On Mon, 21 Jun 2010, Ian Kent wrote: > On Wed, 2010-06-16 at 12:04 +0800, Ian Kent wrote: > > On Tue, 2010-06-15 at 11:39 -0700, Valerie Aurora wrote: > > > From: Jan Blunck <[email protected]> > > > > > > XXX - This is broken and included just to make union mounts work. See > > > discussion at: > > > > > > http://kerneltrap.org/mailarchive/linux-fsdevel/2010/1/15/6708053/thread > > > > Instead of saving the vfsmount we could save a pointer to the dentry of > > the mount point in the autofs super block info struct. I think that's > > the bit I don't have so it would be sufficient for a lookup_mnt() for > > the needed vfsmount in ->follow_mount(). > > > > Objections? > > Suggestions? > > No comments so far. > > Before I dive into testing if this actually does what I need, can I get > an "in principal" ack or nack for the patch so union mounts can move on > please? > > Note that this patch hasn't even been compile tested so the point is to > decide whether it is worth going ahead with it.
mnt_mountpoint is NULL at the point you try to save it, so this is not going to work. > > > autofs4 - save autofs trigger mountpoint in super block info > > From: Ian Kent <[email protected]> > > Adapted from the original patch from Jan Blunck <[email protected]>. > > Original commit message: > > This is a bugfix/replacement for commit > 051d381259eb57d6074d02a6ba6e90e744f1a29f: > > During a path walk if an autofs trigger is mounted on a dentry, > when the follow_link method is called, the nameidata struct > contains the vfsmount and mountpoint dentry of the parent mount > while the dentry that is passed in is the root of the autofs > trigger mount. I believe it is impossible to get the vfsmount of > the trigger mount, within the follow_link method, when only the > parent vfsmount and the root dentry of the trigger mount are > known. > > The solution in this commit was to replace the path embedded in the > parent's nameidata with the path of the link itself in > __do_follow_link(). This is a relatively harmless misuse of the > field, but union mounts ran into a bug during follow_link() caused by > the nameidata containing the wrong path (we count on it being what it > is all other places - the path of the parent). > > A cleaner and easier to understand solution is to save the necessary > mountpoint dentry in the autofs superblock info when it is mounted. > Then we can cwlookup the needed vfsmount in autofs4_follow_link(). > > Signed-off-by: Ian Kent <[email protected]> > Cc: Jan Blunck <[email protected]> > Cc: Valerie Aurora <[email protected]> > Cc: Alexander Viro <[email protected]> > Cc: [email protected] > --- > > fs/autofs4/autofs_i.h | 1 + > fs/autofs4/init.c | 11 ++++++++++- > fs/autofs4/root.c | 13 +++++++++++++ > fs/namei.c | 7 ++----- > fs/namespace.c | 1 + > 5 files changed, 27 insertions(+), 6 deletions(-) > > > diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h > index 3d283ab..9fc6d69 100644 > --- a/fs/autofs4/autofs_i.h > +++ b/fs/autofs4/autofs_i.h > @@ -133,6 +133,7 @@ struct autofs_sb_info { > int reghost_enabled; > int needs_reghost; > struct super_block *sb; > + struct dentry *mountpoint; > struct mutex wq_mutex; > spinlock_t fs_lock; > struct autofs_wait_queue *queues; /* Wait queue pointer */ > diff --git a/fs/autofs4/init.c b/fs/autofs4/init.c > index 9722e4b..f305b7d 100644 > --- a/fs/autofs4/init.c > +++ b/fs/autofs4/init.c > @@ -17,7 +17,16 @@ > static int autofs_get_sb(struct file_system_type *fs_type, > int flags, const char *dev_name, void *data, struct vfsmount *mnt) > { > - return get_sb_nodev(fs_type, flags, data, autofs4_fill_super, mnt); > + struct autofs_sb_info *sbi; > + int ret; > + > + ret = get_sb_nodev(fs_type, flags, data, autofs4_fill_super, mnt); > + if (ret) > + return ret; > + > + sbi = autofs4_sbi(mnt->mnt_sb); > + sbi->mountpoint = mnt->mnt_mountpoint; > + return 0; > } > > static struct file_system_type autofs_fs_type = { > diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c > index db4117e..be89fd2 100644 > --- a/fs/autofs4/root.c > +++ b/fs/autofs4/root.c > @@ -215,11 +215,24 @@ static void *autofs4_follow_link(struct dentry *dentry, > struct nameidata *nd) > struct autofs_info *ino = autofs4_dentry_ino(dentry); > int oz_mode = autofs4_oz_mode(sbi); > unsigned int lookup_type; > + struct vfsmount *mnt; > int status; > > DPRINTK("dentry=%p %.*s oz_mode=%d nd->flags=%d", > dentry, dentry->d_name.len, dentry->d_name.name, oz_mode, > nd->flags); > + > + mnt = lookup_mount(nd->path.mnt, sbi->mountpoint); > + if (!mnt) { > + status = -ENOENT; > + goto out_error; > + } > + > + dput(nd->path.dentry); > + mntput(nd->path.mnt); > + nd->path.mnt = mnt; > + nd->path.dentry = dget(dentry); > + > /* > * For an expire of a covered direct or offset mount we need > * to break out of follow_down() at the autofs mount trigger > diff --git a/fs/namei.c b/fs/namei.c > index 868d0cb..69a78ee 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -539,11 +539,8 @@ __do_follow_link(struct path *path, struct nameidata > *nd, void **p) > touch_atime(path->mnt, dentry); > nd_set_link(nd, NULL); > > - if (path->mnt != nd->path.mnt) { > - path_to_nameidata(path, nd); > - dget(dentry); > - } > - mntget(path->mnt); > + if (path->mnt == nd->path.mnt) > + mntget(nd->path.mnt); > nd->last_type = LAST_BIND; > *p = dentry->d_inode->i_op->follow_link(dentry, nd); > error = PTR_ERR(*p); > diff --git a/fs/namespace.c b/fs/namespace.c > index 88058de..19b7fc9 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -445,6 +445,7 @@ struct vfsmount *lookup_mnt(struct path *path) > spin_unlock(&vfsmount_lock); > return child_mnt; > } > +EXPORT_SYMBOL_GPL(lookup_mnt); > > static inline int check_mnt(struct vfsmount *mnt) > { > > > _______________________________________________ autofs mailing list [email protected] http://linux.kernel.org/mailman/listinfo/autofs
