linux-kernel - Re: [PATCH 05/22][RFC] Unionfs: Copyup Functionality

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Message-ID: <Pine.LNX.4.61.0609170023500.24270@yvahk01.tjqt.qr>
Date:	Sun, 17 Sep 2006 00:26:22 +0200 (MEST)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	Josef Sipek <jsipek@....cs.sunysb.edu>
cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	hch@...radead.org, akpm@...l.org, viro@....linux.org.uk
Subject: Re: [PATCH 05/22][RFC] Unionfs: Copyup Functionality

>> >> Is BUG the right thing, what do others think? (Using WARN, and set err to
>> >> something useful?)
>> > 
>> >Well, it is definitely a condition which Unionfs doesn't expect - if it
>> >doesn't know about the type, how could it copy it up?
>> 
>> Other filesystems don't seem to BUG either (at least I have not run into 
>> that yet) when - for whatever reasons - the statdata of a dentry is 
>> fubared. `ls`  just displays it then, like
>> 
>>  ?-w---Sr-T 1 root root 4294967295 date fubared_file
>
>I was thinking about this, and the difference between "other filesystems"
>and unionfs in this case is that the example above is just stat. During
>copyup, unionfs has to copy the file to another filesystem. How is it
>supposed to do that when it doesn't understand what the file is?
>
>Sure, when unionfs does stat, fubared statdata is fine, but during
>copyup...bad things could potentially happen.
>
>Any suggestions how to copyup an unknown file type?

Return some error value if possible. -EIO, banners, big printk()s,
anything. Tell the user the filesytem on some branch is hosed - or
too advanced to be understood by unionfs. (There seems to be a
variety of file types in other UNIXes according to `man 2 stat`,
such as doors, etc.)



Jan Engelhardt
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