From: Joel Becker Subject: Re: [Ocfs2-devel] [PATCH 1/3] ext3/ext4: Factor out disk addressability check Date: Fri, 13 Aug 2010 15:52:46 -0700 Message-ID: <20100813225246.GC19568@mail.oracle.com> References: <874ofr2myq.fsf@patl.com> <20100812174215.GC6561@mail.oracle.com> <1F3EDC08-AC93-4D4D-8F83-A13C418DFC88@dilger.ca> <20100812201534.GA22777@mail.oracle.com> <209AEA97-E284-4ADB-8774-50C2630606B9@dilger.ca> <20100812222949.GC22777@mail.oracle.com> <20100813163006.GB4329@quack.suse.cz> <20100813204701.GB19568@mail.oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: Jan Kara , Andreas Dilger , "Ted Ts'o" , ocfs2-devel@oss.oracle.com, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, "linux- Return-path: Received: from rcsinet10.oracle.com ([148.87.113.121]:17622 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755732Ab0HMWxn (ORCPT ); Fri, 13 Aug 2010 18:53:43 -0400 Content-Disposition: inline In-Reply-To: <20100813204701.GB19568@mail.oracle.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, Aug 13, 2010 at 01:47:01PM -0700, Joel Becker wrote: > On Fri, Aug 13, 2010 at 06:30:07PM +0200, Jan Kara wrote: > > On Thu 12-08-10 15:29:49, Joel Becker wrote: > > > +/** > > > + * generic_check_addressable - Check addressability of file system > > > + * @blocksize_bits: log of file system block size > > > + * @num_blocks: number of blocks in file system > > > + * > > > + * Determine whether a file system with @num_blocks blocks (and a > > > + * block size of 2**@blocksize_bits) is addressable by the sector_t > > > + * and page cache of the system. Return 0 if so and -EFBIG otherwise. > > > + */ > > > +int generic_check_addressable(unsigned blocksize_bits, u64 num_blocks) > > > +{ > > > + u64 last_fs_block = num_blocks - 1; > > > + > > > + if (unlikely(num_blocks == 0)) > > > + return 0; > > > + > > > + if ((blocksize_bits < 9) || (blocksize_bits > PAGE_CACHE_SHIFT)) > > > + return -EINVAL; > > > + > > > + if ((last_fs_block > > > > + (sector_t)(~0ULL) >> (blocksize_bits - 9)) || > > > + (last_fs_block > > > > + (pgoff_t)(~0ULL) >> (PAGE_CACHE_SHIFT - blocksize_bits))) { > > ^^^ I don't get the pgoff_t check. Shouldn't it rather be > > (u64)(pgoff_t)(~0ULL) << (PAGE_CACHE_SHIFT - blocksize_bits)? > > Because on 32-bit arch we are able to address 16TB device, which is for 1KB > > blocksize 1<<34 blocks. But your math gives 1<<30 blocks... > > This code is directly lifted from ext4. But that said, I am > starting to think you're right. 1 page == 4 x 1K blocks, rather than 4 > pages == 1 1K block. Wouldn't it rather be: ... || ((last_fs_block >> (PAGE_CACHE_SHIFT - blocksize_bits)) > (pgoff_t)(!0ULL))) { Joel -- "What no boss of a programmer can ever understand is that a programmer is working when he's staring out of the window" - With apologies to Burton Rascoe Joel Becker Consulting Software Developer Oracle E-mail: joel.becker@oracle.com Phone: (650) 506-8127