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Re: question on new feature complexity/possibility/sensibility? (^ Alter

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: question on new feature complexity/possibility/sensibility? (^ Alternate)
From: Linda Walsh <xfs@xxxxxxxxx>
Date: Sun, 26 Jun 2011 21:08:41 -0700
Cc: xfs-oss <xfs@xxxxxxxxxxx>
In-reply-to: <20110627003209.GD32466@dastard>
References: <4E067D81.4070605@xxxxxxxxx> <20110627003209.GD32466@dastard>
User-agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv: Thunderbird/ Mnenhy/

Dave Chinner wrote:
So use a filesystem that supports them natively ;)
        Got any in in mind that also support acls, extended attrs
and has the reliability and performance of xfs?  ;-)

I.e. being able to hardlink files, but have an option to mark it as
copy on write -- allowing space to be save when copying directory trees,
but then dynamically making new copies when someone updates one of the
linked copies.

The problem is that a reflink sort of looks like a hard link, but in
many cases behaves like a soft link (e.g. different owners,
permissions, etc are possible) and hence - combined with the
copy-on-write behaviour - they need to be treated more like a
soft-link in terms of implementation.
        I can see this -- now this doesn't mean we are talking the same
type of reflink with the shared data above is it?  Cuz in this lower
case, I was talking about hmmm....interesting....

        I was thinking of just a copy-of-the whole file on write,
but that'd be a potential pain on some systems depending on the file
Soft links have their own
inode so can hold state separate to the inode they are pointing to,
and for reflinked files it is simply not practical to retroactively
modify the directory structure to point at a different inode when
the first COW operation occurs.
I see....

Like I said, it can be done, but it's not a small project. If you
want to sink a significant amount of development time to the
project, we will help you in any way we can. However, I don't think
anyone has the time to do something like this for you....
        If I had the time and mental resources...I'd love to.
But am a bit overwhelmed for time now, and even if I wasn't, I'd
not be anywhere near certain I'd be able to maintain continuous focus
for the length of time necessary to do that length of project.... if you know what I mean...

        Maybe certain if it was something that I or others could break
down into useful 'subchunks' that could go in at separate times.  Nothing
useless by itself (if nothing less than specific 'upgrading' of data infrastructure (data fields on disk, routines to parse such...etc),
but the whole thing at once seems pretty large.

(I know...I'm being a wimp)...

to support such things in the future

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