linux-ext4 - Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super

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Date:	Fri, 19 Nov 2010 10:50:03 -0500
From:	Christoph Hellwig <hch@...radead.org>
To:	Ted Ts'o <tytso@....edu>, Christoph Hellwig <hch@...radead.org>,
	Mark Lord <kernel@...savvy.com>,
	Steven Whitehouse <swhiteho@...hat.com>,
	Lukas Czerner <lczerner@...hat.com>,
	James Bottomley <James.Bottomley@...e.de>,
	Matthew Wilcox <matthew@....cx>,
	Josef Bacik <josef@...hat.com>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	sandeen@...hat.com
Subject: Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate
 super_operation

On Fri, Nov 19, 2010 at 10:37:48AM -0500, Ted Ts'o wrote:
> I think the author of that slide deck was being a little hysterical.
> In nearly all of these cases, if the file system is comptently
> implemented (i.e., you don't do a trim on anything but a deleted file
> block, and _only_ when you know the deleted is committed, and only the
> filesystem --- not non-privileged users --- are allowed to use the
> TRIM command), there's no issue.

It's a huge issue for virtualization, where naive TRIM implementations
can expose data deleted in one VM to others.  It's also a huge issues
for RAIDs as mentioned by you.

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