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Subject[patch 3/6] vfs: mountinfo stable peer group id
From: Miklos Szeredi <mszeredi@suse.cz>

Add a stable identifier for shared mounts.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
Documentation/filesystems/proc.txt | 12 +------
fs/namespace.c | 7 ++--
fs/pnode.c | 63 ++++++++++++++++++++++++-------------
fs/pnode.h | 1
include/linux/mount.h | 1
5 files changed, 52 insertions(+), 32 deletions(-)

Index: linux/fs/pnode.c
===================================================================
--- linux.orig/fs/pnode.c 2008-03-13 20:45:49.000000000 +0100
+++ linux/fs/pnode.c 2008-03-13 20:45:50.000000000 +0100
@@ -9,8 +9,12 @@
#include <linux/mnt_namespace.h>
#include <linux/mount.h>
#include <linux/fs.h>
+#include <linux/idr.h>
#include "pnode.h"

+static DEFINE_SPINLOCK(mnt_pgid_lock);
+static DEFINE_IDA(mnt_pgid_ida);
+
/* return the next shared peer mount of @p */
static inline struct vfsmount *next_peer(struct vfsmount *p)
{
@@ -27,47 +31,58 @@ static inline struct vfsmount *next_slav
return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
}

-void set_mnt_shared(struct vfsmount *mnt)
+static void __set_mnt_shared(struct vfsmount *mnt)
{
mnt->mnt_flags &= ~MNT_PNODE_MASK;
mnt->mnt_flags |= MNT_SHARED;
}

-void clear_mnt_shared(struct vfsmount *mnt)
+void set_mnt_shared(struct vfsmount *mnt)
{
- mnt->mnt_flags &= ~MNT_SHARED;
+ int res;
+
+ retry:
+ spin_lock(&mnt_pgid_lock);
+ if (IS_MNT_SHARED(mnt)) {
+ spin_unlock(&mnt_pgid_lock);
+ return;
+ }
+
+ res = ida_get_new(&mnt_pgid_ida, &mnt->mnt_pgid);
+ spin_unlock(&mnt_pgid_lock);
+ if (res == -EAGAIN) {
+ if (ida_pre_get(&mnt_pgid_ida, GFP_KERNEL))
+ goto retry;
+ }
+ __set_mnt_shared(mnt);
}

-static int __peer_group_id(struct vfsmount *mnt)
+void clear_mnt_shared(struct vfsmount *mnt)
{
- struct vfsmount *m;
- int id = mnt->mnt_id;
-
- for (m = next_peer(mnt); m != mnt; m = next_peer(m))
- id = min(id, m->mnt_id);
+ if (IS_MNT_SHARED(mnt)) {
+ mnt->mnt_flags &= ~MNT_SHARED;
+ mnt->mnt_pgid = -1;
+ }
+}

- return id;
+void make_mnt_peer(struct vfsmount *old, struct vfsmount *mnt)
+{
+ mnt->mnt_pgid = old->mnt_pgid;
+ list_add(&mnt->mnt_share, &old->mnt_share);
+ __set_mnt_shared(mnt);
}

-/* return the smallest ID within the peer group */
int get_peer_group_id(struct vfsmount *mnt)
{
- int id;
-
- spin_lock(&vfsmount_lock);
- id = __peer_group_id(mnt);
- spin_unlock(&vfsmount_lock);
-
- return id;
+ return mnt->mnt_pgid;
}

