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Ram PaiLinus Torvalds
Ram Pai
authored and
Linus Torvalds
committed
[PATCH] shared mount handling: bind and rbind
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 <[email protected]> Signed-off-by: Al Viro <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
1 parent 03e06e6 commit b90fa9a

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4 files changed

+204
-22
lines changed

4 files changed

+204
-22
lines changed

‎fs/namespace.c

Lines changed: 105 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -28,8 +28,6 @@
2828

2929
extern int __init init_rootfs(void);
3030

31-
#define CL_EXPIRE 0x01
32-
3331
#ifdef CONFIG_SYSFS
3432
extern int __init sysfs_init(void);
3533
#else
@@ -145,13 +143,43 @@ static void detach_mnt(struct vfsmount *mnt, struct nameidata *old_nd)
145143
old_nd->dentry->d_mounted--;
146144
}
147145

146+
void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry,
147+
struct vfsmount *child_mnt)
148+
{
149+
child_mnt->mnt_parent = mntget(mnt);
150+
child_mnt->mnt_mountpoint = dget(dentry);
151+
dentry->d_mounted++;
152+
}
153+
148154
static void attach_mnt(struct vfsmount *mnt, struct nameidata *nd)
149155
{
150-
mnt->mnt_parent = mntget(nd->mnt);
151-
mnt->mnt_mountpoint = dget(nd->dentry);
152-
list_add(&mnt->mnt_hash, mount_hashtable + hash(nd->mnt, nd->dentry));
156+
mnt_set_mountpoint(nd->mnt, nd->dentry, mnt);
157+
list_add_tail(&mnt->mnt_hash, mount_hashtable +
158+
hash(nd->mnt, nd->dentry));
153159
list_add_tail(&mnt->mnt_child, &nd->mnt->mnt_mounts);
154-
nd->dentry->d_mounted++;
160+
}
161+
162+
/*
163+
* the caller must hold vfsmount_lock
164+
*/
165+
static void commit_tree(struct vfsmount *mnt)
166+
{
167+
struct vfsmount *parent = mnt->mnt_parent;
168+
struct vfsmount *m;
169+
LIST_HEAD(head);
170+
struct namespace *n = parent->mnt_namespace;
171+
172+
BUG_ON(parent == mnt);
173+
174+
list_add_tail(&head, &mnt->mnt_list);
175+
list_for_each_entry(m, &head, mnt_list)
176+
m->mnt_namespace = n;
177+
list_splice(&head, n->list.prev);
178+
179+
list_add_tail(&mnt->mnt_hash, mount_hashtable +
180+
hash(parent, mnt->mnt_mountpoint));
181+
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
182+
touch_namespace(n);
155183
}
156184

157185
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,
183211
mnt->mnt_root = dget(root);
184212
mnt->mnt_mountpoint = mnt->mnt_root;
185213
mnt->mnt_parent = mnt;
186-
mnt->mnt_namespace = current->namespace;
214+
215+
if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
216+
list_add(&mnt->mnt_share, &old->mnt_share);
217+
if (flag & CL_MAKE_SHARED)
218+
set_mnt_shared(mnt);
187219

188220
/* stick the duplicate mount on the same expiry list
189221
* as the original if that was on one */
@@ -379,7 +411,7 @@ int may_umount(struct vfsmount *mnt)
379411

380412
EXPORT_SYMBOL(may_umount);
381413

382-
static void release_mounts(struct list_head *head)
414+
void release_mounts(struct list_head *head)
383415
{
384416
struct vfsmount *mnt;
385417
while(!list_empty(head)) {
@@ -401,7 +433,7 @@ static void release_mounts(struct list_head *head)
401433
}
402434
}
403435

404-
static void umount_tree(struct vfsmount *mnt, struct list_head *kill)
436+
void umount_tree(struct vfsmount *mnt, struct list_head *kill)
405437
{
406438
struct vfsmount *p;
407439

@@ -581,7 +613,7 @@ static int lives_below_in_same_fs(struct dentry *d, struct dentry *dentry)
581613
}
582614
}
583615

584-
static struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
616+
struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
585617
int flag)
586618
{
587619
struct vfsmount *res, *p, *q, *r, *s;
@@ -626,6 +658,67 @@ static struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
626658
return NULL;
627659
}
628660

