From: Arjan van de Ven <arjan@infradead.org>
Subject: Re: [PATCH 3/3] Add timeout feature
Date: Wed, 9 Jul 2008 06:55:40 -0700
Message-ID: <20080709065540.57305d91@infradead.org>
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Cc: Theodore Tso <tytso@mit.edu>, Miklos Szeredi <miklos@szeredi.hu>,
	hch@infradead.org, pavel@suse.cz, t-sato@yk.jp.nec.com,
	akpm@linux-foundation.org, viro@ZenIV.linux.org.uk,
	linux-ext4@vger.kernel.org, xfs@oss.sgi.com, dm-devel@redhat.com,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	axboe@kernel.dk, mtk.manpages@googlemail.com
To: Dave Chinner <david@fromorbit.com>
In-Reply-To: <20080709114958.GV11558@disturbed>
Sender: linux-ext4-owner@vger.kernel.org

On Wed, 9 Jul 2008 21:49:58 +1000
Dave Chinner <david@fromorbit.com> wrote:

> 
> (e) none of the above.  The kernel compilation will appear to pause
> until the filesystem is unfrozen. No other visible effect should
> occur. It will get blocked in a write or filesystem transaction
> because the fs is frozen.
> 
> Look at vfs_check_frozen() - any call to that will block if the
> filesystem is frozen or being frozen. The generic hook is in
> __generic_file_aio_write_nolock() and various other filesystems have
> calls in their specific write paths (fuse, ntfs, ocfs2, xfs, xip) to
> do this.

yeah and mmap doesn't happen
> 
> For all other modifications, filesystem specific methods of
> blocking transactions are used. XFS uses vfs_check_frozen() in
> xfs_trans_alloc(), ext3 (and probably ocfs2) do it via
> their ->write_super_lockfs method calling journal_lock_updates(),
> ext4 via jbd2_lock_updates() and so on....

and what if it's the process that you need to unfreeze the fs later?
Good luck.

-- 
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