From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f179.google.com (mail-pl1-f179.google.com [209.85.214.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E52842C8B for ; Thu, 4 Nov 2021 18:10:30 +0000 (UTC) Received: by mail-pl1-f179.google.com with SMTP id b13so8626674plg.2 for ; Thu, 04 Nov 2021 11:10:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20210112.gappssmtp.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=7mdrEIaynFJhMAYVbY2RCFSQ3xBs/5manpadoyeA8Jg=; b=0YEcomScst+1AzYcEtB+P3/DmeUM77501UDi4utLMr5xdKJlnd8UevBd12j9FnZ3vM pfReEE9Mys+ZVEwliSTF7urxA8Wo0+Hi1QGvdNyLT71G18SgBjzWHXiXc01F/GMcT30o 4sj59niVU83geSVU+jTxOcRmF241hREk19CsoBH8kxr2RQdc6rHN1RFVCxVTxuFK53C5 ubx4NqJpME+C1zDILd+MfHjSjbqUFn2nDpjUaVUu+wM8te1yVWJyRStj28nUJ7WDbMUk H2RDjE1nkFNI+5JNwfhWiSHo+ZLBnVukougjDJ/S9PImKe7sfLSLlzrr4uAIBYjBE48z eouQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=7mdrEIaynFJhMAYVbY2RCFSQ3xBs/5manpadoyeA8Jg=; b=35W3CdZHod4IM2fUt1+c3ho57EKwwVG2f8XQn5yLZLFfb89+2FYan+UFGsvvta43Sn 5Z9u+aOMO/ifz2E3vYAobF6Y7DQAOxh5m/g4m3egJ7kSA/1mASikmhcMIwTbFkUslYc1 2b/STHs6/heEmtnlLB6o9lLns8tYZjbjIXOZHJW1akSDPpHnhMZLG9i8Qgqcp0elc9Ub CgGYtJggLY3zCiNloNqOCAm3xR/T57mkvrVyDcoSjNzJYtOkODZv5hTUfqxaa09EZ2bq XGYFQB1cZOyLiZ6UTFCWiAUUVGiZMNQ/YlMTfmshXc8E9vXnN7uNwSErmt6FJDy+SWUR 8qXg== X-Gm-Message-State: AOAM533LJc6RaEyi5iFIetOythNv65O0+XO1VshJVSI80x/pviX2CMtd o/WAP6rBxi+WvzG6StwzK9WylvFid7d5+SyJjETqXA== X-Google-Smtp-Source: ABdhPJxpE7179nYWnBAffbsem/btoh3olrocKEPy5McMuIBWtGLmZ02iwXqFLVvSNceMnE3VXVk1wLsDAvNCq2GAmrQ= X-Received: by 2002:a17:902:b697:b0:141:c7aa:e10f with SMTP id c23-20020a170902b69700b00141c7aae10fmr33445935pls.18.1636049430346; Thu, 04 Nov 2021 11:10:30 -0700 (PDT) Precedence: bulk X-Mailing-List: nvdimm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20211018044054.1779424-1-hch@lst.de> <21ff4333-e567-2819-3ae0-6a2e83ec7ce6@sandeen.net> <20211104081740.GA23111@lst.de> <20211104173417.GJ2237511@magnolia> <20211104173559.GB31740@lst.de> In-Reply-To: <20211104173559.GB31740@lst.de> From: Dan Williams Date: Thu, 4 Nov 2021 11:10:19 -0700 Message-ID: Subject: Re: futher decouple DAX from block devices To: Christoph Hellwig Cc: "Darrick J. Wong" , Eric Sandeen , Mike Snitzer , Ira Weiny , device-mapper development , linux-xfs , Linux NVDIMM , linux-s390 , linux-fsdevel , linux-erofs@lists.ozlabs.org, linux-ext4 , virtualization@lists.linux-foundation.org Content-Type: text/plain; charset="UTF-8" On Thu, Nov 4, 2021 at 10:36 AM Christoph Hellwig wrote: > > On Thu, Nov 04, 2021 at 10:34:17AM -0700, Darrick J. Wong wrote: > > /me wonders, are block devices going away? Will mkfs.xfs have to learn > > how to talk to certain chardevs? I guess jffs2 and others already do > > that kind of thing... but I suppose I can wait for the real draft to > > show up to ramble further. ;) > > Right now I've mostly been looking into the kernel side. An no, I > do not expect /dev/pmem* to go away as you'll still need it for a > not DAX aware file system and/or application (such as mkfs initially). > > But yes, just pointing mkfs to the chardev should be doable with very > little work. We can point it to a regular file after all. Note that I've avoided implementing read/write fops for dax devices partly out of concern for not wanting to figure out shared-mmap vs write coherence issues, but also because of a bet with Dave Hansen that device-dax not grow features like what happened to hugetlbfs. So it would seem mkfs would need to switch to mmap I/O, or bite the bullet and implement read/write fops in the driver.