From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda3.sgi.com [192.48.176.15]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id n11GQD5x194533 for ; Sun, 1 Feb 2009 10:26:14 -0600 Message-ID: <4985CCFA.4070008@panasas.com> Date: Sun, 01 Feb 2009 18:25:30 +0200 From: Boaz Harrosh MIME-Version: 1.0 Subject: Re: [xfs-masters] [PATCH] fs: Add new pre-allocation ioctls to vfs for compatibility with legacy xfs ioctls References: <4980C71F.1010804@ankitjain.org> <200901310138.34164.arnd@arndb.de> <20090130171423.f99c88d0.akpm@linux-foundation.org> <200901310248.42820.arnd@arndb.de> <49856FE6.8020601@panasas.com> <49857BEB.30404@panasas.com> <4985966D.8040402@panasas.com> <4985C1B0.8060905@sandeen.net> In-Reply-To: <4985C1B0.8060905@sandeen.net> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Eric Sandeen Cc: Arnd Bergmann , mfasheh@suse.com, joel.becker@oracle.com, linux-kernel@vger.kernel.org, hch@infradead.org, xfs-masters@oss.sgi.com, Geert Uytterhoeven , viro@zeniv.linux.org.uk, Ankit Jain , linux-fsdevel@vger.kernel.org, Andrew Morton , xfs@oss.sgi.com, ocfs2-devel@oss.oracle.com Eric Sandeen wrote: > Boaz Harrosh wrote: > > ... > >> I don't understand >> >> if you have a structure like >> struct foo { >> u32 one; >> u32 two; >> }; >> vs >> struct foo_packed { >> u32 one; >> u32 two; >> } __packed; >> >> Just adding an __attribute__((packed)) to it clearly does not change >> the layout of the structure. Are you saying the __attribute__((packed)) >> is an hint to the compiler that foo_packed might be used unaligned. This >> is just brain-dead, because I can use an unaligned pointer to foo just as >> I can to foo_packed. Otherwise there is no difference what-so-ever between >> the two. I have to see it to believe. It is totally the wrong hint in the >> wrong place taking away valuable meaning of saying "please don't use padding >> holes in this structure" >> >> Sorry for been so slow, I just don't get it. >> Boaz > > While I'm no gcc guru, I can confirm that gratuitous use of the packed > attribute is suboptimal; adding "packed" to every ondisk structure made > obdump -d xfs.ko | wc -l explode by about 15,000 lines on ia64. Yes! but are the structures the same? that is sizeof(foo_packed) == sizeof(foo) ? If not then clearly above is expected. In anyway, if __attribute__((packed)) makes some brain-dead gcc do the wrong thing putting a _Padding member where you expect an alignment hole, and a BUILD_BUG_ON(sizeof() != ()) statement somewhere in code is a must, specifically for the brain-dead. > > -Eric There are to many places in Kernel where these things are left to chance that give me an headache, not talking about cross platform mounts. Boaz _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs