linux-ext4 - Re: a (documented) way to get the Ext2+ filesystem size?

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Message-ID: <86ei0jxtt9.fsf@gray.siamics.net>
Date:	Thu, 18 Aug 2011 10:49:38 +0700
From:	Ivan Shmakov <ivan@...y.siamics.net>
To:	linux-ext4@...r.kernel.org
Subject: Re: a (documented) way to get the Ext2+ filesystem size?

>>>>> Ted Ts'o <tytso@....edu> writes:
>>>>> On Thu, Aug 18, 2011 at 01:50:48AM +0700, Ivan Shmakov wrote:

[…]

 >> The intent is to process a filesystem image, not a mounted
 >> filesystem.  It's my understanding that I cannot use neither
 >> statfs(2) nor POSIX' statvfs(2) in this case.

 >> The code I've posted earlier is used in my e2dis [1–3] project.

 > For this, I'd suggest that you use the ext2fs library.  That will
 > take care of byte swapping, etc.  It also means that you don't have
 > to worry about parsing the extent trees.  If you had used the ext2fs
 > library before ext4 had shipped, you wouldn't have had to make any
 > changes to support extents, since the ext2fs library wraps and
 > provides abstract interfaces for most of what you would need for
 > e2dis project.

	I don't seem to understand.  I've scanned through the
	(libext2fs.info) Function Index section (as per the Debian's
	e2fslibs-dev package, 1.41.12-2), and I see no mention of a
	function that I can use for that.

	Thus, I've ended up writing my own one, which takes an
	ext2_filsys handle, and references, via its ‘super’ member, the
	‘s_blocks_count’ and ‘s_blocks_count_hi’ members of the
	superblock structure.

	However, I was concerned that I don't seem to find the
	documentation for these structures' contents anywhere.  (Sans
	the source, of course), and wondered, if the interface I use is
	at least stable?

	TIA.

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