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

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Message-ID: <20110818210313.GA4602@thunk.org>
Date:	Thu, 18 Aug 2011 17:03:13 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Ivan Shmakov <oneingray@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: a (documented) way to get the Ext2+ filesystem size?

On Thu, Aug 18, 2011 at 10:49:38AM +0700, Ivan Shmakov wrote:
>  > 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.

Sorry, the documentation is not necessarily complete; my apologies.

> 	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.

The function to do this is in the 1.42 dev branch which is in Debian
unstable, and it's called ext2fs_block_count().

> 	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?

I make a very strong effort to ensure that interfaces which are
exposed via the shared library are stable.  If you're not sure, please
feel free to ask on the ext4 list.

Regards,

					- Ted
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