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Re: low level access path for xfs operation

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: low level access path for xfs operation
From: Soon-Son Kwon <kss@xxxxxxxx>
Date: Fri, 21 Mar 2003 19:43:53 +0900
Cc: Soon-Son Kwon <kss@xxxxxxxx>, linux-xfs@xxxxxxxxxxx
In-reply-to: <20030321091423.A28976@xxxxxxxxxxxxx>; from hch@xxxxxxxxxxxxx on Fri, Mar 21, 2003 at 09:14:23AM +0000
Organization: KLDP(Korean Linux Documentation Project)
References: <20030321124047.A26767@xxxxxxxxxxxxx> <20030321091423.A28976@xxxxxxxxxxxxx>
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On Fri, Mar 21, 2003 at 09:14:23AM +0000, Christoph Hellwig wrote:
> On Fri, Mar 21, 2003 at 12:40:47PM +0900, Soon-Son Kwon wrote:
> > Hi xfs folks:
> > Could anyone please let me know the following
> > xfs internal operation details?
> > 
> > I would like to know if there is any operation
> > that bypasses submit_bio() when accessing the 
> > lower level block devices.
> 
> No, there is no such operation.
> 
> > I want to add some function whenever the filesystem
> > tries to modify any block and concluded that submit_bio()
> > seems to be the lowest entry point for such operations.
> 
> You might want to rewrite a block remapper like dm or md
> instead of modifying core core..

What I would like to implement is the snapshot functionality
within the filesystem. I know LVM supports snapshot but
it requires a separate volume for each snapshot. I thought
snapshot within the filesystem would be more convenient.

Snapshot functionality requires copy-on-write implementation
when something tries to modify any block, copy the old content
to new block and overwrite the new content to that block
while the snapshot image keeps track of the original content.

Anyway, do you think implementing that operation requires
modifying dm/md code instead of modifying submit_bio()?

Any comment is welcomed 
and thank you very much for answering my question.....
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