Re: [PATCH V1 02/16] xen/ioreq: Make x86's IOREQ feature common

[Jan Beulich <jbeulich@xxxxxxxx>]

On 21.09.2020 21:02, Oleksandr wrote:
> On 14.09.20 17:17, Jan Beulich wrote:
>> On 10.09.2020 22:21, Oleksandr Tyshchenko wrote:
>>> --- /dev/null
>>> +++ b/xen/include/xen/ioreq.h
>>> @@ -0,0 +1,82 @@
>>> +/*
>>> + * ioreq.h: Hardware virtual machine assist interface definitions.
>>> + *
>>> + * Copyright (c) 2016 Citrix Systems Inc.
>>> + *
>>> + * This program is free software; you can redistribute it and/or modify it
>>> + * under the terms and conditions of the GNU General Public License,
>>> + * version 2, as published by the Free Software Foundation.
>>> + *
>>> + * This program is distributed in the hope it will be useful, but WITHOUT
>>> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
>>> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License 
>>> for
>>> + * more details.
>>> + *
>>> + * You should have received a copy of the GNU General Public License along 
>>> with
>>> + * this program; If not, see <http://www.gnu.org/licenses/>.
>>> + */
>>> +
>>> +#ifndef __IOREQ_H__
>>> +#define __IOREQ_H__
>> __XEN_IOREQ_H__ please.
> 
> ok
> 
> 
>>
>>> +#include <xen/sched.h>
>>> +
>>> +#include <asm/hvm/ioreq.h>
>> Is this include really needed here (i.e. by the code further down in
>> the file, and hence by everyone including this header), or rather
>> just in a few specific .c files?
> I think, just in few specific .c files. Which are x86/hvm/ioreq.c and 
> common/ioreq.c now and several other files later on (x86/hvm/dm.c, 
> arm/io.c, etc)
> Shall I include that header in these files instead?

Yes please, and please take this as a common guideline. While
private headers are often used to include things needed by all
of the (typically few) users of the header, non-private ones
shouldn't create unnecessary dependencies on other headers. As
you've said further up - you did run into hard to resolve
header dependencies yourself, and the practice of including
headers without strict need is one of the reasons of such
problems.

>>> +#define GET_IOREQ_SERVER(d, id) \
>>> +    (d)->arch.hvm.ioreq_server.server[id]
>> arch.hvm.* feels like a layering violation when used in this header.
> Got it. The only reason why GET_IOREQ_SERVER is here is inline 
> get_ioreq_server(). I will make it non-inline and move both to 
> common/ioreq.c.

Which won't make the layering violation go away. It's still
common rather than per-arch code then. As suggested elsewhere,
I think the whole ioreq_server struct wants to move into
struct domain itself, perhaps inside a new #ifdef (iirc one of
the patches introduces a suitable Kconfig option). This goes
alongside my suggestion to drop the "hvm" prefixes and infixes
from involved function names.

Jan