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

To: Jan Kara <jack@xxxxxxx>
Subject: Re: [Cluster-devel] [PATCH] fs: push sync_filesystem() down to the file system's remount_fs()
From: Steven Whitehouse <swhiteho@xxxxxxxxxx>
Date: Thu, 13 Mar 2014 16:28:23 +0000
Cc: "Theodore Ts'o" <tytso@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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In-reply-to: <20140313162319.GA504@xxxxxxxxxxxxx>
Organization: Red Hat UK Ltd
References: <20140313073936.GA14663@xxxxxxxxxxxxx> <1394720456-16629-1-git-send-email-tytso@xxxxxxx> <20140313162319.GA504@xxxxxxxxxxxxx>
Hi,

On Thu, 2014-03-13 at 17:23 +0100, Jan Kara wrote:
> On Thu 13-03-14 10:20:56, Ted Tso wrote:
> > Previously, the no-op "mount -o mount /dev/xxx" operation when the
>                                   ^^remount
> 
> > file system is already mounted read-write causes an implied,
> > unconditional syncfs().  This seems pretty stupid, and it's certainly
> > documented or guaraunteed to do this, nor is it particularly useful,
> > except in the case where the file system was mounted rw and is getting
> > remounted read-only.
> > 
> > However, it's possible that there might be some file systems that are
> > actually depending on this behavior.  In most file systems, it's
> > probably fine to only call sync_filesystem() when transitioning from
> > read-write to read-only, and there are some file systems where this is
> > not needed at all (for example, for a pseudo-filesystem or something
> > like romfs).
>   Hum, I'd avoid this excercise at least for filesystem where
> sync_filesystem() is obviously useless - proc, debugfs, pstore, devpts,
> also always read-only filesystems such as isofs, qnx4, qnx6, befs, cramfs,
> efs, freevxfs, romfs, squashfs. I think you can find a couple more which
> clearly don't care about sync_filesystem() if you look a bit closer.
> 
>
>                                                               Honza

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?

Steve.


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