linux-ext4 - Re: [PATCH 07/36 v4] libext2fs: add inline

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Message-ID: <20120813080750.GB21093@gmail.com>
Date:	Mon, 13 Aug 2012 16:07:50 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Theodore Ts'o <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org, Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [PATCH 07/36 v4] libext2fs: add inline_data file

On Tue, Aug 07, 2012 at 02:40:02PM -0400, Theodore Ts'o wrote:
> One major comment about the library functions.  The reason why we have
> functions of the form ext2fs_foo(), ext2fs_foo2(), ext2fs_foo3(),
> etc. is to preserve backwards compatibility of the ABI.  In general,
> ext2fs_foo2() will have an extra parameter which wasn't in
> ext2fs_foo(), and ext2fs_foo2() will have a superset of the
> functionality of ext2fs_foo().  If later we need to add to add another
> parameter to further extend the functionality of the function, we
> might have an ext2fs_foo3(), which again will be a supserset of the
> functionality of ext2fs_foo2().   
> 
> So in general, we only need to implement ext2fs_fooN(), and then
> ext2fs_fooX where 0 <= X <= N simply call ext2fs_fooN with the extra
> parameters defaulted out (usually to 0 or NULL).
> 
> It also follows that when we create a new function, there's no need to
> do this.  So the fact that you have an ext2fs_inlinedata_iterate()
> which just calls ext2fs_inline_data_iterate2() is not something you
> need to do.
> 
> More seriously, ext2fs_inline_data_iterate3() has an implementation
> which is completely different from that of
> ext2fs_inline_data_iterate2(), and that's an immediate red flag.  This
> means that these two functions are semantically different, and so they
> should have fundamentally different names --- or you need to make
> ext2fs_inline_data_iterate3() a strict superset of the functionality
> of ext2fs_inline_data_iterate2().
> 
> Also, I note that there are a number of patches which basically do
> this:
> 
> -	retval = ext2fs_dir_iterate2(current_fs, inode_num, 0,
> -				    0, rmdir_proc, &rds);
> +	if (ext2fs_has_inline_data(current_fs, inode_num))
> +		retval = ext2fs_inline_data_iterate2(current_fs, inode_num, 0,
> +						     0, rmdir_proc, &rds);
> +	else
> +		retval = ext2fs_dir_iterate2(current_fs, inode_num, 0,
> +					    0, rmdir_proc, &rds);
> 
> The much better thing to do is to make ext2fs_dir_iterate2() check to
> see if the inode has inline data, and if so, to call
> ext2fs_inline_data_iterate2() directly.   This has a couple of benefits.
> 
> The first is it will reduce the number of patches we need to apply.
> More importantly, it means that existing programs that don't know
> about inline data, but who happen to use ext2fs_dir_iterate(), will be
> able to work automatically, without requiring code changes.  It's also
> much cleaner from a conceptual point of view, since the
> ext2fs_dir_iterate abstraction shouldn't need to expose to the user
> whether the directory data is inline or in a separate data block.

Thanks for patient explanation.  I will fix the patches according to
your advice.

Regards,
Zheng
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