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

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Date:   Thu, 5 Nov 2020 07:29:07 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Shuo A Liu <shuo.a.liu@...el.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Yu Wang <yu1.wang@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>
Subject: Re: [PATCH v5 06/17] virt: acrn: Introduce VM management interfaces

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@...el.com 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.  You all have
read the "how to write a good api" document, right?

> > 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.

> > > + */
> > > +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.

thanks,

greg k-h