From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f65.google.com ([209.85.215.65]:32826 "EHLO mail-lf0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757886AbcJRGGO (ORCPT ); Tue, 18 Oct 2016 02:06:14 -0400 Subject: Re: [PATCH 1/2] man2/fallocate.2: document behavior with shared blocks To: "Darrick J. Wong" References: <147675566778.12400.16090171199161180354.stgit@birch.djwong.org> Cc: mtk.manpages@gmail.com, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-xfs@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-man@vger.kernel.org From: "Michael Kerrisk (man-pages)" Message-ID: Date: Tue, 18 Oct 2016 08:06:10 +0200 MIME-Version: 1.0 In-Reply-To: <147675566778.12400.16090171199161180354.stgit@birch.djwong.org> Content-Type: text/plain; charset=utf-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: Hi Darrick, On 10/18/2016 03:54 AM, Darrick J. Wong wrote: > Add a blurb to the fallocate manpage explaining that the fallocate > command with the UNSHARE mode flag may use CoW to unshare blocks to > guarantee that a disk write won't fail with ENOSPC. Thanks! Applied. Cheers, Michael > > Signed-off-by: Darrick J. Wong > --- > man2/fallocate.2 | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > > diff --git a/man2/fallocate.2 b/man2/fallocate.2 > index 54d6340..3ed1460 100644 > --- a/man2/fallocate.2 > +++ b/man2/fallocate.2 > @@ -79,6 +79,16 @@ but the file size will not be changed even if > is greater than the file size. > Preallocating zeroed blocks beyond the end of the file in this manner > is useful for optimizing append workloads. > + > +If the > +.B FALLOC_FL_UNSHARE > +flag is specified in > +.IR mode , > +shared file data extents will be made private to the file to guarantee > +that a subsequent write will not fail due to lack of space. > +Typically, this will be done by performing a copy-on-write operation on > +all shared data in the file. > +This flag may not be supported by all filesystems. > .PP > Because allocation is done in block size chunks, > .BR fallocate () > > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/