From: Eric Sandeen Subject: Re: [PATCH] vfs: allow custom EOF in generic_file_llseek code Date: Fri, 27 Apr 2012 11:28:58 -0500 Message-ID: <4F9AC94A.3070506@sandeen.net> References: <4F9AC770.8080004@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "linux-fsdevel@vger.kernel.org" , ext4 development , Andreas Dilger , Bernd Schubert To: Eric Sandeen Return-path: Received: from sandeen.net ([63.231.237.45]:49330 "EHLO mail.sandeen.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758889Ab2D0Q27 (ORCPT ); Fri, 27 Apr 2012 12:28:59 -0400 In-Reply-To: <4F9AC770.8080004@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 4/27/12 11:21 AM, Eric Sandeen wrote: > For ext3/4 htree directories, using the vfs llseek function with > SEEK_END goes to i_size like for any other file, but in reality > we want the maximum possible hash value. Recent changes > in ext4 have cut & pasted generic_file_llseek() back into fs/ext4/dir.c, > but replicating this core code seems like a bad idea, especially > since the copy has already diverged from the vfs. > > This patch implements a version of generic_file_llseek which can accept > both a custom maximum offset, and a custom EOF position. With this > in place, ext4_dir_llseek can pass in the appropriate maximum hash > position for both maxsize and eof, and get what it wants. > > As far as I know, this does not fix any bugs - nfs in the kernel > doesn't use SEEK_END, and I don't know of any user who does. But > some ext4 folks seem keen on doing the right thing here, and I can't > really argue. > > (Patch also fixes up some comments slightly) > > Signed-off-by: Eric Sandeen I guess I should ahev done a patch series, although the ext4 patch is so messy it's hard to read as a patch. With the new framework in place, ext4_dir_llseek can just be: /* * ext4_dir_llseek() calls generic_file_llseek_size to handle htree * directories, where the "offset" is in terms of the filename hash * value instead of the byte offset. * * Because we may return a 64-bit hash that is well beyond offset limits, * we need to pass the max hash as the maximum allowable offset in * the htree directory case. * * For non-htree, ext4_llseek already chooses the proper max offset. */ loff_t ext4_dir_llseek(struct file *file, loff_t offset, int origin) { struct inode *inode = file->f_mapping->host; int dx_dir = is_dx_dir(inode); loff_t htree_max = ext4_get_htree_eof(file); if (likely(dx_dir)) return generic_file_llseek_size_eof(file, offset, origin, htree_max, htree_max); else return ext4_llseek(file, offset, origin); } -Eric