Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754885Ab0HHQAE (ORCPT ); Sun, 8 Aug 2010 12:00:04 -0400 Received: from mx1.redhat.com ([209.132.183.28]:6910 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754778Ab0HHPzI (ORCPT ); Sun, 8 Aug 2010 11:55:08 -0400 From: Valerie Aurora To: Alexander Viro Cc: Miklos Szeredi , Jan Blunck , Christoph Hellwig , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Valerie Aurora Subject: [PATCH 18/39] union-mount: Support for union mounting file systems Date: Sun, 8 Aug 2010 11:52:35 -0400 Message-Id: <1281282776-5447-19-git-send-email-vaurora@redhat.com> In-Reply-To: <1281282776-5447-1-git-send-email-vaurora@redhat.com> References: <1281282776-5447-1-git-send-email-vaurora@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 11611 Lines: 396 Create and tear down union mount structures on mount. Check requirements for union mounts. This version clones the read-only mounts as one big tree and points to them from the superblock of the topmost layer file system. Thanks to Felix Fietkau for a bug fix and Miklos Szeredi for better mount error messages. Signed-off-by: Valerie Aurora --- fs/namespace.c | 255 ++++++++++++++++++++++++++++++++++++++++++++++++- fs/super.c | 1 + include/linux/fs.h | 7 ++ include/linux/mount.h | 2 + 4 files changed, 263 insertions(+), 2 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index f115cb6..aa6a132 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -33,6 +33,7 @@ #include #include "pnode.h" #include "internal.h" +#include "union.h" #define HASH_SHIFT ilog2(PAGE_SIZE / sizeof(struct list_head)) #define HASH_SIZE (1UL << HASH_SHIFT) @@ -1050,6 +1051,7 @@ void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill) propagate_umount(kill); list_for_each_entry(p, kill, mnt_hash) { + d_free_unions(p->mnt_root); list_del_init(&p->mnt_expire); list_del_init(&p->mnt_list); __touch_mnt_namespace(p->mnt_ns); @@ -1333,6 +1335,217 @@ static int invent_group_ids(struct vfsmount *mnt, bool recurse) return 0; } +/** + * check_mnt_union - mount-time checks for union mount + * + * @mntpnt: path of the mountpoint the new mount will be on + * @topmost_mnt: vfsmount of the new file system to be mounted + * @mnt_flags: mount flags for the new file system + * + * Mount-time check of upper and lower layer file systems to see if we + * can union mount one on the other. + * + * The rules: + * + * Lower layer(s) and submounts read-only: We can't deal with + * namespace changes in the lower layers of a union, so the lower + * layer must be read-only. Note that we could possibly convert a + * read-write unioned mount into a read-only mount here. + * + * Lower layer(s) and submounts not shared: The lower layer(s) of a + * union mount must not have any changes to its namespace. Therefore, + * it must not be part of any mount event propagation group - i.e., + * shared or slave. + * + * Union only at roots of file systems: Only permit unioning of file + * systems at their root directories. This allows us to mark entire + * mounts as unioned. Otherwise we must slowly and expensively work + * our way up a path looking for a unioned directory before we know if + * a path is from a unioned lower layer. + * + * Topmost layer must be writable to support our readdir() + * solution of copying up all lower level entries to the + * topmost layer. + * + * Topmost file system must support whiteouts and fallthrus. + * + * Topmost file system can't be mounted elsewhere. XXX implement some + * kind of marker in the superblock so subsequent mounts are not + * possible. + * + */ + +static int +check_mnt_union(struct path *mntpnt, struct vfsmount *topmost_mnt, int mnt_flags) +{ + struct vfsmount *p, *lower_mnt = mntpnt->mnt; + + if (!(mnt_flags & MNT_UNION)) + return 0; + +#ifndef CONFIG_UNION_MOUNT + printk(KERN_INFO "union mount: not supported by the kernel\n"); + return -EINVAL; +#endif + for (p = lower_mnt; p; p = next_mnt(p, lower_mnt)) { + if (!