From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:53782 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932732AbbDJN20 (ORCPT ); Fri, 10 Apr 2015 09:28:26 -0400 From: David Howells In-Reply-To: <20150409235234.GJ13731@dastard> References: <20150409235234.GJ13731@dastard> <20150409174916.5a2efef5@notabene.brown> <29536.1428571388@warthog.procyon.org.uk> To: Dave Chinner Cc: dhowells@redhat.com, NeilBrown , linux-btrfs@vger.kernel.org, linux-cachefs@redhat.com, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH/RFC] fscache/cachefiles versus btrfs MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Date: Fri, 10 Apr 2015 14:28:16 +0100 Message-ID: <9282.1428672496@warthog.procyon.org.uk> Sender: linux-btrfs-owner@vger.kernel.org List-ID: Dave Chinner wrote: > SEEK_HOLE/SEEK_DATA is what you want, as they are page cache > coherent, not extent based operations. And, really if you need it to > really be able to find real holes, then a superblock flag might be a > better way of marking filesystems with the required capability. Actually, I wonder if what I want is a kernel_read() that returns ENODATA upon encountering a hole at the beginning of the area to be read. Of course, what I really, really want is asynchronous, direct read and write within the kernel, where the read will notify you of any holes, but will read all the data it can around those holes. David