From mboxrd@z Thu Jan 1 00:00:00 1970 From: Amir Goldstein Subject: Re: [PATCH v2 05/11] ovl: lookup redirect by file handle Date: Wed, 26 Apr 2017 13:17:58 +0300 Message-ID: References: <1493025256-27188-1-git-send-email-amir73il@gmail.com> <1493025256-27188-6-git-send-email-amir73il@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org To: Miklos Szeredi Cc: Vivek Goyal , Al Viro , "linux-unionfs@vger.kernel.org" , linux-fsdevel List-Id: linux-unionfs@vger.kernel.org On Wed, Apr 26, 2017 at 12:55 PM, Miklos Szeredi wrote: > On Wed, Apr 26, 2017 at 11:40 AM, Amir Goldstein wrote: > >> Just to see that I understand you correctly. >> >> I am now working on storing the following: >> >> /* >> * The tuple origin.{fh,layer,uuid} is a universal unique identifier >> * for a copy up origin, where: >> * origin.fh - exported file handle of the lower file >> * origin.root - exported file handle of the lower layer root >> * origin.uuid - uuid of the lower filesystem > > I wouldn't even store origin.root. > >> * >> * origin.{fh,root} are stored in format of a variable length binary blob >> * with struct ovl_fh header (total blob size up to 20 bytes). >> * uuid is stored in raw format (16 bytes) as published by sb->s_uuid. >> */ >> >> I intend to implement lookup as follows: >> - compare(origin.uuid, same_lower_sb->s_uuid) >> # layer root dentries cannot be DCACHE_DISCONNECTED, so >> # exportfs_decode_fh ignores mnt arg and returns the cached dentry >> - root = exportfs_decode_fh(lowerstack[0].mnt, origin.root) >> - find layer where lowerstack[layer].dentry == root >> - this = exportfs_decode_fh(lowerstack[layer].mnt, origin.fh) >> >> is_subdir() is NOT needed for decoding the layer root >> is_subdir() is optional for decoding the lower file, because >> it is not needed to identify the layer > > Hmm, we can just force exportfs_decode_fh() to return a connected > dentry (return false from *acceptable() if the dentry is disconnected) > before going on to iterate the layers to see which one contains it. > Hmm, this might work, but to quote from exportfs_decode_fh(): "It's not a directory. Life is a little more complicated." IIUC, 'connected' means 'connected to sb root', and not 'connected to mnt root', so in the optimal case where all lower dentries are cached, exportfs_decode_fh() will return a connected dentry for every fh we give it regardless of the mnt argument, so we will have to use is_subdir() to find the right layer, which brings us back to O(numlower*depth) With the extra cost of storing the deducible information origin.root, we will have less complex and more efficient lookup code. Let me try and implement it and see if I am right. We can always discard origin.root from v4 if it turns out to be unhelpful. Amir.