >
> > Some reserved fields are to map layout in the hypervisor side, others
> > are for future use.
>
> ioctls should not have these, again, please read the documentation.  If
> you need something new in the future, just make a new ioctl.

OK. I will remove some reserved fields for scalability. Though i can
keep some reserved fields for alignment (and to keep same data structure
layout with the hypervisor), right?
Documentation/driver-api/ioctl.rst says that explicit reserved fields
could be used.

> > > > + */
> > > > +struct acrn_vm_creation {
> > > > +	__u16	vmid;
> > > > +	__u16	reserved0;
> > > > +	__u16	vcpu_num;
> > > > +	__u16	reserved1;
> > > > +	__u8	uuid[16];
> > >
> > > We have a userspace-visable uid structure in include/uapi/uuid.h, why
> > > not use that?
> >
> > we just pass the uuid data from user space to hypervisor. So, we can
> > remove a header dependeny with using raw data format.
>
> I do not understand this, please use the built-in kernel types we have.

OK. I will use that.

Thanks
shuo