From: Joel Becker Subject: Re: [Ocfs2-devel] [PATCH 1/3] ext3/ext4: Factor out disk addressability check Date: Thu, 12 Aug 2010 13:15:34 -0700 Message-ID: <20100812201534.GA22777@mail.oracle.com> References: <874ofr2myq.fsf@patl.com> <20100812174215.GC6561@mail.oracle.com> <1F3EDC08-AC93-4D4D-8F83-A13C418DFC88@dilger.ca> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Ted Ts'o" , Jan Kara , ocfs2-devel@oss.oracle.com, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, "linux-kernel@vger.kernel.org Patrick J. LoPresti" To: Andreas Dilger Return-path: Content-Disposition: inline In-Reply-To: <1F3EDC08-AC93-4D4D-8F83-A13C418DFC88@dilger.ca> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Thu, Aug 12, 2010 at 12:45:41PM -0600, Andreas Dilger wrote: > On 2010-08-12, at 11:42, 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; > >> + > >> + BUG_ON(blocksize_bits < 9); > >> + BUG_ON(blocksize_bits > PAGE_CACHE_SHIFT); > > I'd rather not have a BUG_ON() for a "check" function that may be called with on-disk values by some filesystem. Some filesystems (AFAIR) also handle blocksize > PAGE_SIZE internally, so this helper would not be useful for them. Filesystems that handle their own page cache certainly wouldn't be interested in a generic helper anyway. All of our pagecache assumes blocks between 512<->PAGE_CACHE_SIZE. If I change the BUG_ON()s to -EINVAL, does that work? Or do you have some way you'd like to allow non-pagecache filesystems to use this as well? Joel -- "I am working for the time when unqualified blacks, browns, and women join the unqualified men in running our government." - Sissy Farenthold Joel Becker Consulting Software Developer Oracle E-mail: joel.becker@oracle.com Phone: (650) 506-8127