From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?utf-8?B?SsO2cm4=?= Engel <joern@logfs.org>
Subject: Re: Proposal to improve filesystem/block snapshot interaction
Date: Tue, 30 Oct 2007 15:06:25 +0100
Message-ID: <20071030140624.GA13455@lazybastard.org>
References: <20070927063113.GD2989@sgi.com> <20071030010453.GF27385@sgi.com> <7fe698080710300235v3ce49613nfe3c5e733f1b6f5b@mail.gmail.com>
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Cc: Greg Banks <gnb@sgi.com>,
	Linux Filesystem Mailing List <linux-fsdevel@vger.kernel.org>,
	David Chinner <dgc@melbourne.sgi.com>,
	Donald Douwsma <donaldd@melbourne.sgi.com>,
	Christoph Hellwig <hch@infradead.org>,
	Roger Strassburg <rls@sgi.com>, Mark Goodwin <markgw@sgi.com>,
	Brett Jon Grandbois <brettg@melbourne.sgi.com>,
	Arnd Bergmann <arnd@arndb.de>
To: Dongjun Shin <djshin90@gmail.com>
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On Tue, 30 October 2007 18:35:08 +0900, Dongjun Shin wrote:
> On 10/30/07, Greg Banks <gnb@sgi.com> wrote:
> >
> > BIO_HINT_RELEASE
> >     The bio's block extent is no longer in use by the filesystem
> >     and will not be read in the future.  Any storage used to back
> >     the extent may be released without any threat to filesystem
> >     or data integrity.
>=20
> I'd like to second the proposal, but it would be more useful to bring=
 the hint
> down to the physical devices.

Absolutely.  Logfs would love to have an erase operation for block
devices as well.  However the above doesn't quite match my needs,
because the blocks _will_ be read in the future.

There are two reasons for reading things back later.  The good one is t=
o
determine whether the segment was erased or not.  Reads should return
either valid data or one of (all-0xff, all-0x00, -ESOMETHING).  Having
a dedicated error code would be best.

And getting the device erasesize would be useful as well, for obvious
reasons.

J=C3=B6rn

--=20
When you close your hand, you own nothing. When you open it up, you
own the whole world.
-- Li Mu Bai in Tiger & Dragon
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