linux-kernel - Re: Wrong DIF guard tag on ext2 write

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Message-ID: <yq17hmfy481.fsf@sermon.lab.mkp.net>
Date:	Thu, 03 Jun 2010 21:30:06 -0400
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Chris Mason <chris.mason@...cle.com>,
	James Bottomley <James.Bottomley@...e.de>,
	Matthew Wilcox <matthew@....cx>,
	Christof Schmitt <christof.schmitt@...ibm.com>,
	Boaz Harrosh <bharrosh@...asas.com>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: Wrong DIF guard tag on ext2 write

>>>>> "Nick" == Nick Piggin <npiggin@...e.de> writes:

Nick,

>> Filesystems will inevitably have to be integrity-aware for that to
>> work.  And it will be their job to keep the data pages stable during
>> DMA.

Nick> Closing the while it is dirty, while it is being written back
Nick> window still leaves a pretty big window. Also, how do you handle
Nick> mmap writes?  Write protect and checksum the destination page
Nick> after every store? Or leave some window between when the pagecache
Nick> is dirtied and when it is written back? So I don't know whether
Nick> it's worth putting a lot of effort into this case.

I'm mostly interested in the cases where the filesystem acts as a
conduit for integrity metadata from user space. 

I agree the corruption windows inside the kernel are only of moderate
interest.  No filesystems have added support for explicitly protecting a
bio because the block layer's function to do so automatically is just a
few function calls away.

-- 
Martin K. Petersen	Oracle Linux Engineering
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