From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bharata B Rao Subject: [RFC][PATCH 7/14] Union-mount mounting Date: Mon, 14 May 2007 15:11:50 +0530 Message-ID: <20070514094150.GI4139@in.ibm.com> References: <20070514093722.GB4139@in.ibm.com> Reply-To: bharata@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: linux-fsdevel@vger.kernel.org, Jan Blunck To: linux-kernel@vger.kernel.org Return-path: Received: from e31.co.us.ibm.com ([32.97.110.149]:41651 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933862AbXENJeb (ORCPT ); Mon, 14 May 2007 05:34:31 -0400 Content-Disposition: inline In-Reply-To: <20070514093722.GB4139@in.ibm.com> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org =46rom: Jan Blunck Subject: Union-mount mounting Adds union mount support to mount() and umount() system calls. Sets up the union stack during mount and destroys it during unmount. TODO: bind and move mounts aren't yet supported with union mounts. Signed-off-by: Jan Blunck Signed-off-by: Bharata B Rao --- fs/namespace.c | 90 +++++++++++++++++++++++++++++++++++++++++= +++++---- fs/union.c | 71 +++++++++++++++++++++++++++++++++++++++ include/linux/fs.h | 3 + include/linux/union.h | 33 ++++++++++++++++++ 4 files changed, 190 insertions(+), 7 deletions(-) --- a/fs/namespace.c +++ b/fs/namespace.c @@ -169,7 +169,7 @@ void mnt_set_mountpoint(struct vfsmount=20 struct vfsmount *child_mnt) { child_mnt->mnt_parent =3D mntget(mnt); - child_mnt->mnt_mountpoint =3D dget(dentry); + child_mnt->mnt_mountpoint =3D __dget(dentry); dentry->d_mounted++; } =20 @@ -294,6 +294,10 @@ static struct vfsmount *clone_mnt(struct if (!mnt) goto alloc_failed; =20 + /* + * As of now, cloning of union mounted mnt isn't permitted. + */ + BUG_ON(mnt->mnt_flags & MNT_UNION); mnt->mnt_flags =3D old->mnt_flags; atomic_inc(&sb->s_active); mnt->mnt_sb =3D sb; @@ -579,16 +583,20 @@ void release_mounts(struct list_head *he mnt =3D list_first_entry(head, struct vfsmount, mnt_hash); list_del_init(&mnt->mnt_hash); if (mnt->mnt_parent !=3D mnt) { - struct dentry *dentry; - struct vfsmount *m; + struct path old_nd; spin_lock(&vfsmount_lock); - dentry =3D mnt->mnt_mountpoint; - m =3D mnt->mnt_parent; + old_nd.dentry =3D mnt->mnt_mountpoint; + old_nd.mnt =3D mnt->mnt_parent; mnt->mnt_mountpoint =3D mnt->mnt_root; mnt->mnt_parent =3D mnt; + detach_mnt_union(mnt, &old_nd); spin_unlock(&vfsmount_lock); - dput(dentry); - mntput(m); + if (mnt->mnt_flags & MNT_UNION) { + UM_DEBUG("shrink the mountpoint's dcache\n"); + shrink_dcache_sb(old_nd.dentry->d_sb); + } + __dput(old_nd.dentry); + mntput(old_nd.mnt); } mntput(mnt); } @@ -621,6 +629,9 @@ static int do_umount(struct vfsmount *mn struct super_block *sb =3D mnt->mnt_sb; int retval; LIST_HEAD(umount_list); +#ifdef CONFIG_UNION_MOUNT + struct union_info *uinfo =3D NULL; +#endif =20 retval =3D security_sb_umount(mnt, flags); if (retval) @@ -685,6 +696,14 @@ static int do_umount(struct vfsmount *mn } =20 down_write(&namespace_sem); +#ifdef CONFIG_UNION_MOUNT + /* + * Grab a reference to the union_info which gets detached + * from the dentries in release_mounts(). + */ + if (mnt->mnt_flags & MNT_UNION) + uinfo =3D union_lock_and_get(mnt->mnt_root); +#endif spin_lock(&vfsmount_lock); event++; =20 @@ -699,6 +718,15 @@ static int do_umount(struct vfsmount *mn security_sb_umount_busy(mnt); up_write(&namespace_sem); release_mounts(&umount_list); +#ifdef CONFIG_UNION_MOUNT + if (uinfo) { + if (atomic_read(&uinfo->u_count) =3D=3D 1) + /* We are the last user of this union_info */ + union_release(uinfo); + else + union_put_and_unlock(uinfo); + } +#endif return retval; } =20 @@ -941,6 +969,9 @@ static int attach_recursive_mnt(struct v set_mnt_shared(p); } =20 + if (source_mnt->mnt_flags & MNT_UNION) + union_alloc_dentry(nd->dentry); + spin_lock(&vfsmount_lock); if (parent_nd) { detach_mnt(source_mnt, parent_nd); @@ -948,6 +979,7 @@ static int attach_recursive_mnt(struct v touch_mnt_namespace(current->nsproxy->mnt_ns); } else { mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt); + attach_mnt_union(source_mnt, nd); commit_tree(source_mnt); } =20 @@ -956,6 +988,7 @@ static int attach_recursive_mnt(struct v commit_tree(child); } spin_unlock(&vfsmount_lock); + union_unlock(nd->dentry); return 0; } =20 @@ -1003,6 +1036,12 @@ static int do_change_type(struct nameida if (nd->dentry !=3D nd->mnt->mnt_root) return -EINVAL; =20 + /* + * Don't change the type of union mounts + */ + if (nd->mnt->mnt_flags & MNT_UNION) + return -EINVAL; + down_write(&namespace_sem); spin_lock(&vfsmount_lock); for (m =3D mnt; m; m =3D (recurse ? next_mnt(m, mnt) : NULL)) @@ -1031,6 +1070,15 @@ static int do_loopback(struct nameidata=20 if (err) return err; =20 + /* + * bind mounting to or from union mounts is not supported + */ + err =3D -EINVAL; + if (nd->mnt->mnt_flags & MNT_UNION) + goto out_unlocked; + if (old_nd.mnt->mnt_flags & MNT_UNION) + goto out_unlocked; + down_write(&namespace_sem); err =3D -EINVAL; if (IS_MNT_UNBINDABLE(old_nd.mnt)) @@ -1064,6 +1112,7 @@ static int do_loopback(struct nameidata=20 =20 out: up_write(&namespace_sem); +out_unlocked: path_release(&old_nd); return err; } @@ -1125,6 +1174,15 @@ static int do_move_mount(struct nameidat if (err) return err; =20 + /* + * moving to or from a union mount is not supported + */ + err =3D -EINVAL; + if (nd->mnt->mnt_flags & MNT_UNION) + goto exit; + if (old_nd.mnt->mnt_flags & MNT_UNION) + goto exit; + down_write(&namespace_sem); while (d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry)= ) ; @@ -1180,6 +1238,7 @@ out: up_write(&namespace_sem); if (!err) path_release(&parent_nd); +exit: path_release(&old_nd); return err; } @@ -1223,6 +1282,9 @@ static int do_new_mount(struct nameidata if (flags & MS_SETUSER) __set_mnt_user(mnt, current->fsuid); =20 + UM_DEBUG("dentry=3D%s, device=3D%s\n", nd->dentry->d_name.name, + mnt->mnt_devname); + return do_add_mount(mnt, nd, mnt_flags, NULL); =20 out_put_filesystem: @@ -1257,6 +1319,12 @@ int do_add_mount(struct vfsmount *newmnt if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode)) goto unlock; =20 + /* Unions couldn't include shared mounts */ + err =3D -EINVAL; + if ((mnt_flags & MNT_UNION) && + IS_MNT_SHARED(nd->mnt)) + goto unlock; + /* Unions couldn't be writable if the filesystem * doesn't know about whiteouts */ err =3D -ENOTSUPP; @@ -1276,6 +1344,14 @@ int do_add_mount(struct vfsmount *newmnt list_add_tail(&newmnt->mnt_expire, fslist); spin_unlock(&vfsmount_lock); } + + UM_DEBUG("mntpoint->d_count=3D%d/%p\n", + atomic_read(&nd->dentry->d_count), + &nd->dentry->d_count); + UM_DEBUG("mntroot->d_count=3D%d/%p\n", + atomic_read(&newmnt->mnt_root->d_count), + &newmnt->mnt_root->d_count); + up_write(&namespace_sem); return 0; =20 --- a/fs/union.c +++ b/fs/union.c @@ -299,3 +299,74 @@ void __dput_union(struct dentry *dentry) =20 return; } + +void attach_mnt_union(struct vfsmount *mnt, struct nameidata *nd) +{ + struct dentry *tmp; + + if (!