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Re: [Cluster-devel] [PATCH] fs: push sync_filesystem() down to the file

To: Steven Whitehouse <swhiteho@xxxxxxxxxx>
Subject: Re: [Cluster-devel] [PATCH] fs: push sync_filesystem() down to the file system's remount_fs()
From: Theodore Ts'o <tytso@xxxxxxx>
Date: Thu, 13 Mar 2014 19:15:06 -0400
Cc: Jan Kara <jack@xxxxxxx>, jfs-discussion@xxxxxxxxxxxxxxxxxxxxx, Anders Larsen <al@xxxxxxxxxxx>, cluster-devel@xxxxxxxxxx, linux-mtd@xxxxxxxxxxxxxxxxxxx, Mikulas Patocka <mikulas@xxxxxxxxxxxxxxxxxxxxxxxx>, Petr Vandrovec <petr@xxxxxxxxxxxxxx>, codalist@xxxxxxxxxxxxxxxxxxxxxxxx, linux-cifs@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxx, Ext4 Developers List <linux-ext4@xxxxxxxxxxxxxxx>, Evgeniy Dushistov <dushistov@xxxxxxx>, Kees Cook <keescook@xxxxxxxxxxxx>, fuse-devel@xxxxxxxxxxxxxxxxxxxxx, reiserfs-devel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-nilfs@xxxxxxxxxxxxxxx, OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>, linux-nfs@xxxxxxxxxxxxxxx, Artem Bityutskiy <dedekind1@xxxxxxxxx>, linux-ntfs-dev@xxxxxxxxxxxxxxxxxxxxx, samba-technical@xxxxxxxxxxxxxxx, Adrian Hunter <adrian.hunter@xxxxxxxxx>, linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx, ocfs2-devel@xxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, Phillip Lougher <phillip@xxxxxxxxxxxxxxx>, linux-btrfs@xxxxxxxxxxxxxxx
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On Thu, Mar 13, 2014 at 04:28:23PM +0000, Steven Whitehouse wrote:
> 
> I guess the same is true for other file systems which are mounted ro
> too. So maybe a check for MS_RDONLY before doing the sync in those
> cases?

My original patch moved the sync_filesystem into the check for
MS_RDONLY in the core VFS code.  The objection was raised that there
might be some file system out there that might depend on this
behaviour.  I can't imagine why, but I suppose it's at least
theoretically possible.

So the idea is that this particular patch is *guaranteed* not to make
any difference.  That way there can be no question about the patch'es
correctness.

I'm going to follow up with a patch for ext4 that does exactly that,
but the idea is to allow each file system maintainer to do that for
their own file system.

I could do that as well for file systems that are "obviously"
read-only, but then I'll find out that there's some wierd case where
the file system can be used in a read-write fashion.  (Example: UDF is
normally used for DVD's, but at least in theory it can be used
read/write --- I'm told that Windows supports read-write UDF file
systems on USB sticks, and at least in theory it could be used as a
inter-OS exchange format in situations where VFAT and exFAT might not
be appropriate for various reasons.)

Cheers,

                                                - Ted

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