From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bedivere.hansenpartnership.com ([66.63.167.143]:43716 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752249AbcEKDrp (ORCPT ); Tue, 10 May 2016 23:47:45 -0400 Message-ID: <1462938460.14896.32.camel@HansenPartnership.com> Subject: Re: [RFC v2 PATCH 0/8] VFS:userns: support portable root filesystems From: James Bottomley To: Al Viro Cc: Djalal Harouni , Chris Mason , tytso@mit.edu, Serge Hallyn , Josh Triplett , "Eric W. Biederman" , Andy Lutomirski , Seth Forshee , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Dongsu Park , David Herrmann , Miklos Szeredi , Alban Crequy Date: Tue, 10 May 2016 20:47:40 -0700 In-Reply-To: <20160511005340.GN2694@ZenIV.linux.org.uk> References: <1462372014-3786-1-git-send-email-tixxdz@gmail.com> <1462395979.14310.133.camel@HansenPartnership.com> <20160505073636.GA3357@dztty> <1462449388.2419.27.camel@HansenPartnership.com> <20160505214957.GA3071@dztty> <1462486085.2289.23.camel@HansenPartnership.com> <1462923416.14896.10.camel@HansenPartnership.com> <20160511005340.GN2694@ZenIV.linux.org.uk> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, 2016-05-11 at 01:53 +0100, Al Viro wrote: > On Tue, May 10, 2016 at 04:36:56PM -0700, James Bottomley wrote: > > +static int shiftfs_rename2(struct inode *olddir, struct dentry > > *old, > > + struct inode *newdir, struct dentry > > *new, > > + unsigned int flags) > > +{ > > + struct dentry *rodd = olddir->i_private, *rndd = newdir > > ->i_private, > > + *realold = old->d_inode->i_private, > > + *realnew = new->d_inode->i_private; > > + struct inode *realolddir = rodd->d_inode, *realnewdir = > > rndd->d_inode; > > + const struct inode_operations *iop = realolddir->i_op; > > + int err; > > + const struct cred *oldcred, *newcred; > > + > > + oldcred = shiftfs_new_creds(&newcred, old->d_sb); > > + err = iop->rename2(realolddir, realold, realnewdir, > > realnew, flags); > > + shiftfs_old_creds(oldcred, &newcred); > > ... and you've just violated all locking rules for ->rename2(). Yes, sorry, somehow I missed that when I converted everything else to the vfs_ functions. > > +static struct dentry *shiftfs_lookup(struct inode *dir, struct > > dentry *dentry, > > + unsigned int flags) > > +{ > > + struct dentry *real = dir->i_private, *new; > > + struct inode *reali = real->d_inode, *newi; > > + const struct cred *oldcred, *newcred; > > + > > + /* note: violation of usual fs rules here: dentries are > > never > > + * added with d_add. This is because we want no dentry > > cache > > + * for shiftfs. All lookups proceed through the dentry > > cache > > + * of the underlying filesystem, meaning we always see any > > + * changes in the underlying */ > > Bloody wonderful. So > * we lose caching the negative lookups We do? They should be cached in the underlying layer's dcache. If that's not enough, I can hash them, but I was trying to avoid doubling the dcache size. > * we've got buggered hardlinks (different inodes for those) Yes, had a note to do the lookup, but forgot. > * it has never, ever been tried on -next (would do rather nasty > things on that d_instantiate()) So this is just a proof of concept; I figured it was best to do it against current rather than have people who wanted to try it pull in your tree. I can respin it after the merge window closes. > > > + > > + kfree(sfc); > > + > > + return err; > > +} > > > + file->f_op = &sfc->fop; > > Lovely - now try that with underlying fs something built modular. > > Or try to use it on top of something with non-trivial > dentry_operations > (hell, on top of itself, for starters). So if I add the missing fops_get/put, you're happy with the way this hijacks f_op and f_inode? James