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[PATCH] shared mount handling: bind and rbind

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Implement handling of MS_BIND in presense of shared mounts (see
Documentation/sharedsubtree.txt in the end of patch series for detailed
description).

Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Ram Pai 2005-11-07 17:19:50 -05:00 committed by Linus Torvalds
parent 03e06e68ff
commit b90fa9ae8f
4 changed files with 204 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

126
fs/namespace.c
View File

@ -28,8 +28,6 @@
extern int __init init_rootfs(void);
#define CL_EXPIRE 0x01
#ifdef CONFIG_SYSFS
extern int __init sysfs_init(void);
#else
@ -145,13 +143,43 @@ static void detach_mnt(struct vfsmount *mnt, struct nameidata *old_nd)
old_nd->dentry->d_mounted--;
}
void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry,
struct vfsmount *child_mnt)
{
child_mnt->mnt_parent = mntget(mnt);
child_mnt->mnt_mountpoint = dget(dentry);
dentry->d_mounted++;
}
static void attach_mnt(struct vfsmount *mnt, struct nameidata *nd)
{
mnt->mnt_parent = mntget(nd->mnt);
mnt->mnt_mountpoint = dget(nd->dentry);
list_add(&mnt->mnt_hash, mount_hashtable + hash(nd->mnt, nd->dentry));
mnt_set_mountpoint(nd->mnt, nd->dentry, mnt);
list_add_tail(&mnt->mnt_hash, mount_hashtable +
hash(nd->mnt, nd->dentry));
list_add_tail(&mnt->mnt_child, &nd->mnt->mnt_mounts);
nd->dentry->d_mounted++;
}
/*
* the caller must hold vfsmount_lock
*/
static void commit_tree(struct vfsmount *mnt)
{
struct vfsmount *parent = mnt->mnt_parent;
struct vfsmount *m;
LIST_HEAD(head);
struct namespace *n = parent->mnt_namespace;
BUG_ON(parent == mnt);
list_add_tail(&head, &mnt->mnt_list);
list_for_each_entry(m, &head, mnt_list)
m->mnt_namespace = n;
list_splice(&head, n->list.prev);
list_add_tail(&mnt->mnt_hash, mount_hashtable +
hash(parent, mnt->mnt_mountpoint));
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
touch_namespace(n);
}
static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
@ -183,7 +211,11 @@ static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
mnt->mnt_root = dget(root);
mnt->mnt_mountpoint = mnt->mnt_root;
mnt->mnt_parent = mnt;
mnt->mnt_namespace = current->namespace;
if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
list_add(&mnt->mnt_share, &old->mnt_share);
if (flag & CL_MAKE_SHARED)
set_mnt_shared(mnt);
/* stick the duplicate mount on the same expiry list
* as the original if that was on one */
@ -379,7 +411,7 @@ int may_umount(struct vfsmount *mnt)
EXPORT_SYMBOL(may_umount);
static void release_mounts(struct list_head *head)
void release_mounts(struct list_head *head)
{
struct vfsmount *mnt;
while(!list_empty(head)) {
@ -401,7 +433,7 @@ static void release_mounts(struct list_head *head)
}
}
static void umount_tree(struct vfsmount *mnt, struct list_head *kill)
void umount_tree(struct vfsmount *mnt, struct list_head *kill)
{
struct vfsmount *p;
@ -581,7 +613,7 @@ static int lives_below_in_same_fs(struct dentry *d, struct dentry *dentry)
}
}
static struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
int flag)
{
struct vfsmount *res, *p, *q, *r, *s;
@ -626,6 +658,67 @@ Enomem:
return NULL;
}
/*
* @source_mnt : mount tree to be attached
* @nd : place the mount tree @source_mnt is attached
*
* NOTE: in the table below explains the semantics when a source mount
* of a given type is attached to a destination mount of a given type.
* ---------------------------------------------
* | BIND MOUNT OPERATION |
* |********************************************
* | source-->| shared | private |
* | dest | | |
* | | | | |
* | v | | |
* |********************************************
* | shared | shared (++) | shared (+) |
* | | | |
* |non-shared| shared (+) | private |
* *********************************************
* A bind operation clones the source mount and mounts the clone on the
* destination mount.
*
* (++) the cloned mount is propagated to all the mounts in the propagation
* tree of the destination mount and the cloned mount is added to
* the peer group of the source mount.
* (+) the cloned mount is created under the destination mount and is marked
* as shared. The cloned mount is added to the peer group of the source
* mount.
*
* if the source mount is a tree, the operations explained above is
* applied to each mount in the tree.
* Must be called without spinlocks held, since this function can sleep
* in allocations.
*/
static int attach_recursive_mnt(struct vfsmount *source_mnt,
struct nameidata *nd)
{
LIST_HEAD(tree_list);
struct vfsmount *dest_mnt = nd->mnt;
struct dentry *dest_dentry = nd->dentry;
struct vfsmount *child, *p;
if (propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list))
return -EINVAL;
if (IS_MNT_SHARED(dest_mnt)) {
for (p = source_mnt; p; p = next_mnt(p, source_mnt))
set_mnt_shared(p);
}
spin_lock(&vfsmount_lock);
mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt);
commit_tree(source_mnt);
list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
list_del_init(&child->mnt_hash);
commit_tree(child);
}
spin_unlock(&vfsmount_lock);
return 0;
}
static int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
{
int err;
@ -646,17 +739,8 @@ static int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
goto out_unlock;
err = -ENOENT;
spin_lock(&vfsmount_lock);
if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry)) {
struct list_head head;
attach_mnt(mnt, nd);
list_add_tail(&head, &mnt->mnt_list);
list_splice(&head, current->namespace->list.prev);
err = 0;
touch_namespace(current->namespace);
}
spin_unlock(&vfsmount_lock);
if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry))
err = attach_recursive_mnt(mnt, nd);
out_unlock:
up(&nd->dentry->d_inode->i_sem);
if (!err)

