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List:       fuse-devel
Subject:    Re: [fuse-devel] Locking a filesystem for reorganization
From:       Mathias_Panzenböck
Date:       2011-09-28 22:02:59
Message-ID: 4E839993.60501 () gmx ! net
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Instead of completely locking, could you make it read only?

On 09/28/2011 11:00 PM, Stefan Westerfeld wrote:
>     Hi!
>
> I'm writing a filesystem with fuse that should store content hashes combined
> with history as representation of the files. So normally you can write new
> files and the contents are just stored. But once you run an external program,
> like
>
> $ bfsync2 commit
>
> I need to transform the file contents into hashes and update the history. I
> don't want the fuse filesystem to interfere with the reorganization.
>
> My first approach was to let the external program (bfsync2) write a special
> file called .bfsync/lock to the FUSE filesystem and write its own pid into the
> lock file. Then I added code into every bfsync_open/bfsync_read/...  function
> to simply wait for the pid to terminate and block.
>
> However, I've seen that this often causes problems: for instance under KDE4 (if
> I understood this correctly), the terminal emulator konsole tries to magically
> tell the user the working directory of the running process. Since the FUSE
> filesystem is locked during bfsync2 commit, konsole blocks (since all bfsync
> filesystem operations block). Since konsole blocks, the terminal output of
> bfsync2 commit isn't read anymore, so the commit also blocks. Deadlock. Only
> killing the bfsync2 commit process helps.
>
> Any suggestions of how to do this properly?
>
>     Cu... Stefan


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