[PATCH] introduce shared mounts

This creates shared mounts.  A shared mount when bind-mounted to some
mountpoint, propagates mount/umount events to each other.  All the
shared mounts that propagate events to each other belong to the same
peer-group.

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, 21 insertions, 2 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 3782923d6d4d..f6861a5487df 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -68,6 +68,7 @@ struct vfsmount *alloc_vfsmnt(const char *name)
                 INIT_LIST_HEAD(&mnt->mnt_mounts);
                 INIT_LIST_HEAD(&mnt->mnt_list);
                 INIT_LIST_HEAD(&mnt->mnt_expire);
+                INIT_LIST_HEAD(&mnt->mnt_share);
                 if (name) {
                         int size = strlen(name) + 1;
                         char *newname = kmalloc(size, GFP_KERNEL);
@@ -1113,7 +1114,7 @@ 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_PRIVATE)
+        else if (flags & (MS_SHARED | MS_PRIVATE))
                 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 aaa0dffda12a..1e22165ea41f 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -11,7 +11,18 @@
 #include <linux/fs.h>
 #include "pnode.h"
 
+/* return the next shared peer mount of @p */
+static inline struct vfsmount *next_peer(struct vfsmount *p)
+{
+        return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
+}
+
 void change_mnt_propagation(struct vfsmount *mnt, int type)
 {
-        mnt->mnt_flags &= ~MNT_PNODE_MASK;
+        if (type == MS_SHARED) {
+                mnt->mnt_flags |= MNT_SHARED;
+        } else {
+                list_del_init(&mnt->mnt_share);
+                mnt->mnt_flags &= ~MNT_PNODE_MASK;
+        }
 }
diff --git a/fs/pnode.h b/fs/pnode.h
index 33549a3a74eb..ab1bdaee4e08 100644
--- a/fs/pnode.h
+++ b/fs/pnode.h
@@ -10,5 +10,9 @@
 
 #include <linux/list.h>
 #include <linux/mount.h>
+
+#define IS_MNT_SHARED(mnt) (mnt->mnt_flags & MNT_SHARED)
+#define CLEAR_MNT_SHARED(mnt) (mnt->mnt_flags &= ~MNT_SHARED)
+
 void change_mnt_propagation(struct vfsmount *, int);
 #endif /* _LINUX_PNODE_H */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6c431086abb3..551fba303cf8 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_SHARED       (1<<20) /* change to shared */
 #define MS_POSIXACL     (1<<16) /* VFS does not apply the umask */
 #define MS_ACTIVE       (1<<30)
 #define MS_NOUSER       (1<<31)
diff --git a/include/linux/mount.h b/include/linux/mount.h
index 8eadd3b65899..2582559718fc 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -20,6 +20,7 @@
 #define MNT_NOSUID      0x01
 #define MNT_NODEV       0x02
 #define MNT_NOEXEC      0x04
+#define MNT_SHARED      0x10    /* if the vfsmount is a shared mount */
 #define MNT_PNODE_MASK  0x30    /* propogation flag mask */
 
 struct vfsmount {
@@ -36,6 +37,7 @@ struct vfsmount {
         char *mnt_devname;              /* Name of device e.g. /dev/dsk/hda1 */
         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 namespace *mnt_namespace; /* containing namespace */
         int mnt_pinned;
 };