81
fs/pnode.c
View File

@ -20,9 +20,88 @@ static inline struct vfsmount *next_peer(struct vfsmount *p)
void change_mnt_propagation(struct vfsmount *mnt, int type)
{
if (type == MS_SHARED) {
mnt->mnt_flags |= MNT_SHARED;
set_mnt_shared(mnt);
} else {
list_del_init(&mnt->mnt_share);
mnt->mnt_flags &= ~MNT_PNODE_MASK;
}
}
/*
* get the next mount in the propagation tree.
* @m: the mount seen last
* @origin: the original mount from where the tree walk initiated
*/
static struct vfsmount *propagation_next(struct vfsmount *m,
struct vfsmount *origin)
{
m = next_peer(m);
if (m == origin)
return NULL;
return m;
}
/*
* mount 'source_mnt' under the destination 'dest_mnt' at
* dentry 'dest_dentry'. And propagate that mount to
* all the peer and slave mounts of 'dest_mnt'.
* Link all the new mounts into a propagation tree headed at
* source_mnt. Also link all the new mounts using ->mnt_list
* headed at source_mnt's ->mnt_list
*
* @dest_mnt: destination mount.
* @dest_dentry: destination dentry.
* @source_mnt: source mount.
* @tree_list : list of heads of trees to be attached.
*/
int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
struct vfsmount *source_mnt, struct list_head *tree_list)
{
struct vfsmount *m, *child;
int ret = 0;
struct vfsmount *prev_dest_mnt = dest_mnt;
struct vfsmount *prev_src_mnt = source_mnt;
LIST_HEAD(tmp_list);
LIST_HEAD(umount_list);
for (m = propagation_next(dest_mnt, dest_mnt); m;
m = propagation_next(m, dest_mnt)) {
int type = CL_PROPAGATION;
if (IS_MNT_NEW(m))
continue;
if (IS_MNT_SHARED(m))
type |= CL_MAKE_SHARED;
if (!(child = copy_tree(source_mnt, source_mnt->mnt_root,
type))) {
ret = -ENOMEM;
list_splice(tree_list, tmp_list.prev);
goto out;
}
if (is_subdir(dest_dentry, m->mnt_root)) {
mnt_set_mountpoint(m, dest_dentry, child);
list_add_tail(&child->mnt_hash, tree_list);
} else {
/*
* This can happen if the parent mount was bind mounted
* on some subdirectory of a shared/slave mount.
*/
list_add_tail(&child->mnt_hash, &tmp_list);
}
prev_dest_mnt = m;
prev_src_mnt = child;
}
out:
spin_lock(&vfsmount_lock);
while (!list_empty(&tmp_list)) {
child = list_entry(tmp_list.next, struct vfsmount, mnt_hash);
list_del_init(&child->mnt_hash);
umount_tree(child, &umount_list);
}
spin_unlock(&vfsmount_lock);
release_mounts(&umount_list);
return ret;
}

14
fs/pnode.h
View File

@ -12,7 +12,21 @@
#include <linux/mount.h>
#define IS_MNT_SHARED(mnt) (mnt->mnt_flags & MNT_SHARED)
#define IS_MNT_NEW(mnt) (!mnt->mnt_namespace)
#define CLEAR_MNT_SHARED(mnt) (mnt->mnt_flags &= ~MNT_SHARED)
#define CL_EXPIRE 0x01
#define CL_COPY_ALL 0x04
#define CL_MAKE_SHARED 0x08
#define CL_PROPAGATION 0x10
static inline void set_mnt_shared(struct vfsmount *mnt)
{
mnt->mnt_flags &= ~MNT_PNODE_MASK;
mnt->mnt_flags |= MNT_SHARED;
}
void change_mnt_propagation(struct vfsmount *, int);
int propagate_mnt(struct vfsmount *, struct dentry *, struct vfsmount *,
struct list_head *);
#endif /* _LINUX_PNODE_H */

5
include/linux/fs.h
View File

@ -1251,7 +1251,12 @@ extern int unregister_filesystem(struct file_system_type *);
extern struct vfsmount *kern_mount(struct file_system_type *);
extern int may_umount_tree(struct vfsmount *);
extern int may_umount(struct vfsmount *);
extern void umount_tree(struct vfsmount *, struct list_head *);
extern void release_mounts(struct list_head *);
extern long do_mount(char *, char *, char *, unsigned long, void *);
extern struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int);
extern void mnt_set_mountpoint(struct vfsmount *, struct dentry *,
struct vfsmount *);
extern int vfs_statfs(struct super_block *, struct kstatfs *);