661+
/*
662+
* @source_mnt : mount tree to be attached
663+
* @nd : place the mount tree @source_mnt is attached
664+
*
665+
* NOTE: in the table below explains the semantics when a source mount
666+
* of a given type is attached to a destination mount of a given type.
667+
* ---------------------------------------------
668+
* | BIND MOUNT OPERATION |
669+
* |********************************************
670+
* | source-->| shared | private |
671+
* | dest | | |
672+
* | | | | |
673+
* | v | | |
674+
* |********************************************
675+
* | shared | shared (++) | shared (+) |
676+
* | | | |
677+
* |non-shared| shared (+) | private |
678+
* *********************************************
679+
* A bind operation clones the source mount and mounts the clone on the
680+
* destination mount.
681+
*
682+
* (++) the cloned mount is propagated to all the mounts in the propagation
683+
* tree of the destination mount and the cloned mount is added to
684+
* the peer group of the source mount.
685+
* (+) the cloned mount is created under the destination mount and is marked
686+
* as shared. The cloned mount is added to the peer group of the source
687+
* mount.
688+
*
689+
* if the source mount is a tree, the operations explained above is
690+
* applied to each mount in the tree.
691+
* Must be called without spinlocks held, since this function can sleep
692+
* in allocations.
693+
*/
694+
static int attach_recursive_mnt(struct vfsmount *source_mnt,
695+
struct nameidata *nd)
696+
{
697+
LIST_HEAD(tree_list);
698+
struct vfsmount *dest_mnt = nd->mnt;
699+
struct dentry *dest_dentry = nd->dentry;
700+
struct vfsmount *child, *p;
701+
702+
if (propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list))
703+
return -EINVAL;
704+
705+
if (IS_MNT_SHARED(dest_mnt)) {
706+
for (p = source_mnt; p; p = next_mnt(p, source_mnt))
707+
set_mnt_shared(p);
708+
}
709+
710+
spin_lock(&vfsmount_lock);
711+
mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt);
712+
commit_tree(source_mnt);
713+
714+
list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
715+
list_del_init(&child->mnt_hash);
716+
commit_tree(child);
717+
}
718+
spin_unlock(&vfsmount_lock);
719+
return 0;
720+
}
721+
629722
static int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
630723
{
631724
int err;
@@ -646,17 +739,8 @@ static int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
646739
goto out_unlock;
647740

648741
err = -ENOENT;
649-
spin_lock(&vfsmount_lock);
650-
if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry)) {
651-
struct list_head head;
652-
653-
attach_mnt(mnt, nd);
654-
list_add_tail(&head, &mnt->mnt_list);
655-
list_splice(&head, current->namespace->list.prev);
656-
err = 0;
657-
touch_namespace(current->namespace);
658-
}
659-
spin_unlock(&vfsmount_lock);
742+
if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry))
743+
err = attach_recursive_mnt(mnt, nd);
660744
out_unlock:
661745
up(&nd->dentry->d_inode->i_sem);
662746
if (!err)

