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

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Message-ID: <20201105073545.GD17702@shuo-intel.sh.intel.com>
Date:   Thu, 5 Nov 2020 15:35:45 +0800
From:   Shuo A Liu <shuo.a.liu@...el.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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  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@...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.  

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