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[PATCH] handling of slave mounts
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This makes bind, rbind, move, clone namespace and umount operations
aware of the semantics of slave mount (see Documentation/sharedsubtree.txt
in the last patch of the 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>
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Ram Pai authored and Linus Torvalds committed Nov 8, 2005
1 parent a58b0eb commit 5afe002
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Showing 2 changed files with 121 additions and 37 deletions.
77 changes: 49 additions & 28 deletions fs/namespace.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -227,8 +227,17 @@ static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
mnt->mnt_mountpoint = mnt->mnt_root;
mnt->mnt_parent = mnt;

if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
list_add(&mnt->mnt_share, &old->mnt_share);
if (flag & CL_SLAVE) {
list_add(&mnt->mnt_slave, &old->mnt_slave_list);
mnt->mnt_master = old;
CLEAR_MNT_SHARED(mnt);
} else {
if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
list_add(&mnt->mnt_share, &old->mnt_share);
if (IS_MNT_SLAVE(old))
list_add(&mnt->mnt_slave, &old->mnt_slave);
mnt->mnt_master = old->mnt_master;
}
if (flag & CL_MAKE_SHARED)
set_mnt_shared(mnt);

Expand Down Expand Up @@ -689,18 +698,18 @@ struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
*
* 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 |
* *********************************************
* -------------------------------------------------------------
* | BIND MOUNT OPERATION |
* |*************************************************************
* | source-->| shared | private | slave |
* | dest | | | |
* | | | | | |
* | v | | | |
* |*************************************************************
* | shared | shared (++) | shared (+) | shared(+++)|
* | | | | |
* |non-shared| shared (+) | private | slave (*) |
* **************************************************************
* A bind operation clones the source mount and mounts the clone on the
* destination mount.
*
Expand All @@ -710,21 +719,33 @@ struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
* (+) 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.
* ---------------------------------------------
* | MOVE MOUNT OPERATION |
* |********************************************
* | source-->| shared | private |
* | dest | | |
* | | | | |
* | v | | |
* |********************************************
* | shared | shared (+) | shared (+) |
* | | | |
* |non-shared| shared (+*) | private |
* *********************************************
* (+) the mount is moved to the destination. And is then propagated to all
* the mounts in the propagation tree of the destination mount.
* (+++) the mount is propagated to all the mounts in the propagation tree
* of the destination mount and the cloned mount is made slave
* of the same master as that of the source mount. The cloned mount
* is marked as 'shared and slave'.
* (*) the cloned mount is made a slave of the same master as that of the
* source mount.
*
* --------------------------------------------------------------
* | MOVE MOUNT OPERATION |
* |*************************************************************
* | source-->| shared | private | slave |
* | dest | | | |
* | | | | | |
* | v | | | |
* |*************************************************************
* | shared | shared (+) | shared (+) | shared(+++) |
* | | | | |
* |non-shared| shared (+*) | private | slave (*) |
* **************************************************************
*
* (+) the mount is moved to the destination. And is then propagated to
* all the mounts in the propagation tree of the destination mount.
* (+*) the mount is moved to the destination.
* (+++) the mount is moved to the destination and is then propagated to
* all the mounts belonging to the destination mount's propagation tree.
* the mount is marked as 'shared and slave'.
* (*) the mount continues to be a slave at the new location.
*
* if the source mount is a tree, the operations explained above is
* applied to each mount in the tree.
Expand Down
81 changes: 72 additions & 9 deletions fs/pnode.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,16 @@ static inline struct vfsmount *next_peer(struct vfsmount *p)
return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
}

static inline struct vfsmount *first_slave(struct vfsmount *p)
{
return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
}

static inline struct vfsmount *next_slave(struct vfsmount *p)
{
return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
}

static int do_make_slave(struct vfsmount *mnt)
{
struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
Expand Down Expand Up @@ -83,10 +93,64 @@ void change_mnt_propagation(struct vfsmount *mnt, int type)
static struct vfsmount *propagation_next(struct vfsmount *m,
struct vfsmount *origin)
{
m = next_peer(m);
if (m == origin)
return NULL;
return m;
/* are there any slaves of this mount? */
if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
return first_slave(m);

while (1) {
struct vfsmount *next;
struct vfsmount *master = m->mnt_master;

if ( master == origin->mnt_master ) {
next = next_peer(m);
return ((next == origin) ? NULL : next);
} else if (m->mnt_slave.next != &master->mnt_slave_list)
return next_slave(m);

/* back at master */
m = master;
}
}

/*
* return the source mount to be used for cloning
*
* @dest the current destination mount
* @last_dest the last seen destination mount
* @last_src the last seen source mount
* @type return CL_SLAVE if the new mount has to be
* cloned as a slave.
*/
static struct vfsmount *get_source(struct vfsmount *dest,
struct vfsmount *last_dest,
struct vfsmount *last_src,
int *type)
{
struct vfsmount *p_last_src = NULL;
struct vfsmount *p_last_dest = NULL;
*type = CL_PROPAGATION;;

if (IS_MNT_SHARED(dest))
*type |= CL_MAKE_SHARED;

while (last_dest != dest->mnt_master) {
p_last_dest = last_dest;
p_last_src = last_src;
last_dest = last_dest->mnt_master;
last_src = last_src->mnt_master;
}

if (p_last_dest) {
do {
p_last_dest = next_peer(p_last_dest);
} while (IS_MNT_NEW(p_last_dest));
}

if (dest != p_last_dest) {
*type |= CL_SLAVE;
return last_src;
} else
return p_last_src;
}

/*
Expand Down Expand Up @@ -114,16 +178,15 @@ int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,

for (m = propagation_next(dest_mnt, dest_mnt); m;
m = propagation_next(m, dest_mnt)) {
int type = CL_PROPAGATION;
int type;
struct vfsmount *source;

if (IS_MNT_NEW(m))
continue;

if (IS_MNT_SHARED(m))
type |= CL_MAKE_SHARED;
source = get_source(m, prev_dest_mnt, prev_src_mnt, &type);

if (!(child = copy_tree(source_mnt, source_mnt->mnt_root,
type))) {
if (!(child = copy_tree(source, source->mnt_root, type))) {
ret = -ENOMEM;
list_splice(tree_list, tmp_list.prev);
goto out;
Expand Down

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