[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>

diff --git a/fs/namespace.c b/fs/namespace.c
index 4b1af01..46f99bc 100644 (file)
--- 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 7bc942d..f73eba2 100644 (file)
--- 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 9b88ba0..b59f0e9 100644 (file)
--- 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 8bdb504..eef66f5 100644 (file)
--- 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 2582559..7e133ae 100644 (file)
--- 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;
 };