linux-ext4 - Re: ext2fs_block_iterate (e2, EXT2_RESIZE_INO, ...) => EXT2_ET_FILE_TOO

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Date:	Wed, 31 Aug 2011 22:59:22 +0700
From:	Ivan Shmakov <ivan@...y.siamics.net>
To:	linux-ext4@...r.kernel.org
Subject: Re: ext2fs_block_iterate (e2, EXT2_RESIZE_INO, ...) => EXT2_ET_FILE_TOO_BIG?

>>>>> Ted Ts'o <tytso@....edu> writes:

[…]

 > Yeah, the resize inode is a special case.  It is specially
 > constructed to reserve space for new block group descriptor blocks
 > when doing an online resize.  I would suggest for your purposes that
 > you _not_ support the online-resizable file system feature, as it's
 > unneeded complexity (from what I understand of what you're going to
 > be doing with the file system).

	I don't seem to understand why such a support would require a
	specific handling of the resizable filesystems (other than that
	EXT2_RESIZE_INO is to be ignored by e2dis.)

	As I currently have no means of Ext2+ FS non-payload parts
	extraction, I'm going to rely on e2image(8).  Like:

# tar -C / -jcf image.files.tar.bz2 mnt/ 

$ /sbin/e2image -r image.ext2 image.e2image 
$ e2dis image.index < image.ext2 

	Then, the image could be restored with:

$ tar -jxf image.files.tar.bz2 
$ find mnt/ -type f -print0 \
      | (cat < image.e2image && imrt image.index) \
      > image.ext2 

	(Note that imrt is going to lseek(2) its stdout.)

	That way, I assume that the resize inode is going to be
	preserved thanks to e2image.

	The point of the procedure above is that instead of passing a
	complete .tar.bz2 archive with all the files, only the new files
	may be passed, should it be necessary to produce a new version
	of the image (like passing a diff instead of the whole source.)
	Moreover, for system images, most of the files would likely to
	be available from the regular OS packages' repositories.

 > P.S. The code to create the reserved inode can be found in
 > lib/ext2fs/res_gdt.c, in ext2fs_create_resize_inode().

	ACK.  Thanks.

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