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Subject[PATCH 23/41] union-mount: Changes to the namespace handling
Date
From: Jan Blunck <jblunck@suse.de>

Creates the proper struct union_mount when mounting something into a
union. If the topmost filesystem isn't capable of handling the white-out
filetype it could only be mount read-only.

Signed-off-by: Jan Blunck <jblunck@suse.de>
Signed-off-by: Valerie Aurora <vaurora@redhat.com>
---
fs/namespace.c | 7 ++++++
fs/union.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/mount.h | 3 ++
include/linux/union.h | 10 +++++++-
4 files changed, 75 insertions(+), 2 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index dc01385..0280e5b 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -158,6 +158,9 @@ struct vfsmount *alloc_vfsmnt(const char *name)
#else
mnt->mnt_writers = 0;
#endif
+#ifdef CONFIG_UNION_MOUNT
+ INIT_LIST_HEAD(&mnt->mnt_unions);
+#endif
}
return mnt;

@@ -470,6 +473,7 @@ static void __touch_mnt_namespace(struct mnt_namespace *ns)

static void detach_mnt(struct vfsmount *mnt, struct path *old_path)
{
+ detach_mnt_union(mnt);
old_path->dentry = mnt->mnt_mountpoint;
old_path->mnt = mnt->mnt_parent;
mnt->mnt_parent = mnt;
@@ -493,6 +497,7 @@ static void attach_mnt(struct vfsmount *mnt, struct path *path)
list_add_tail(&mnt->mnt_hash, mount_hashtable +
hash(path->mnt, path->dentry));
list_add_tail(&mnt->mnt_child, &path->mnt->mnt_mounts);
+ attach_mnt_union(mnt, path->mnt, path->dentry);
}

/*
@@ -515,6 +520,7 @@ static void commit_tree(struct vfsmount *mnt)
list_add_tail(&mnt->mnt_hash, mount_hashtable +
hash(parent, mnt->mnt_mountpoint));
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
+ attach_mnt_union(mnt, mnt->mnt_parent, mnt->mnt_mountpoint);
touch_mnt_namespace(n);
}

@@ -986,6 +992,7 @@ void release_mounts(struct list_head *head)
struct dentry *dentry;
struct vfsmount *m;
spin_lock(&vfsmount_lock);
+ detach_mnt_union(mnt);
dentry = mnt->mnt_mountpoint;
m = mnt->mnt_parent;
mnt->mnt_mountpoint = mnt->mnt_root;
diff --git a/fs/union.c b/fs/union.c
index 6b99393..341fc03 100644
--- a/fs/union.c
+++ b/fs/union.c
@@ -113,6 +113,7 @@ struct union_mount *union_alloc(struct dentry *this, struct vfsmount *this_mnt,

atomic_set(&um->u_count, 1);
INIT_LIST_HEAD(&um->u_unions);
+ INIT_LIST_HEAD(&um->u_list);
INIT_HLIST_NODE(&um->u_hash);
INIT_HLIST_NODE(&um->u_rhash);

@@ -256,6 +257,7 @@ int append_to_union(struct vfsmount *mnt, struct dentry *dentry,
union_put(this);
return 0;
}
+ list_add(&this->u_list, &mnt->mnt_unions);
list_add(&this->u_unions, &dentry->d_unions);
dest_dentry->d_unionized++;
__union_hash(this);
@@ -365,6 +367,7 @@ repeat:
list_for_each_entry_safe(this, next, &dentry->d_unions, u_unions) {
BUG_ON(!hlist_unhashed(&this->u_hash));
BUG_ON(!hlist_unhashed(&this->u_rhash));
+ list_del(&this->u_list);
list_del(&this->u_unions);
this->u_next.dentry->d_unionized--;
spin_unlock(&union_lock);
@@ -393,6 +396,7 @@ repeat:

