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[142.162.113.129]) by smtp.gmail.com with ESMTPSA id f10-20020a05620a280a00b006a69d7f390csm27745242qkp.103.2022.07.05.06.51.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 Jul 2022 06:51:02 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1o8ixC-006VQ4-6E; Tue, 05 Jul 2022 10:51:02 -0300 Date: Tue, 5 Jul 2022 10:51:02 -0300 From: Jason Gunthorpe To: Christoph Hellwig Cc: Logan Gunthorpe , linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, iommu@lists.linux-foundation.org, Stephen Bates , Dan Williams , Christian =?utf-8?B?S8O2bmln?= , John Hubbard , Don Dutile , Matthew Wilcox , Daniel Vetter , Minturn Dave B , Jason Ekstrand , Dave Hansen , Xiong Jianxin , Bjorn Helgaas , Ira Weiny , Robin Murphy , Martin Oliveira , Chaitanya Kulkarni , Ralph Campbell , Bjorn Helgaas Subject: Re: [PATCH v7 20/21] PCI/P2PDMA: Introduce pci_mmap_p2pmem() Message-ID: <20220705135102.GE23621@ziepe.ca> References: <20220615161233.17527-1-logang@deltatee.com> <20220615161233.17527-21-logang@deltatee.com> <20220629064854.GD17576@lst.de> <99242789-66a6-bbd2-b56a-e47891f4522e@deltatee.com> <20220629175906.GU23621@ziepe.ca> <20220705075108.GB17451@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220705075108.GB17451@lst.de> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1657029064; a=rsa-sha256; cv=none; b=EOWRJYjihxwiNsuvO/SU1/BUGG8uc+zUJdlkY0wF11WmFF3ctgFvYDgMlWryj+37bf+nA3 SgBvg36Kl+jnaH7bYMO4Xdymj7dn9wh7rcUXLnhJEcoIVIX7L+UVWRB2+bN8FKAiFEzmUX 7TFu9p+Wh8C85cy2ceiAWD7hM/N0gEA= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=ziepe.ca header.s=google header.b=cDfN+bQc; dmarc=none; spf=pass (imf23.hostedemail.com: domain of jgg@ziepe.ca designates 209.85.160.173 as permitted sender) smtp.mailfrom=jgg@ziepe.ca ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1657029064; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=aXXqCO4eYEW7ihl1nkLRPlC9zfL+9NshKktoq8vfUqo=; b=rogYwrCgrYdxTcwX93BROol/R/sdySZu9JUU+lm1pgunkWQCpLnWsDvMZbktsiIOnUAbb1 UVEWmuQNdl/xeKyTIjfftGkRMJLNiVoz29nR12+cd/bCtcPn1warQV1q5EWWq1XSZ0k8vu 03bgBR+r2hmyusc3UEZG8g4uCC9cOL4= Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=ziepe.ca header.s=google header.b=cDfN+bQc; dmarc=none; spf=pass (imf23.hostedemail.com: domain of jgg@ziepe.ca designates 209.85.160.173 as permitted sender) smtp.mailfrom=jgg@ziepe.ca X-Rspam-User: X-Stat-Signature: 4yrjpwqeagiugurb7mxbky6qo5egrz1q X-Rspamd-Queue-Id: 80355140011 X-Rspamd-Server: rspam04 X-HE-Tag: 1657029064-863240 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jul 05, 2022 at 09:51:08AM +0200, Christoph Hellwig wrote: > But what also really matters here: I don't want every user that > wants to be able to mmap a character device to do all this work. > The layering is simply wrong, it needs some character device > based helpers, not be open code everywhere. I think alot (all?) cases would be happy if the inode was 1:1 with the cdev struct device. I suppose the cdev code would still have to create pseudo fs, but at least that is hidden. > In fact I'm not even sure this should be a character device, it seems > to fit it way better with the PCI sysfs hierchacy, just like how we > map MMIO resources, which these are anyway. And once it is on sysfs > we do have a uniqueue inode and need none of the pseudofs stuff, and > don't need all the glue code in nvme either. Shouldn't there be an allocator here? It feels a bit weird that the entire CMB is given to a single process, it is a sharable resource, isn't it? Jason