-/* return the smallest ID within the master's peer group */
int get_master_id(struct vfsmount *mnt)
{
int id;

spin_lock(&vfsmount_lock);
- id = __peer_group_id(mnt->mnt_master);
+ id = get_peer_group_id(mnt->mnt_master);
spin_unlock(&vfsmount_lock);

return id;
@@ -91,7 +106,13 @@ static int do_make_slave(struct vfsmount
if (peer_mnt == mnt)
peer_mnt = NULL;
}
- list_del_init(&mnt->mnt_share);
+ if (!list_empty(&mnt->mnt_share))
+ list_del_init(&mnt->mnt_share);
+ else if (IS_MNT_SHARED(mnt)) {
+ spin_lock(&mnt_pgid_lock);
+ ida_remove(&mnt_pgid_ida, mnt->mnt_pgid);
+ spin_unlock(&mnt_pgid_lock);
+ }

if (peer_mnt)
master = peer_mnt;
Index: linux/include/linux/mount.h
===================================================================
--- linux.orig/include/linux/mount.h 2008-03-13 20:45:15.000000000 +0100
+++ linux/include/linux/mount.h 2008-03-13 20:45:50.000000000 +0100
@@ -57,6 +57,7 @@ struct vfsmount {
struct vfsmount *mnt_master; /* slave is on master->mnt_slave_list */
struct mnt_namespace *mnt_ns; /* containing namespace */
int mnt_id; /* mount identifier */
+ int mnt_pgid; /* peer group identifier */
/*
* We put mnt_count & mnt_expiry_mark at the end of struct vfsmount
* to let these frequently modified fields in a separate cache line
Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c 2008-03-13 20:45:49.000000000 +0100
+++ linux/fs/namespace.c 2008-03-13 20:45:50.000000000 +0100
@@ -95,6 +95,7 @@ struct vfsmount *alloc_vfsmnt(const char
return NULL;
}

+ mnt->mnt_pgid = -1;
atomic_set(&mnt->mnt_count, 1);
INIT_LIST_HEAD(&mnt->mnt_hash);
INIT_LIST_HEAD(&mnt->mnt_child);
@@ -539,8 +540,10 @@ static struct vfsmount *clone_mnt(struct
mnt->mnt_master = old;
clear_mnt_shared(mnt);
} else if (!(flag & CL_PRIVATE)) {
- if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
- list_add(&mnt->mnt_share, &old->mnt_share);
+ if (flag & CL_PROPAGATION)
+ set_mnt_shared(old);
+ if (IS_MNT_SHARED(old))
+ make_mnt_peer(old, mnt);
if (IS_MNT_SLAVE(old))
list_add(&mnt->mnt_slave, &old->mnt_slave);
mnt->mnt_master = old->mnt_master;
Index: linux/Documentation/filesystems/proc.txt
===================================================================
--- linux.orig/Documentation/filesystems/proc.txt 2008-03-13 20:45:15.000000000 +0100
+++ linux/Documentation/filesystems/proc.txt 2008-03-13 20:45:50.000000000 +0100
@@ -2367,18 +2367,12 @@ MNTOPTS: per mount options
SBOPTS: per super block options
PROPAGATION: propagation type

-propagation type: <propagation_flag>[:<mntid>][,...]
- note: 'shared' flag is followed by the mntid of its peer mount
- 'slave' flag is followed by the mntid of its master mount
+propagation type: <propagation_flag>[:<peergrpid>][,...]
+ note: 'shared' flag is followed by the id of this mount's peer group
+ 'slave' flag is followed by the peer group id of its master mount
'private' flag stands by itself
'unbindable' flag stands by itself

-The 'mntid' used in the propagation type is a canonical ID of the peer
-group (currently the smallest ID within the group is used for this
-purpose, but this should not be relied on). Since mounts can be added
-or removed from the peer group, this ID only guaranteed to stay the
-same on a static propagation tree.
-
For more information see:

Documentation/filesystems/sharedsubtree.txt
Index: linux/fs/pnode.h
===================================================================
--- linux.orig/fs/pnode.h 2008-03-13 20:45:49.000000000 +0100
+++ linux/fs/pnode.h 2008-03-13 20:45:50.000000000 +0100
@@ -25,6 +25,7 @@

void set_mnt_shared(struct vfsmount *);
void clear_mnt_shared(struct vfsmount *);
+void make_mnt_peer(struct vfsmount *, struct vfsmount *);
void change_mnt_propagation(struct vfsmount *, int);
int propagate_mnt(struct vfsmount *, struct dentry *, struct vfsmount *,
struct list_head *);
--


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