[PATCH] introduce slave mounts

A slave mount always has a master mount from which it receives
mount/umount events.  Unlike shared mount the event propagation does not
flow from the slave mount to the master.

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>

5 files changed, 60 insertions, 4 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 4b1af01c2fb4..46f99bc585bd 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -67,6 +67,8 @@ struct vfsmount *alloc_vfsmnt(const char *name)
                 INIT_LIST_HEAD(&mnt->mnt_list);
                 INIT_LIST_HEAD(&mnt->mnt_expire);
                 INIT_LIST_HEAD(&mnt->mnt_share);
+                INIT_LIST_HEAD(&mnt->mnt_slave_list);
+                INIT_LIST_HEAD(&mnt->mnt_slave);
                 if (name) {
                         int size = strlen(name) + 1;
                         char *newname = kmalloc(size, GFP_KERNEL);
@@ -1243,7 +1245,7 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
                                     data_page);
         else if (flags & MS_BIND)
                 retval = do_loopback(&nd, dev_name, flags & MS_REC);
-        else if (flags & (MS_SHARED | MS_PRIVATE))
+        else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE))
                 retval = do_change_type(&nd, flags);
         else if (flags & MS_MOVE)
                 retval = do_move_mount(&nd, dev_name);
diff --git a/fs/pnode.c b/fs/pnode.c
index 7bc942d047cd..f73eba24f1d1 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -17,13 +17,61 @@ static inline struct vfsmount *next_peer(struct vfsmount *p)
         return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
 }
 
+static int do_make_slave(struct vfsmount *mnt)
+{
+        struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
+        struct vfsmount *slave_mnt;
+
+        /*
+         * slave 'mnt' to a peer mount that has the
+         * same root dentry. If none is available than
+         * slave it to anything that is available.
+         */
+        while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
+               peer_mnt->mnt_root != mnt->mnt_root) ;
+
+        if (peer_mnt == mnt) {
+                peer_mnt = next_peer(mnt);
+                if (peer_mnt == mnt)
+                        peer_mnt = NULL;
+        }
+        list_del_init(&mnt->mnt_share);
+
+        if (peer_mnt)
+                master = peer_mnt;
+
+        if (master) {
+                list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
+                        slave_mnt->mnt_master = master;
+                list_del(&mnt->mnt_slave);
+                list_add(&mnt->mnt_slave, &master->mnt_slave_list);
+                list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
+                INIT_LIST_HEAD(&mnt->mnt_slave_list);
+        } else {
+                struct list_head *p = &mnt->mnt_slave_list;
+                while (!list_empty(p)) {
+                        slave_mnt = list_entry(p->next,
+                                        struct vfsmount, mnt_slave);
+                        list_del_init(&slave_mnt->mnt_slave);
+                        slave_mnt->mnt_master = NULL;
+                }
+        }
+        mnt->mnt_master = master;
+        CLEAR_MNT_SHARED(mnt);
+        INIT_LIST_HEAD(&mnt->mnt_slave_list);
+        return 0;
+}
+
 void change_mnt_propagation(struct vfsmount *mnt, int type)
 {
         if (type == MS_SHARED) {
                 set_mnt_shared(mnt);
-        } else {
-                list_del_init(&mnt->mnt_share);
-                mnt->mnt_flags &= ~MNT_PNODE_MASK;
+                return;
+        }
+        do_make_slave(mnt);
+        if (type != MS_SLAVE) {
+                list_del_init(&mnt->mnt_slave);
+                mnt->mnt_master = NULL;
         }
 }
 
diff --git a/fs/pnode.h b/fs/pnode.h
index 9b88ba06794a..b59f0e9fe6b1 100644
--- a/fs/pnode.h
+++ b/fs/pnode.h
@@ -12,10 +12,12 @@
 #include <linux/mount.h>
 
 #define IS_MNT_SHARED(mnt) (mnt->mnt_flags & MNT_SHARED)
+#define IS_MNT_SLAVE(mnt) (mnt->mnt_master)
 #define IS_MNT_NEW(mnt)  (!mnt->mnt_namespace)
 #define CLEAR_MNT_SHARED(mnt) (mnt->mnt_flags &= ~MNT_SHARED)
 
 #define CL_EXPIRE               0x01
+#define CL_SLAVE                0x02
 #define CL_COPY_ALL             0x04
 #define CL_MAKE_SHARED          0x08
 #define CL_PROPAGATION          0x10
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8bdb504be73b..eef66f54c017 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -105,6 +105,7 @@ extern int dir_notify_enable;
 #define MS_REC          16384
 #define MS_VERBOSE      32768
 #define MS_PRIVATE      (1<<18) /* change to private */
+#define MS_SLAVE        (1<<19) /* change to slave */
 #define MS_SHARED       (1<<20) /* change to shared */
 #define MS_POSIXACL     (1<<16) /* VFS does not apply the umask */
 #define MS_ACTIVE       (1<<30)
diff --git a/include/linux/mount.h b/include/linux/mount.h
index 2582559718fc..7e133ae2a94f 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -38,6 +38,9 @@ struct vfsmount {
         struct list_head mnt_list;
         struct list_head mnt_expire;    /* link in fs-specific expiry list */
         struct list_head mnt_share;     /* circular list of shared mounts */
+        struct list_head mnt_slave_list;/* list of slave mounts */
+        struct list_head mnt_slave;     /* slave list entry */
+        struct vfsmount *mnt_master;    /* slave is on master->mnt_slave_list */
         struct namespace *mnt_namespace; /* containing namespace */
         int mnt_pinned;
 };