(mnt->mnt_flags & MNT_UNION)) + return; + + UM_DEBUG("MNT_UNION set for dentry \"%s\", devname=3D%s\n", + mnt->mnt_root->d_name.name, mnt->mnt_devname); + UM_DEBUG("mountpoint \"%s\", inode=3D%p\n", + nd->dentry->d_name.name, nd->dentry->d_inode); + + spin_lock(&mnt->mnt_root->d_lock); + mnt->mnt_root->d_overlaid =3D __dget(nd->dentry); + mnt->mnt_root->d_topmost =3D NULL; + mnt->mnt_root->d_union =3D union_get(nd->dentry->d_union); + spin_unlock(&mnt->mnt_root->d_lock); + + tmp =3D nd->dentry; + while (tmp) { + tmp->d_topmost =3D mnt->mnt_root; + tmp =3D tmp->d_overlaid; + } +} + +void detach_mnt_union(struct vfsmount *mnt, struct path *path) +{ + struct dentry *tmp; + + if (!(mnt->mnt_flags & MNT_UNION)) + return; + + UM_DEBUG("MNT_UNION set for dentry \"%s\", devname=3D%s\n", + mnt->mnt_root->d_name.name, mnt->mnt_devname); + UM_DEBUG("mountpoint \"%s\", inode=3D%p\n", + path->dentry->d_name.name, path->dentry->d_inode); + BUG_ON(mnt->mnt_root->d_topmost); + + /* put reference to the underlying union stack */ + __dput(mnt->mnt_root->d_overlaid); + spin_lock(&mnt->mnt_root->d_lock); + mnt->mnt_root->d_overlaid =3D NULL; + union_put(mnt->mnt_root->d_union); + mnt->mnt_root->d_union =3D NULL; + spin_unlock(&mnt->mnt_root->d_lock); + + /* rearrange the union stack */ + path->dentry->d_topmost =3D NULL; + tmp =3D path->dentry->d_overlaid; + while (tmp) { + tmp->d_topmost =3D path->dentry; + tmp =3D tmp->d_overlaid; + } + + /* If the mount point is the last component in the union, + * put the reference to the union struct */ + if (!path->dentry->d_overlaid) { + spin_lock(&path->dentry->d_lock); + union_put(path->dentry->d_union); + path->dentry->d_union =3D NULL; + spin_unlock(&path->dentry->d_lock); + } + + /* when we looked up the mountpoint to be unmounted + * we dget() a union-mount dentry struct so we have + * to dput() parts of it by hand before we remove the + * topmost dentry (which is mnt->mnt_root) from the + * union stack */ + __dput(path->dentry); +} --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1984,6 +1984,9 @@ static inline ino_t parent_ino(struct de /* kernel/fork.c */ extern int unshare_files(void); =20 +/* fs/union.c */ +#include + /* Transaction based IO helpers */ =20 /* --- /dev/null +++ b/include/linux/union.h @@ -0,0 +1,33 @@ +/* + * VFS based union mount for Linux + * + * Copyright =A9 2004-2007 IBM Corporation + * Author(s): Jan Blunck (j.blunck@tu-harburg.de) + * + * This program is free software; you can redistribute it and/or modif= y it + * under the terms of the GNU General Public License as published by t= he Free + * Software Foundation; either version 2 of the License, or (at your o= ption) + * any later version. + * + */ +#ifndef __LINUX_UNION_H +#define __LINUX_UNION_H +#ifdef __KERNEL__ + +#ifdef CONFIG_UNION_MOUNT + +#include + +/* namespace stuff used at mount time */ +extern void attach_mnt_union(struct vfsmount *, struct nameidata *); +extern void detach_mnt_union(struct vfsmount *, struct path *); + +#else /* CONFIG_UNION_MOUNT */ + +#define attach_mnt_union(mnt,nd) do { /* empty */ } while (0) +#define detach_mnt_union(mnt,nd) do { /* empty */ } while (0) + +#endif /* CONFIG_UNION_MOUNT */ + +#endif /* __KERNEL __ */ +#endif /* __LINUX_UNION_H */ - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel= " in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html