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Subject[PATCH 09/25] vfs: Add mount notification count [ver #14]
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Add a notification count on mount objects so that the user can easily check
to see if a mount has changed its attributes or its children.

Future patches will:

(1) Provide this value through fsinfo() attributes.

(2) Hook into the notify_mount() function to provide a notification
interface for userspace to monitor.

Signed-off-by: David Howells <dhowells@redhat.com>
---

fs/mount.h | 22 ++++++++++++++++++++++
fs/namespace.c | 13 +++++++++++++
2 files changed, 35 insertions(+)

diff --git a/fs/mount.h b/fs/mount.h
index 6250de544760..47795802f78e 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -70,6 +70,7 @@ struct mount {
struct hlist_head mnt_pins;
struct fs_pin mnt_umount;
struct dentry *mnt_ex_mountpoint;
+ atomic_t mnt_notify_counter; /* Number of notifications generated */
} __randomize_layout;

#define MNT_NS_INTERNAL ERR_PTR(-EINVAL) /* distinct from any mnt_namespace */
@@ -151,3 +152,24 @@ static inline bool is_anon_ns(struct mnt_namespace *ns)
{
return ns->seq == 0;
}
+
+/*
+ * Type of mount topology change notification.
+ */
+enum mount_notification_subtype {
+ NOTIFY_MOUNT_NEW_MOUNT = 0, /* New mount added */
+ NOTIFY_MOUNT_UNMOUNT = 1, /* Mount removed manually */
+ NOTIFY_MOUNT_EXPIRY = 2, /* Automount expired */
+ NOTIFY_MOUNT_READONLY = 3, /* Mount R/O state changed */
+ NOTIFY_MOUNT_SETATTR = 4, /* Mount attributes changed */
+ NOTIFY_MOUNT_MOVE_FROM = 5, /* Mount moved from here */
+ NOTIFY_MOUNT_MOVE_TO = 6, /* Mount moved to here (compare op_id) */
+};
+
+static inline void notify_mount(struct mount *changed,
+ struct mount *aux,
+ enum mount_notification_subtype subtype,
+ u32 info_flags)
+{
+ atomic_inc(&changed->mnt_notify_counter);
+}
diff --git a/fs/namespace.c b/fs/namespace.c
index a49a7d9ed482..1450faab96b9 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -513,6 +513,8 @@ static int mnt_make_readonly(struct mount *mnt)
smp_wmb();
mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
unlock_mount_hash();
+ if (ret == 0)
+ notify_mount(mnt, NULL, NOTIFY_MOUNT_READONLY, 0x10000);
return ret;
}

@@ -521,6 +523,7 @@ static int __mnt_unmake_readonly(struct mount *mnt)
lock_mount_hash();
mnt->mnt.mnt_flags &= ~MNT_READONLY;
unlock_mount_hash();
+ notify_mount(mnt, NULL, NOTIFY_MOUNT_READONLY, 0);
return 0;
}

@@ -833,6 +836,7 @@ static void umount_mnt(struct mount *mnt)
{
/* old mountpoint will be dropped when we can do that */
mnt->mnt_ex_mountpoint = mnt->mnt_mountpoint;
+ notify_mount(mnt->mnt_parent, mnt, NOTIFY_MOUNT_UNMOUNT, 0);
unhash_mnt(mnt);
}

@@ -1472,6 +1476,7 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
p = list_first_entry(&tmp_list, struct mount, mnt_list);
list_del_init(&p->mnt_expire);
list_del_init(&p->mnt_list);
+
ns = p->mnt_ns;
if (ns) {
ns->mounts--;
@@ -2095,7 +2100,10 @@ static int attach_recursive_mnt(struct mount *source_mnt,
lock_mount_hash();
}
if (parent_path) {
+ notify_mount(source_mnt->mnt_parent, source_mnt,
+ NOTIFY_MOUNT_MOVE_FROM, 0);
detach_mnt(source_mnt, parent_path);
+ notify_mount(dest_mnt, source_mnt, NOTIFY_MOUNT_MOVE_TO, 0);
attach_mnt(source_mnt, dest_mnt, dest_mp);
touch_mnt_namespace(source_mnt->mnt_ns);
} else {
@@ -2104,6 +2112,9 @@ static int attach_recursive_mnt(struct mount *source_mnt,
list_del_init(&source_mnt->mnt_ns->list);
}
mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
+ notify_mount(dest_mnt, source_mnt, NOTIFY_MOUNT_NEW_MOUNT,
+ source_mnt->mnt.mnt_sb->s_flags & SB_SUBMOUNT ?
+ 0x10000 : 0);
commit_tree(source_mnt);
}

@@ -2480,6 +2491,7 @@ static void set_mount_attributes(struct mount *mnt, unsigned int mnt_flags)
mnt->mnt.mnt_flags = mnt_flags;
touch_mnt_namespace(mnt->mnt_ns);
unlock_mount_hash();
+ notify_mount(mnt, NULL, NOTIFY_MOUNT_SETATTR, 0);
}

/*
@@ -2880,6 +2892,7 @@ void mark_mounts_for_expiry(struct list_head *mounts)
if (!xchg(&mnt->mnt_expiry_mark, 1) ||
propagate_mount_busy(mnt, 1))
continue;
+ notify_mount(mnt, NULL, NOTIFY_MOUNT_EXPIRY, 0);
list_move(&mnt->mnt_expire, &graveyard);
}
while (!list_empty(&graveyard)) {
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