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Subject[patch 7/7] vfs: mountinfo: show dominating group id
From: Miklos Szeredi <mszeredi@suse.cz>

Show peer group ID of nearest dominating group that has intersection
with the mount's namespace.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
Documentation/filesystems/proc.txt | 6 ++++
fs/namespace.c | 9 +++++-
fs/pnode.c | 51 +++++++++++++++++++++++++++++++++++++
fs/pnode.h | 1
4 files changed, 65 insertions(+), 2 deletions(-)
Index: vfs-2.6/Documentation/filesystems/proc.txt
===================================================================
--- vfs-2.6.orig/Documentation/filesystems/proc.txt 2008-03-27 12:06:15.000000000 +0100
+++ vfs-2.6/Documentation/filesystems/proc.txt 2008-03-27 12:06:17.000000000 +0100
@@ -2374,8 +2374,14 @@ possible optional fields are:

shared:X mount is shared in peer group X
master:X mount is slave to peer group X
+propagate_from:X mount is slave and receives propagation from peer group X (*)
unbindable mount is unbindable

+(*) X is the closest dominant peer group under the process's root. If
+X is the immediate master of the mount, or if there's no dominant peer
+group under the same root, then only the "master:X" field is present
+and not the "propagate_from:X" field.
+
For more information on mount propagation see:

Documentation/filesystems/sharedsubtree.txt
Index: vfs-2.6/fs/namespace.c
===================================================================
--- vfs-2.6.orig/fs/namespace.c 2008-03-27 12:06:15.000000000 +0100
+++ vfs-2.6/fs/namespace.c 2008-03-27 12:06:17.000000000 +0100
@@ -836,8 +836,13 @@ static int show_mountinfo(struct seq_fil
/* Tagged fields ("foo:X" or "bar") */
if (IS_MNT_SHARED(mnt))
seq_printf(m, " shared:%i", mnt->mnt_group_id);
- if (IS_MNT_SLAVE(mnt))
- seq_printf(m, " master:%i", mnt->mnt_master->mnt_group_id);
+ if (IS_MNT_SLAVE(mnt)) {
+ int master = mnt->mnt_master->mnt_group_id;
+ int dom = get_dominating_id(mnt, &p->root);
+ seq_printf(m, " master:%i", master);
+ if (dom && dom != master)
+ seq_printf(m, " propagate_from:%i", dom);
+ }
if (IS_MNT_UNBINDABLE(mnt))
seq_puts(m, " unbindable");

Index: vfs-2.6/fs/pnode.c
===================================================================
--- vfs-2.6.orig/fs/pnode.c 2008-03-27 12:06:10.000000000 +0100
+++ vfs-2.6/fs/pnode.c 2008-03-27 12:06:17.000000000 +0100
@@ -28,6 +28,57 @@ static inline struct vfsmount *next_slav
return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
}

+/*
+ * Return true if path is reachable from root
+ *
+ * namespace_sem is held, and mnt is attached
+ */
+static bool is_path_reachable(struct vfsmount *mnt, struct dentry *dentry,
+ const struct path *root)
+{
+ while (mnt != root->mnt && mnt->mnt_parent != mnt) {
+ dentry = mnt->mnt_mountpoint;
+ mnt = mnt->mnt_parent;
+ }
+ return mnt == root->mnt && is_subdir(dentry, root->dentry);
+}
+
+static struct vfsmount *get_peer_under_root(struct vfsmount *mnt,
+ struct mnt_namespace *ns,
+ const struct path *root)
+{
+ struct vfsmount *m = mnt;
+
+ do {
+ /* Check the namespace first for optimization */
+ if (m->mnt_ns == ns && is_path_reachable(m, m->mnt_root, root))
+ return m;
+
+ m = next_peer(m);
+ } while (m != mnt);
+
+ return NULL;
+}
+
+/*
+ * Get ID of closest dominating peer group having a representative
+ * under the given root.
+ *
+ * Caller must hold namespace_sem
+ */
+int get_dominating_id(struct vfsmount *mnt, const struct path *root)
+{
+ struct vfsmount *m;
+
+ for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
+ struct vfsmount *d = get_peer_under_root(m, mnt->mnt_ns, root);
+ if (d)
+ return d->mnt_group_id;
+ }
+
+ return 0;
+}
+
static int do_make_slave(struct vfsmount *mnt)
{
struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
Index: vfs-2.6/fs/pnode.h
===================================================================
--- vfs-2.6.orig/fs/pnode.h 2008-03-27 12:06:10.000000000 +0100
+++ vfs-2.6/fs/pnode.h 2008-03-27 12:06:17.000000000 +0100
@@ -36,4 +36,5 @@ int propagate_mnt(struct vfsmount *, str
int propagate_umount(struct list_head *);
int propagate_mount_busy(struct vfsmount *, int);
void mnt_release_group_id(struct vfsmount *);
+int get_dominating_id(struct vfsmount *mnt, const struct path *root);
#endif /* _LINUX_PNODE_H */
--


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