linux-kernel - Re: [PATCH 05/10] PCI/P2PDMA: Export pci_p2pdma_map

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Message-ID: <20250729075230.GB23823@lst.de>
Date: Tue, 29 Jul 2025 09:52:30 +0200
From: Christoph Hellwig <hch@....de>
To: Leon Romanovsky <leon@...nel.org>
Cc: Christoph Hellwig <hch@....de>,
	Alex Williamson <alex.williamson@...hat.com>,
	Jason Gunthorpe <jgg@...dia.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Christian König <christian.koenig@....com>,
	dri-devel@...ts.freedesktop.org, iommu@...ts.linux.dev,
	Jens Axboe <axboe@...nel.dk>,
	Jérôme Glisse <jglisse@...hat.com>,
	Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
	linaro-mm-sig@...ts.linaro.org, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	linux-mm@...ck.org, linux-pci@...r.kernel.org,
	Logan Gunthorpe <logang@...tatee.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Vivek Kasireddy <vivek.kasireddy@...el.com>,
	Will Deacon <will@...nel.org>
Subject: Re: [PATCH 05/10] PCI/P2PDMA: Export pci_p2pdma_map_type() function

On Thu, Jul 24, 2025 at 11:13:21AM +0300, Leon Romanovsky wrote:
> On Thu, Jul 24, 2025 at 10:03:13AM +0200, Christoph Hellwig wrote:
> > On Wed, Jul 23, 2025 at 04:00:06PM +0300, Leon Romanovsky wrote:
> > > From: Leon Romanovsky <leonro@...dia.com>
> > > 
> > > Export the pci_p2pdma_map_type() function to allow external modules
> > > and subsystems to determine the appropriate mapping type for P2PDMA
> > > transfers between a provider and target device.
> > 
> > External modules have no business doing this.
> 
> VFIO PCI code is built as module. There is no way to access PCI p2p code
> without exporting functions in it.

We never ever export anything for "external" modules, and you really
should know that.