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Re: [PATCH 3/3] Add timeout feature

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 3/3] Add timeout feature
From: Arjan van de Ven <arjan@xxxxxxxxxxxxx>
Date: Wed, 9 Jul 2008 06:55:40 -0700
Cc: Theodore Tso <tytso@xxxxxxx>, Miklos Szeredi <miklos@xxxxxxxxxx>, hch@xxxxxxxxxxxxx, pavel@xxxxxxx, t-sato@xxxxxxxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx, viro@xxxxxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, dm-devel@xxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, axboe@xxxxxxxxx, mtk.manpages@xxxxxxxxxxxxxx
In-reply-to: <20080709114958.GV11558@disturbed>
Organization: Intel
References: <20080709005254.GQ11558@disturbed> <20080709010922.GE9957@xxxxxxx> <E1KGSvZ-0006dB-53@xxxxxxxxxxxxxxxxxxx> <20080709061621.GA5260@xxxxxxxxxxxxx> <E1KGT4q-0006fD-Jb@xxxxxxxxxxxxxxxxxxx> <20080708234120.5072111f@xxxxxxxxxxxxx> <E1KGTTm-0006ke-Jh@xxxxxxxxxxxxxxxxxxx> <20080708235502.1c52a586@xxxxxxxxxxxxx> <20080709071346.GS11558@disturbed> <20080709110900.GI9957@xxxxxxx> <20080709114958.GV11558@disturbed>
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On Wed, 9 Jul 2008 21:49:58 +1000
Dave Chinner <david@xxxxxxxxxxxxx> 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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