From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Subject: [RFC][take 3] e2fsprogs: Add ext4migrate
Date: Tue, 10 Apr 2007 14:00:51 +0530
Message-ID: <1176193853165-git-send-email-aneesh.kumar@linux.vnet.ibm.com>
Cc: aneesh.kumar@linux.vnet.ibm.com
To: linux-ext4@vger.kernel.org
Sender: linux-ext4-owner@vger.kernel.org

This is work in progress


Changes from from my previous patches are as follows:
a) Mark the file system unclean if we fail migrating
b) support for migrating more than one file
c) Support for migrating all the ext3 inode in the file system
d) Fix the free block counts. ( Make sure fsck pass without errors after migration )
e) Mark the blocks used for extent idx as used so that we don't double allocate them
f) Don't mark the blocks used for indirect block map as free untill we fully migrate
   the inode.This make sure we don't use these blocks for extent idx and overwrite them.
g) Fix the migration when we end up with more than one extent idx block.


Changes from from my previous patches are as follows:
a) support for files with holes
b) use the block iterator present in libext2fs
c) don't mark  the indirect blocks as unused early. If we mark the
   the blocks unused, they can be resued for extent index. If we later
   fail to migrate, the indirect blocks content would be overwritten.

The below patches add ext4migrate utility that helps in migrating
a ext3 block mapped inode to ext4 extent mapped inode. I have split
the patches into two. The purpose of splitting the patches into two
is to make the review easeir. The contents of [PATCH 1/2] is derived out of kernel source.

ext4migrate command takes the below syntax
ext4migrate --display | --migrate  <image_name> [<filename>]

The --display option helps in displaying the block map details for an ext3 inode
and extent map details for an ext4 inode. The --migrate option convert a block mapped
ext3 inode to extent mapped ext4 inode.

This needs to be run on an unmounted file system (offline migration).

The extent insert code is derived out of the latest ext4 kernel source. I have tried
to keep the code as close as possible to the kernel sources. This makes sure that any
fixes for the tree building code in kernel should be easily applied to ext4migrate.
The ext3_ext naming convention instead of ext4_ext found in kernel is to
make  sure we are in sync with rest of e2fsprogs source.

The inode modification is done only at the last stage. This is to make sure that if we
fail at any intermediate stage, we exit without touching the disk.

The inode update is done as below
a) Walk the extent index blocks and write them to the disk. If failed exit
b) Writ the update block bitmap. if failed exit.
b) Write the inode. if failed Undo the write of block bitmap and exit.

I will be looking at the writing a new COW unix io manager that will take a backup
of blocks modified. This will help us to easily recover the file system in case
we fail and overwrite some of the blocks. (more info  e2fsprogs-upstream/TODO)

The patch applies on top of e2fsprogs found at

http://www.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs-interim/e2fsprogs-1.39-tyt1/e2fsprogs-1.39-tyt1.tar.bz2

-aneesh