(p->mnt_sb->s_flags & MS_RDONLY)) + return -EBUSY; + if (IS_MNT_SHARED(p) || IS_MNT_SLAVE(p)) + return -EBUSY; + } + + if (!IS_ROOT(mntpnt->dentry)) { + printk(KERN_INFO "union mount: mount point must be a root dir\n"); + return -EINVAL; + } + + if (mnt_flags & MNT_READONLY) + return -EROFS; + + if (!(topmost_mnt->mnt_sb->s_flags & MS_WHITEOUT)) { + printk(KERN_INFO "union mount: whiteouts not supported by fs\n"); + return -EINVAL; + } + + if (!(topmost_mnt->mnt_sb->s_flags & MS_FALLTHRU)) { + printk(KERN_INFO "union mount: fallthrus not supported by fs\n"); + return -EINVAL; + } + + /* XXX top level mount should only be mounted once */ + + return 0; +} + +void put_union_sb(struct super_block *sb) +{ + struct vfsmount *p, *mnt; + LIST_HEAD(umount_list); + + if (!sb->s_ro_union_mnts) + return; + mnt = sb->s_ro_union_mnts; + for (p = mnt; p; p = next_mnt(p, mnt)) + dec_hard_readonly_users(p); + spin_lock(&vfsmount_lock); + umount_tree(mnt, 0, &umount_list); + spin_unlock(&vfsmount_lock); + release_mounts(&umount_list); +} + +static void cleanup_mnt_union(struct vfsmount *topmost_mnt) +{ + d_free_unions(topmost_mnt->mnt_root); + put_union_sb(topmost_mnt->mnt_sb); +} + +/* + * find_union_root - Find the "lowest" (union low) mount to be unioned + */ + +static struct vfsmount *find_union_root(struct vfsmount *topmost_mnt, struct path *mntpnt) +{ + struct path this_layer = *mntpnt; + struct vfsmount *lowest_mnt = NULL; + + while(check_mnt_union(&this_layer, topmost_mnt, MNT_UNION) == 0) { + lowest_mnt = this_layer.mnt; + this_layer.dentry = this_layer.mnt->mnt_mountpoint; + this_layer.mnt = this_layer.mnt->mnt_parent; + } + return lowest_mnt; +} + +/* + * Build the union stack for the root dir. Note that topmost_mnt is + * not connected to the mount tree yet and that the cloned tree is not + * either. + */ + +static int build_root_union(struct vfsmount *topmost_mnt, struct vfsmount *clone_root) +{ + struct union_dir **next_ud; + struct path upper, lower; + struct vfsmount *p, *mnt; + int err = 0; + + /* + * Find the topmost read-only mount, starting from the root + * of the cloned tree of read-only mounts. __lookup_mnt() and + * friends don't work because the cloned tree is not mounted + * anywhere. + */ + mnt = clone_root; + for (p = clone_root; p; p = next_mnt(p, clone_root)) { + if ((p->mnt_parent == mnt) && + (p->mnt_mountpoint == mnt->mnt_root)) + mnt = p; + } + + /* Build the root union stack */ + upper.mnt = topmost_mnt; + upper.dentry = topmost_mnt->mnt_root; + next_ud = &upper.dentry->d_union_dir; + + while (upper.mnt != clone_root) { + lower.mnt = mntget(mnt); + lower.dentry = dget(mnt->mnt_root); + err = union_add_dir(&upper, &lower, next_ud); + if (err) + goto out; + next_ud = &(*next_ud)->u_lower; + upper = lower; + mnt = mnt->mnt_parent; + } +out: + return err; +} + +/** + * prepare_mnt_union - do setup necessary for a union mount + * + * @topmost_mnt: vfsmount of topmost layer + * @mntpnt: path of requested mountpoint + * + * We union every underlying file system that is mounted on the same + * mountpoint (well, pathname), read-only, and not shared. We clone + * the entire underlying read-only mount tree and keep a pointer to it + * from the topmost file system's superblock. + * + * XXX - Maybe should take # of layers to go down as an argument. But + * how to pass this in through mount options? All solutions look ugly. + */ + +static int prepare_mnt_union(struct vfsmount *topmost_mnt, struct path *mntpnt) +{ + struct super_block *sb = topmost_mnt->mnt_sb; + struct vfsmount *p, *clone_root; + int err; + + clone_root = find_union_root(topmost_mnt, mntpnt); + if (!clone_root) + return 0; /* Nothing to union */ + + /* Clone the whole mount tree that we're going to union. */ + err = -ENOMEM; + sb->s_ro_union_mnts = copy_tree(clone_root, clone_root->mnt_root, + CL_COPY_ALL | CL_PRIVATE); + if (!sb->s_ro_union_mnts) + goto out; + + for (p = sb->s_ro_union_mnts; p; p = next_mnt(p, sb->s_ro_union_mnts)) + inc_hard_readonly_users(p); + + err = build_root_union(topmost_mnt, clone_root); + if (err) + goto out; + + return 0; +out: + cleanup_mnt_union(topmost_mnt); + return err; +} + /* * @source_mnt : mount tree to be attached * @nd : place the mount tree @source_mnt is attached @@ -1410,9 +1623,16 @@ static int attach_recursive_mnt(struct vfsmount *source_mnt, if (err) goto out; } + + if (!parent_path && IS_MNT_UNION(source_mnt)) { + err = prepare_mnt_union(source_mnt, path); + if (err) + goto out_cleanup_ids; + } + err = propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list); if (err) - goto out_cleanup_ids; + goto out_cleanup_union; spin_lock(&vfsmount_lock); @@ -1436,6 +1656,9 @@ static int attach_recursive_mnt(struct vfsmount *source_mnt, spin_unlock(&vfsmount_lock); return 0; + out_cleanup_union: + if (IS_MNT_UNION(source_mnt)) + cleanup_mnt_union(source_mnt); out_cleanup_ids: if (IS_MNT_SHARED(dest_mnt)) cleanup_group_ids(source_mnt, NULL); @@ -1482,6 +1705,17 @@ static int do_change_type(struct path *path, int flag) return -EINVAL; down_write(&namespace_sem); + + /* + * Mounts of file systems with read-only users can't deal with + * mount/umount propagation events - it's the moral equivalent + * of rm -rf dir/ or the like. + */ + if (sb_is_hard_readonly(mnt->mnt_sb)) { + err = -EROFS; + goto out_unlock; + } + if (type == MS_SHARED) { err = invent_group_ids(mnt, recurse); if (err) @@ -1519,6 +1753,9 @@ static int do_loopback(struct path *path, char *old_name, err = -EINVAL; if (IS_MNT_UNBINDABLE(old_path.mnt)) goto out; + /* Mount part of a union mount elsewhere? The mind boggles. */ + if (IS_MNT_UNION(old_path.mnt)) + goto out; if (!check_mnt(path->mnt) || !check_mnt(old_path.mnt)) goto out; @@ -1540,7 +1777,6 @@ static int do_loopback(struct path *path, char *old_name, spin_unlock(&vfsmount_lock); release_mounts(&umount_list); } - out: up_write(&namespace_sem); path_put(&old_path); @@ -1581,6 +1817,17 @@ static int do_remount(struct path *path, int flags, int mnt_flags, if (!check_mnt(path->mnt)) return -EINVAL; + if (mnt_flags & MNT_UNION) + return -EINVAL; + + if ((path->mnt->mnt_flags & MNT_UNION) && + !(mnt_flags & MNT_UNION)) + return -EINVAL; + + if ((path->mnt->mnt_flags & MNT_UNION) && + (mnt_flags & MNT_READONLY)) + return -EINVAL; + if (path->dentry != path->mnt->mnt_root) return -EINVAL; @@ -1743,6 +1990,10 @@ int do_add_mount(struct vfsmount *newmnt, struct path *path, if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode)) goto unlock; + err = check_mnt_union(path, newmnt, mnt_flags); + if (err) + goto unlock; + newmnt->mnt_flags = mnt_flags; if ((err = graft_tree(newmnt, path))) goto unlock; diff --git a/fs/super.c b/fs/super.c index 86bdf1f..bdfe98f 100644 --- a/fs/super.c +++ b/fs/super.c @@ -160,6 +160,7 @@ void deactivate_locked_super(struct super_block *s) if (atomic_dec_and_test(&s->s_active)) { fs->kill_sb(s); put_filesystem(fs); + put_union_sb(s); put_super(s); } else { up_write(&s->s_umount); diff --git a/include/linux/fs.h b/include/linux/fs.h index 31cfa48..b88d088 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1397,6 +1397,13 @@ struct super_block { * read-only. */ int s_hard_readonly_users; + + /* + * If this is the topmost file system in a union mount, this + * points to the root of the private cloned vfsmount tree of + * the read-only mounts in this union. + */ + struct vfsmount *s_ro_union_mnts; }; extern struct timespec current_fs_time(struct super_block *sb); diff --git a/include/linux/mount.h b/include/linux/mount.h index 0302703..17d3d27 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -136,4 +136,6 @@ extern void mark_mounts_for_expiry(struct list_head *mounts); extern dev_t name_to_dev_t(char *name); +extern void put_union_sb(struct super_block *sb); + #endif /* _LINUX_MOUNT_H */ -- 1.6.3.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/