From: Andrew Morton Subject: Re: [PATCH 0/3] freeze feature ver 1.6 Date: Tue, 24 Jun 2008 14:38:40 -0700 Message-ID: <20080624143840.c183d0d9.akpm@linux-foundation.org> References: <20080624155919t-sato@mail.jp.nec.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: axboe@kernel.dk, mtk.manpages@googlemail.com, linux-kernel@vger.kernel.org, xfs@oss.sgi.com, dm-devel@redhat.com, viro@ZenIV.linux.org.uk, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org To: Takashi Sato Return-path: In-Reply-To: <20080624155919t-sato@mail.jp.nec.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com List-Id: linux-ext4.vger.kernel.org On Tue, 24 Jun 2008 15:59:19 +0900 Takashi Sato wrote: > Hi Andrew and Alexander, > > I have implemented the ioctls for the filesystem freeze feature > and discussed its implementation on the ML (linux-ext4, xfs, > linux-fsdevel, linux-kernel) for five months. All of the comments are > addressed in my patch-set. > Could you consider merging it into Linux? > > The filesystem freeze feature can suspend accesses to the filesystem > keeping the filesystem's consistency. We can take the consistent backup > with it cooperating with the backup software. > > The patches are re-based from linux-2.6.26-rc3 to linux-2.6.26-rc7 > There is no functional change from the previous version. > The patch-set consists of the following three patches. > > [PATCH 1/3] Implement generic freeze feature > I have modified to set the suitable error number (EOPNOTSUPP) > in case the filesystem doesn't support the freeze feature. > > The ioctls for the generic freeze feature are below. > o Freeze the filesystem > int ioctl(int fd, int FIFREEZE, arg) > fd: The file descriptor of the mountpoint > FIFREEZE: request code for the freeze > arg: Ignored > Return value: 0 if the operation succeeds. Otherwise, -1 > > o Unfreeze the filesystem > int ioctl(int fd, int FITHAW, arg) > fd: The file descriptor of the mountpoint > FITHAW: request code for unfreeze > arg: Ignored > Return value: 0 if the operation succeeds. Otherwise, -1 > > [PATCH 2/3] Remove XFS specific ioctl interfaces for freeze feature > It removes XFS specific ioctl interfaces and request codes > for freeze feature. > This patch has been supplied by David Chinner. > > [PATCH 3/3] Add timeout feature > The timeout feature is added to freeze ioctl. And new ioctl > to reset the timeout period is added. > o Freeze the filesystem > int ioctl(int fd, int FIFREEZE, long *timeval) > fd: The file descriptor of the mountpoint > FIFREEZE: request code for the freeze > timeval: the timeout period in seconds > If it's 0 or 1, the timeout isn't set. > This special case of "1" is implemented to keep > the compatibility with XFS applications. > Return value: 0 if the operation succeeds. Otherwise, -1 > > o Reset the timeout period > This is useful for the application to set the timeval more accurately. > For example, the freezer resets the timeval to 10 seconds every 5 > seconds. In this approach, even if the freezer causes a deadlock > by accessing the frozen filesystem, it will be solved by the timeout > in 10 seconds and the freezer can recognize that at the next reset > of timeval. > int ioctl(int fd, int FIFREEZE_RESET_TIMEOUT, long *timeval) > fd:file descriptor of mountpoint > FIFREEZE_RESET_TIMEOUT: request code for reset of timeout period > timeval: new timeout period in seconds > Return value: 0 if the operation succeeds. Otherwise, -1 > Error number: If the filesystem has already been unfrozen, > errno is set to EINVAL. > > Any comments are very welcome. umm, OK, but nowhere in this patch series can I find a justification or reason for making these changes to Linux. Why do we want to do this? What is the benefit? What is the motivation. What are the use-cases, etc? Thanks.