Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758847AbXFRJPT (ORCPT ); Mon, 18 Jun 2007 05:15:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753946AbXFRJPH (ORCPT ); Mon, 18 Jun 2007 05:15:07 -0400 Received: from mx1.informatik.uni-tuebingen.de ([134.2.12.5]:35713 "EHLO mx1.informatik.uni-tuebingen.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752679AbXFRJPF (ORCPT ); Mon, 18 Jun 2007 05:15:05 -0400 X-Greylist: delayed 1159 seconds by postgrey-1.27 at vger.kernel.org; Mon, 18 Jun 2007 05:15:05 EDT From: Goswin von Brederlow To: "David Brown" Cc: fuse-devel@lists.sourceforge.net, "Linux Kernel Mailing List" Subject: Re: [fuse-devel] FS block count, size and seek offset? References: <9c21eeae0706171428u5a9ff79rad2b2083d3436d7f@mail.gmail.com> Date: Mon, 18 Jun 2007 10:55:39 +0200 In-Reply-To: <9c21eeae0706171428u5a9ff79rad2b2083d3436d7f@mail.gmail.com> (David Brown's message of "Sun, 17 Jun 2007 14:28:28 -0700") Message-ID: <87645lr69g.fsf@informatik.uni-tuebingen.de> User-Agent: Gnus/5.110006 (No Gnus v0.6) XEmacs/21.4.19 (linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2370 Lines: 71 "David Brown" writes: > I was looking at various file systems and how they return > stat.st_blocks and stat.st_size for directories and had some questions > on how a fuse filesystem is supposed to implement readdir with the > seek offset when trying to union two directories together. > > Is the offset a byte offset into the DIR *dp? or is it the struct > dirent size (which is relative based on the name of the file) into the > dir pointer? I think it is totaly your call what you store in it. Only requirement is that you never pass 0 to the filler function. off_t is 64bit so storing DIR* in it should be no problem. Or a pointer to struct UnionDIR { DIR *dp; struct UnionDIR *next; } > Also, if you want to be accurate when you stat a directory that's > unioned in the fuse file system how many blocks should one return? > Since each filesystem seems to return different values for size and > number of blocks for directories. I know I could just say that its not > supported with my filesystem built using fuse... but I'd like to at > least try to be accurate. You could add them up and round it to some common block size (if they differ). But I don't think it maters and nothing uses that info. What is more important is the link count. For example find uses the link count to know how many subdirs a directory has. Once it found that many it assumes there are no more dirs and saves on stat() calls. > Is it accurate to assume that the size or number of blocks returned > from a stat will be used to pass a seek offset? > > When does fuse use the seek offset? Afaik never. The offset is only stored for the next readdir call but never used inside fuse. > These are the number of blocks and size on an empty dir. > ext3 > size 4096 nblocks 8 > reiserfs > size 48 nblocks 0 > jfs > size 1 nblocks 0 > xfs > size 6 nblocks 0 > > Any help to figure out how to union two directories and return correct > values would be helpful. Why don't you use the existing fuse-unionfs? > Thanks, > - David Brown > > P.S. maybe a posix filesystem interface manual would be good? MfG Goswin - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/