Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932341AbVJaJtO (ORCPT ); Mon, 31 Oct 2005 04:49:14 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932363AbVJaJtO (ORCPT ); Mon, 31 Oct 2005 04:49:14 -0500 Received: from ppsw-7.csi.cam.ac.uk ([131.111.8.137]:8068 "EHLO ppsw-7.csi.cam.ac.uk") by vger.kernel.org with ESMTP id S932341AbVJaJtN (ORCPT ); Mon, 31 Oct 2005 04:49:13 -0500 X-Cam-SpamDetails: Not scanned X-Cam-AntiVirus: No virus found X-Cam-ScannerInfo: http://www.cam.ac.uk/cs/email/scanner/ Subject: Re: [PATCH against 2.6.14] truncate() or ftruncate shouldn't change mtime if size doesn't change. From: Anton Altaparmakov To: Andrew Morton Cc: NeilBrown , linux-kernel@vger.kernel.org In-Reply-To: <20051030234837.36c7a249.akpm@osdl.org> References: <20051031173358.9566.patches@notabene> <1051031063444.9586@suse.de> <20051030234837.36c7a249.akpm@osdl.org> Content-Type: text/plain Organization: Computing Service, University of Cambridge, UK Date: Mon, 31 Oct 2005 09:48:44 +0000 Message-Id: <1130752124.7504.13.camel@imp.csi.cam.ac.uk> Mime-Version: 1.0 X-Mailer: Evolution 2.4.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3923 Lines: 113 Hi, On Sun, 2005-10-30 at 23:48 -0800, Andrew Morton wrote: > NeilBrown wrote: > > According to Posix and SUS, truncate(2) and ftruncate(2) only update > > ctime and mtime if the size actually changes. Linux doesn't currently > > obey this. > > > > There is no need to test the size under i_sem, as loosing any race > > will not make a noticable different the mtime or ctime. > > Well if there's a race then the file may end up not being truncated after > this patch is applied. But that could have happened anwyay, so I don't see > a need for i_sem synchronisation either. > > > (According to SUS, truncate and ftruncate 'may' clear setuid/setgid > > as well, currently we don't. Should we? > > ) > > > > > > Signed-off-by: Neil Brown > > > > ### Diffstat output > > ./fs/open.c | 6 ++++-- > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > diff ./fs/open.c~current~ ./fs/open.c > > --- ./fs/open.c~current~ 2005-10-31 16:22:44.000000000 +1100 > > +++ ./fs/open.c 2005-10-31 16:22:44.000000000 +1100 > > @@ -260,7 +260,8 @@ static inline long do_sys_truncate(const > > goto dput_and_out; > > > > error = locks_verify_truncate(inode, NULL, length); > > - if (!error) { > > + if (!error && > > + length != i_size_read(dentry->d_inode)) { > > Odd code layout? > > > DQUOT_INIT(inode); > > error = do_truncate(nd.dentry, length); > > } > > @@ -313,7 +314,8 @@ static inline long do_sys_ftruncate(unsi > > goto out_putf; > > > > error = locks_verify_truncate(inode, file, length); > > - if (!error) > > + if (!error && > > + length != i_size_read(dentry->d_inode)) > > error = do_truncate(dentry, length); > > out_putf: > > fput(file); > > This partially obsoletes the similar optimisation in inode_setattr(). I > guess the optimisation there retains some usefulness for O_TRUNC opens of > zero-length files, but for symettry and micro-efficiency, perhaps we should > remvoe the inode_setattr() test and check for i_size==0 in may_open()? Sounds like a good idea. That does simplify inode_setattr() nicely... Signed-off-by: Anton Altaparmakov --- linux-2.6/fs/attr.c.old 2005-10-31 09:29:38.000000000 +0000 +++ linux-2.6/fs/attr.c 2005-10-31 09:30:39.000000000 +0000 @@ -70,19 +70,10 @@ int inode_setattr(struct inode * inode, int error = 0; if (ia_valid & ATTR_SIZE) { - if (attr->ia_size != i_size_read(inode)) { - error = vmtruncate(inode, attr->ia_size); - if (error || (ia_valid == ATTR_SIZE)) - goto out; - } else { - /* - * We skipped the truncate but must still update - * timestamps - */ - ia_valid |= ATTR_MTIME|ATTR_CTIME; - } + error = vmtruncate(inode, attr->ia_size); + if (error || (ia_valid == ATTR_SIZE)) + goto out; } - if (ia_valid & ATTR_UID) inode->i_uid = attr->ia_uid; if (ia_valid & ATTR_GID) btw. Is it actually correct that we "goto out;" when "ia_valid == ATTR_SIZE"? That way we skip the mark_inode_dirty() call just before the "out" label... For ntfs at least that is fine because ntfs does an "inode_update_time(inode, 1)" unconditionally in ntfs_truncate() even when the size has not changed which calls mark_inode_dirty_sync() and when the size changes it also does a "__mark_inode_dirty(inode, I_DIRTY_SYNC | I_DIRTY_DATASYNC);" but I am not sure all filesystems are fine in that respect? Best regards, Anton -- Anton Altaparmakov (replace at with @) Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK Linux NTFS maintainer / IRC: #ntfs on irc.freenode.net WWW: http://linux-ntfs.sf.net/ & http://www-stu.christs.cam.ac.uk/~aia21/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/