From: Joel Becker Subject: Re: [Ocfs2-devel] [PATCH 1/3] ext3/ext4: Factor out disk addressability check Date: Fri, 13 Aug 2010 13:47:01 -0700 Message-ID: <20100813204701.GB19568@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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andreas Dilger , "Ted Ts'o" , ocfs2-devel@oss.oracle.com, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, "linux-kernel@vger.kernel.org Patrick J. LoPresti" To: Jan Kara Return-path: Content-Disposition: inline In-Reply-To: <20100813163006.GB4329@quack.suse.cz> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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. Joel -- "I always thought the hardest questions were those I could not answer. Now I know they are the ones I can never ask." - Charlie Watkins Joel Becker Consulting Software Developer Oracle E-mail: joel.becker@oracle.com Phone: (650) 506-8127