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

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Message-ID: <ZpC8zalggIyzdTFQ@yzhao56-desk>
Date: Fri, 12 Jul 2024 13:19:09 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Yi Liu <yi.l.liu@...el.com>, "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 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?