linux-kernel - Re: [PATCH v7 20/21] PCI/P2PDMA: Introduce pci_mmap

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Date:   Wed, 6 Jul 2022 15:30:30 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christoph Hellwig <hch@....de>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-block@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-mm@...ck.org,
        iommu@...ts.linux-foundation.org,
        Stephen Bates <sbates@...thlin.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Christian König <christian.koenig@....com>,
        John Hubbard <jhubbard@...dia.com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        Martin Oliveira <martin.oliveira@...eticom.com>,
        Chaitanya Kulkarni <ckulkarnilinux@...il.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v7 20/21] PCI/P2PDMA: Introduce pci_mmap_p2pmem()



On 2022-07-06 01:04, Greg Kroah-Hartman wrote:
> On Wed, Jul 06, 2022 at 08:51:27AM +0200, Christoph Hellwig wrote:
>> On Tue, Jul 05, 2022 at 12:16:45PM -0600, Logan Gunthorpe wrote:
>>> The current version does it through a char device, but that requires
>>> creating a simple_fs and anon_inode for teardown on driver removal, plus
>>> a bunch of hooks through the driver that exposes it (NVMe, in this case)
>>> to set this all up.
>>>
>>> Christoph is suggesting a sysfs interface which could potentially avoid
>>> the anon_inode and all of the extra hooks. It has some significant
>>> benefits and maybe some small downsides, but I wouldn't describe it as
>>> horrid.
>>
>> Yeah, I don't think is is horrible, it fits in with the resource files
>> for the BARs, and solves a lot of problems.  Greg, can you explain
>> what would be so bad about it?
> 
> As you mention, you will have to pass different things down into sysfs
> in order for that to be possible.  If it matches the resource files like
> we currently have today, that might not be that bad, but it still feels
> odd to me.  Let's see an implementation and a Documentation/ABI/ entry
> first though.

I'll work something up in the coming weeks.

Thanks,

Logan