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Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <4467.1579020509@warthog.procyon.org.uk> <00fc7691-77d5-5947-5493-5c97f262da81@gmx.com> <27181AE2-C63F-4932-A022-8B0563C72539@dilger.ca> <20200115133101.GA28583@lst.de> To: Andreas Dilger Cc: dhowells@redhat.com, Christoph Hellwig , Qu Wenruo , linux-fsdevel , Al Viro , "Theodore Y. Ts'o" , "Darrick J. Wong" , Chris Mason , Josef Bacik , David Sterba , linux-ext4 , linux-xfs , linux-btrfs , Linux Kernel Mailing List Subject: Re: Problems with determining data presence by examining extents? MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <23761.1579121702.1@warthog.procyon.org.uk> Date: Wed, 15 Jan 2020 20:55:02 +0000 Message-ID: <23762.1579121702@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org Andreas Dilger wrote: > I think what is needed here is an fadvise/ioctl that tells the filesystem > "don't allocate blocks unless actually written" for that file. Yeah - and it would probably need to find its way onto disk so that its effect is persistent and visible to out-of-kernel tools. It would also have to say that blocks of zeros shouldn't be optimised away. David