From: Theodore Tso Subject: Re: [PATCH 15/15][e2fsprogs] 64-bit mke2fs cleanup Date: Wed, 16 Jul 2008 12:31:48 -0400 Message-ID: <20080716163148.GC2167@mit.edu> References: <20080715164332.28567.27913.stgit@ichigo> <20080715165129.28567.7837.stgit@ichigo> <87tzeq0z95.fsf@frosties.localdomain> <20080716090931.6c8ca875@ichigo> <20080716145429.GA2167@mit.edu> <20080716101817.4d40a2f9@ichigo> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Goswin von Brederlow , linux-ext4@vger.kernel.org To: "Jose R. Santos" Return-path: Received: from www.church-of-our-saviour.org ([69.25.196.31]:42777 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756966AbYGPQbv (ORCPT ); Wed, 16 Jul 2008 12:31:51 -0400 Content-Disposition: inline In-Reply-To: <20080716101817.4d40a2f9@ichigo> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed, Jul 16, 2008 at 10:18:17AM -0500, Jose R. Santos wrote: > > It's really important when doing library design to think about future > > expandability. > > This would not be a API or ABI change so I don't see why another > renaming function would be needed. It also doesn't change the > behavior of ext2fs_get_device_size2() since it returns EFBIG when a > device is larger than what e2fsprogs currently supports, whether that > 48bit or 64bits. Putting the limit ext2fs_get_device_size2() avoid > folks from abusing something that probably isn't supported. E2fsprogs utilities are somewhat entitled to assume that they will be running with a version of libext2fs which is the same as the one that they shipped with --- although sometimes that assumption can be false, particularly when people are building a newer version of e2fsprogs from source and forget to install the newer libraries or forget to set LD_LIBRARY_PATH if they are building with dynamic libraries. However there may be other users of that interface, and they won't know if version of that library they are calling is set to return EFBIG on a 48bit or 64bit number. Besides, there may be other application users of that function where it would be useful to get the size of a device which is larger than 48-bits, even if mke2fs and ext4 today doesn't support it. This is just good library design not to enforce limits like this in a fairly generic function. Finally, in many programming discplines you *do* rename the function whenever you make major semantic changes to the function, not just for API or ABI changes. Otherwise a newer program might depend on ext2fs_get_device_size() returning a 64-bit size, and then it might get very confused or fail in unexpected ways if it is linked with an older library that returns EFBIG if the number is bigger than 48 bits. It's just a matter of how defensive you want to be in your programming, and how general-purpose you want you library routines to be. Regards, - Ted