From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Subject: Re: [GIT PULL] Ceph fixes for 5.1-rc7 Date: Sun, 28 Apr 2019 15:48:50 +0100 Message-ID: <20190428144850.GA23075@ZenIV.linux.org.uk> References: <20190425174739.27604-1-idryomov@gmail.com> <342ef35feb1110197108068d10e518742823a210.camel@kernel.org> <20190425200941.GW2217@ZenIV.linux.org.uk> <86674e79e9f24e81feda75bc3c0dd4215604ffa5.camel@kernel.org> <20190426165055.GY2217@ZenIV.linux.org.uk> <20190428043801.GE2217@ZenIV.linux.org.uk> <7bac7ba5655a8e783a70f915853a0846e7ff143b.camel@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <7bac7ba5655a8e783a70f915853a0846e7ff143b.camel@kernel.org> Sender: linux-kernel-owner@vger.kernel.org To: Jeff Layton Cc: Linus Torvalds , Ilya Dryomov , ceph-devel@vger.kernel.org, Linux List Kernel Mailing , linux-cifs List-Id: ceph-devel.vger.kernel.org On Sun, Apr 28, 2019 at 09:27:20AM -0400, Jeff Layton wrote: > I don't see a problem doing what you suggest. An offset + fixed length > buffer would be fine there. > > Is there a real benefit to using __getname though? It sucks when we have > to reallocate but I doubt that it happens with any frequency. Most of > these paths will end up being much shorter than PATH_MAX and that slims > down the memory footprint a bit. AFAICS, they are all short-lived; don't forget that slabs have cache, so in that situation allocations are cheap. > Also, FWIW -- this code was originally copied from cifs' > build_path_from_dentry(). Should we aim to put something in common > infrastructure that both can call? > > There are some significant logic differences in the two functions though > so we might need some sort of callback function or something to know > when to stop walking. Not if you want it fast... Indirect calls are not cheap; the cost of those callbacks would be considerable. Besides, you want more than "where do I stop", right? It's also "what output do I use for this dentry", both for you and for cifs (there it's "which separator to use", in ceph it's "these we want represented as //")... Can it be called on detached subtree, during e.g. open_by_handle()? There it can get really fishy; you end up with base being at the random point on the way towards root. How does that work, and if it *does* work, why do we need the whole path in the first place? BTW, for cifs there's no need to play with ->d_lock as we go. For ceph, the only need comes from looking at d_inode(), and I wonder if it would be better to duplicate that information ("is that a snapdir/nosnap") into dentry iself - would certainly be cheaper. OTOH, we are getting short on spare bits in ->d_flags...