‎fs/pnode.c

Lines changed: 80 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -20,9 +20,88 @@ static inline struct vfsmount *next_peer(struct vfsmount *p)
2020
void change_mnt_propagation(struct vfsmount *mnt, int type)
2121
{
2222
if (type == MS_SHARED) {
23-
mnt->mnt_flags |= MNT_SHARED;
23+
set_mnt_shared(mnt);
2424
} else {
2525
list_del_init(&mnt->mnt_share);
2626
mnt->mnt_flags &= ~MNT_PNODE_MASK;
2727
}
2828
}
29+
30+
/*
31+
* get the next mount in the propagation tree.
32+
* @m: the mount seen last
33+
* @origin: the original mount from where the tree walk initiated
34+
*/
35+
static struct vfsmount *propagation_next(struct vfsmount *m,
36+
struct vfsmount *origin)
37+
{
38+
m = next_peer(m);
39+
if (m == origin)
40+
return NULL;
41+
return m;
42+
}
43+
44+
/*
45+
* mount 'source_mnt' under the destination 'dest_mnt' at
46+
* dentry 'dest_dentry'. And propagate that mount to
47+
* all the peer and slave mounts of 'dest_mnt'.
48+
* Link all the new mounts into a propagation tree headed at
49+
* source_mnt. Also link all the new mounts using ->mnt_list
50+
* headed at source_mnt's ->mnt_list
51+
*
52+
* @dest_mnt: destination mount.
53+
* @dest_dentry: destination dentry.
54+
* @source_mnt: source mount.
55+
* @tree_list : list of heads of trees to be attached.
56+
*/
57+
int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
58+
struct vfsmount *source_mnt, struct list_head *tree_list)
59+
{
60+
struct vfsmount *m, *child;
61+
int ret = 0;
62+
struct vfsmount *prev_dest_mnt = dest_mnt;
63+
struct vfsmount *prev_src_mnt = source_mnt;
64+
LIST_HEAD(tmp_list);
65+
LIST_HEAD(umount_list);
66+
67+
for (m = propagation_next(dest_mnt, dest_mnt); m;
68+
m = propagation_next(m, dest_mnt)) {
69+
int type = CL_PROPAGATION;
70+
71+
if (IS_MNT_NEW(m))
72+
continue;
73+
74+
if (IS_MNT_SHARED(m))
75+
type |= CL_MAKE_SHARED;
76+
77+
if (!(child = copy_tree(source_mnt, source_mnt->mnt_root,
78+
type))) {
79+
ret = -ENOMEM;
80+
list_splice(tree_list, tmp_list.prev);
81+
goto out;
82+
}
83+
84+
if (is_subdir(dest_dentry, m->mnt_root)) {
85+
mnt_set_mountpoint(m, dest_dentry, child);
86+
list_add_tail(&child->mnt_hash, tree_list);
87+
} else {
88+
/*
89+
* This can happen if the parent mount was bind mounted
90+
* on some subdirectory of a shared/slave mount.
91+
*/
92+
list_add_tail(&child->mnt_hash, &tmp_list);
93+
}
94+
prev_dest_mnt = m;
95+
prev_src_mnt = child;
96+
}
97+
out:
98+
spin_lock(&vfsmount_lock);
99+
while (!list_empty(&tmp_list)) {
100+
child = list_entry(tmp_list.next, struct vfsmount, mnt_hash);
101+
list_del_init(&child->mnt_hash);
102+
umount_tree(child, &umount_list);
103+
}
104+
spin_unlock(&vfsmount_lock);
105+
release_mounts(&umount_list);
106+
return ret;
107+
}

‎fs/pnode.h

Lines changed: 14 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -12,7 +12,21 @@
1212
#include <linux/mount.h>
1313

1414
#define IS_MNT_SHARED(mnt) (mnt->mnt_flags & MNT_SHARED)
15+
#define IS_MNT_NEW(mnt) (!mnt->mnt_namespace)
1516
#define CLEAR_MNT_SHARED(mnt) (mnt->mnt_flags &= ~MNT_SHARED)
1617

18+
#define CL_EXPIRE 0x01
19+
#define CL_COPY_ALL 0x04
20+
#define CL_MAKE_SHARED 0x08
21+
#define CL_PROPAGATION 0x10
22+
23+
static inline void set_mnt_shared(struct vfsmount *mnt)
24+
{
25+
mnt->mnt_flags &= ~MNT_PNODE_MASK;
26+
mnt->mnt_flags |= MNT_SHARED;
27+
}
28+
1729
void change_mnt_propagation(struct vfsmount *, int);
30+
int propagate_mnt(struct vfsmount *, struct dentry *, struct vfsmount *,
31+
struct list_head *);
1832
#endif /* _LINUX_PNODE_H */

‎include/linux/fs.h

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1251,7 +1251,12 @@ extern int unregister_filesystem(struct file_system_type *);
12511251
extern struct vfsmount *kern_mount(struct file_system_type *);
12521252
extern int may_umount_tree(struct vfsmount *);
12531253
extern int may_umount(struct vfsmount *);
1254+
extern void umount_tree(struct vfsmount *, struct list_head *);
1255+
extern void release_mounts(struct list_head *);
12541256
extern long do_mount(char *, char *, char *, unsigned long, void *);
1257+
extern struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int);
1258+
extern void mnt_set_mountpoint(struct vfsmount *, struct dentry *,
1259+
struct vfsmount *);
12551260

12561261
extern int vfs_statfs(struct super_block *, struct kstatfs *);
12571262

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