linux-ext4 - Re: Mentor for a GSoC application wanted (Online ext2/3 filesystem checker)

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Message-ID: <480A42F6.2030005@redhat.com>
Date:	Sat, 19 Apr 2008 14:07:34 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Theodore Tso <tytso@....edu>
CC:	Alexey Zaytsev <alexey.zaytsev@...il.com>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Rik van Riel <riel@...riel.com>
Subject: Re: Mentor for a GSoC application wanted (Online ext2/3 filesystem
 checker)

Theodore Tso wrote:
> On Sat, Apr 19, 2008 at 01:44:51PM +0400, Alexey Zaytsev wrote:
>> If it is a block containing a metadata object fsck has already read,
>> than we already know what kind of object it is (there must be a way
>> to quickly find all cached objects derived from a given block), and
>> can update the cached version. And if fsck has not yet read the
>> block, it can just be ignored, no matter what kind of data it
>> contains. If it contains metadata and fsck is intrested in it, it
>> will read it sooner or later anyway. If it contains file data, why
>> should fsck even care?

It seems to me that what the proposed project really does, in essence,
is a read-only check of a filesystem snapshot.  It's just that the
snapshot is proposed to be constructed in a complex and non-generic (and
maybe impossible) way.

If you really just want to verify a snapshot of the fs at a point in
time, surely there are simpler ways.  If the device is on lvm, there's
already a script floating around to do it in automated fasion.  (I'd
pondered the idea of introducing META_WRITE (to go with META_READ) and
maybe lvm could do a "metadata-only" snapshot to be lighter weight?)

-Eric
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