From: Christoph Hellwig Subject: Re: [PATCH 1/6] statx: Add a system call to make enhanced file info available Date: Thu, 12 May 2016 02:12:49 -0700 Message-ID: <20160512091249.GB22420@infradead.org> References: <20160510070803.GC30896@infradead.org> <20160508083543.GA14316@infradead.org> <20160429125736.23636.47874.stgit@warthog.procyon.org.uk> <20160429125743.23636.85219.stgit@warthog.procyon.org.uk> <1734.1462801101@warthog.procyon.org.uk> <7963.1462869823@warthog.procyon.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Christoph Hellwig , linux-fsdevel@vger.kernel.org, linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org, samba-technical@lists.samba.org, linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org To: David Howells Return-path: Content-Disposition: inline In-Reply-To: <7963.1462869823@warthog.procyon.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Tue, May 10, 2016 at 09:43:43AM +0100, David Howells wrote: > Christoph Hellwig wrote: > > > All of these are easily available. But why special case them so that > > userspace must not ask for them? This makes an otherwise totally > > regular interface special now. Note that filesystems could always fill > > it out anyway and set it in the return mask. > > Because it would be a waste of bits in the mask. Is there a point in having > bits that are always going to be set unconditionally when we can just > *document* that these few fields are always going to be set. And what exaxtly is the cost of these bits? > So yes, you can look on it as there are special cases. However, if I can drop > stat emulation support, everything resolves down to the following classes: > > (1) Stuff that's unconditional: st_dev, st_blksize, st_information (maybe). > > (2) st_mode & S_IFMT. Unconditional or conditional? I'm not sure. > > (3) Stuff that's conditional: st_mode & ~S_IFMT, st_rdev, st_ino, ... > Basically everything else. If we at least go down to one set of conditional and one optional that's at least much better than what we currently have.