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Subject[PATCH 1/3] vfs: track count of child mounts
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While the total reference count of a mount is mostly all that's needed
the reference count corresponding to the mounts only is occassionally
also needed (for example, autofs checking if a tree of mounts can be
expired).

To make this reference count avaialble with minimal changes add a
counter to track the number of child mounts under a given mount. This
count can then be used to calculate the mounts only reference count.

Signed-off-by: Ian Kent <raven@themaw.net>
---
fs/mount.h | 1 +
fs/namespace.c | 8 ++++++++
2 files changed, 9 insertions(+)

diff --git a/fs/mount.h b/fs/mount.h
index 0b6e08cf8afb..3f0f62912463 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -52,6 +52,7 @@ struct mount {
int mnt_writers;
#endif
struct list_head mnt_mounts; /* list of children, anchored here */
+ unsigned int mnt_mounts_cnt; /* count of children, anchored here */
struct list_head mnt_child; /* and going through their mnt_child */
struct list_head mnt_instance; /* mount instance on sb->s_mounts */
const char *mnt_devname; /* Name of device e.g. /dev/dsk/hda1 */
diff --git a/fs/namespace.c b/fs/namespace.c
index e6a7e769d25d..3c1ee5b5bb69 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -882,6 +882,8 @@ static struct mountpoint *unhash_mnt(struct mount *mnt)
struct mountpoint *mp;
mnt->mnt_parent = mnt;
mnt->mnt_mountpoint = mnt->mnt.mnt_root;
+ if (!list_empty(&mnt->mnt_child))
+ mnt->mnt_parent->mnt_mounts_cnt--;
list_del_init(&mnt->mnt_child);
hlist_del_init_rcu(&mnt->mnt_hash);
hlist_del_init(&mnt->mnt_mp_list);
@@ -918,6 +920,7 @@ static void __attach_mnt(struct mount *mnt, struct mount *parent)
hlist_add_head_rcu(&mnt->mnt_hash,
m_hash(&parent->mnt, mnt->mnt_mountpoint));
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
+ parent->mnt_mounts_cnt++;
}

/*
@@ -936,6 +939,8 @@ void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct m
struct mountpoint *old_mp = mnt->mnt_mp;
struct mount *old_parent = mnt->mnt_parent;

+ if (!list_empty(&mnt->mnt_child))
+ mnt->mnt_parent->mnt_mounts_cnt--;
list_del_init(&mnt->mnt_child);
hlist_del_init(&mnt->mnt_mp_list);
hlist_del_init_rcu(&mnt->mnt_hash);
@@ -1562,6 +1567,8 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)

/* Hide the mounts from mnt_mounts */
list_for_each_entry(p, &tmp_list, mnt_list) {
+ if (!list_empty(&p->mnt_child))
+ p->mnt_parent->mnt_mounts_cnt--;
list_del_init(&p->mnt_child);
}

@@ -1590,6 +1597,7 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
if (!disconnect) {
/* Don't forget about p */
list_add_tail(&p->mnt_child, &p->mnt_parent->mnt_mounts);
+ p->mnt_parent->mnt_mounts_cnt++;
} else {
umount_mnt(p);
}

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