BUG_ON(!hlist_unhashed(&this->u_hash));
BUG_ON(!hlist_unhashed(&this->u_rhash));
+ list_del(&this->u_list);
list_del(&this->u_unions);
this->u_next.dentry->d_unionized--;
spin_unlock(&union_lock);
@@ -404,3 +408,56 @@ repeat:
}
spin_unlock(&union_lock);
}
+
+/*
+ * Remove all union_mounts structures belonging to this vfsmount from the
+ * union lookup hashtable and so on ...
+ */
+void shrink_mnt_unions(struct vfsmount *mnt)
+{
+ struct union_mount *this, *next;
+
+repeat:
+ spin_lock(&union_lock);
+ list_for_each_entry_safe(this, next, &mnt->mnt_unions, u_list) {
+ if (this->u_this.dentry == mnt->mnt_root)
+ continue;
+ __union_unhash(this);
+ list_del(&this->u_list);
+ list_del(&this->u_unions);
+ this->u_next.dentry->d_unionized--;
+ spin_unlock(&union_lock);
+ union_put(this);
+ goto repeat;
+ }
+ spin_unlock(&union_lock);
+}
+
+int attach_mnt_union(struct vfsmount *mnt, struct vfsmount *dest_mnt,
+ struct dentry *dest_dentry)
+{
+ if (!IS_MNT_UNION(mnt))
+ return 0;
+
+ return append_to_union(mnt, mnt->mnt_root, dest_mnt, dest_dentry);
+}
+
+void detach_mnt_union(struct vfsmount *mnt)
+{
+ struct union_mount *um;
+
+ if (!IS_MNT_UNION(mnt))
+ return;
+
+ shrink_mnt_unions(mnt);
+
+ spin_lock(&union_lock);
+ um = union_lookup(mnt->mnt_root, mnt);
+ __union_unhash(um);
+ list_del(&um->u_list);
+ list_del(&um->u_unions);
+ um->u_next.dentry->d_unionized--;
+ spin_unlock(&union_lock);
+ union_put(um);
+ return;
+}
diff --git a/include/linux/mount.h b/include/linux/mount.h
index e175c47..70c4f1f 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -54,6 +54,9 @@ struct vfsmount {
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 */
+#ifdef CONFIG_UNION_MOUNT
+ struct list_head mnt_unions; /* list of union_mount structures */
+#endif
struct mnt_namespace *mnt_ns; /* containing namespace */
int mnt_id; /* mount identifier */
int mnt_group_id; /* peer group identifier */
diff --git a/include/linux/union.h b/include/linux/union.h
index b035a82..0b6f356 100644
--- a/include/linux/union.h
+++ b/include/linux/union.h
@@ -30,8 +30,9 @@ struct union_mount {
atomic_t u_count; /* reference count */
struct mutex u_mutex;
struct list_head u_unions; /* list head for d_unions */
- struct hlist_node u_hash; /* list head for searching */
- struct hlist_node u_rhash; /* list head for reverse searching */
+ struct list_head u_list; /* list head for mnt_unions */
+ struct hlist_node u_hash; /* list head for seaching */
+ struct hlist_node u_rhash; /* list head for reverse seaching */

struct path u_this; /* this is me */
struct path u_next; /* this is what I overlay */
@@ -49,6 +50,9 @@ extern int follow_union_mount(struct vfsmount **, struct dentry **);
extern void __d_drop_unions(struct dentry *);
extern void shrink_d_unions(struct dentry *);
extern void __shrink_d_unions(struct dentry *, struct list_head *);
+extern int attach_mnt_union(struct vfsmount *, struct vfsmount *,
+ struct dentry *);
+extern void detach_mnt_union(struct vfsmount *);

#else /* CONFIG_UNION_MOUNT */

@@ -61,6 +65,8 @@ extern void __shrink_d_unions(struct dentry *, struct list_head *);
#define __d_drop_unions(x) do { } while (0)
#define shrink_d_unions(x) do { } while (0)
#define __shrink_d_unions(x,y) do { } while (0)
+#define attach_mnt_union(x, y, z) do { } while (0)
+#define detach_mnt_union(x) do { } while (0)

#endif /* CONFIG_UNION_MOUNT */
#endif /* __KERNEL__ */
--
1.6.3.3


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