linux-kernel - Re: [PATCH] vfio: Reuse file f

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Message-ID: <46496896-0dda-4d2b-8092-021d33e4862a@intel.com>
Date: Fri, 12 Jul 2024 14:14:08 +0800
From: Yi Liu <yi.l.liu@...el.com>
To: Yan Zhao <yan.y.zhao@...el.com>, Jason Gunthorpe <jgg@...dia.com>
CC: "Tian, Kevin" <kevin.tian@...el.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "alex.williamson@...hat.com"
	<alex.williamson@...hat.com>, "peterx@...hat.com" <peterx@...hat.com>,
	"ajones@...tanamicro.com" <ajones@...tanamicro.com>
Subject: Re: [PATCH] vfio: Reuse file f_inode as vfio device inode

On 2024/7/12 13:19, Yan Zhao wrote:
> On Wed, Jul 10, 2024 at 11:40:44AM -0300, Jason Gunthorpe wrote:
>> On Mon, Jul 01, 2024 at 01:48:07PM +0800, Yan Zhao wrote:
>>
>>> No, I don't have such a need.
>>> I just find it's confusing to say "Only the group path allows the device to be
>>> opened multiple times. The device cdev path doesn't have a secure way for it",
>>> since it's still doable to achieve the same "secure" level in cdev path and the
>>> group path is not that "secure" :)
>>
>> It is more that the group path had an API that allowed for multiple
>> FDs without an actual need to ever use that. You can always make more
>> FDs with dup.
>>
>> There is no reason for this functionality, we just have to keep it
>> working as a matter of uABI compatability and we are being more strict
>> in the new APIs.
> Thanks for clarification.
> Regarding to uABI compatability, even after being more strict and returning
> error when opening the second FD in group path, the uABI compatability is still
> maintained? e.g.
> QEMU would correctly reports "Verify all devices in group xxx are bound to
> vfio-<bus> or pci-stub and not already in use" in that case.
> Given there's no actual users, could we also remove the support of multiple FDs
> in group path to simplify code?

QEMU is not the only user of vfio. DPDK or other applications may have
usage for multi-fds.

-- 
Regards,
Yi Liu