Commit ea5b778a authored by David Howells's avatar David Howells Committed by Al Viro

Unexport do_add_mount() and add in follow_automount(), not ->d_automount()

Unexport do_add_mount() and make ->d_automount() return the vfsmount to be
added rather than calling do_add_mount() itself.  follow_automount() will then
do the addition.

This slightly complicates things as ->d_automount() normally wants to add the
new vfsmount to an expiration list and start an expiration timer.  The problem
with that is that the vfsmount will be deleted if it has a refcount of 1 and
the timer will not repeat if the expiration list is empty.

To this end, we require the vfsmount to be returned from d_automount() with a
refcount of (at least) 2.  One of these refs will be dropped unconditionally.
In addition, follow_automount() must get a 3rd ref around the call to
do_add_mount() lest it eat a ref and return an error, leaving the mount we
have open to being expired as we would otherwise have only 1 ref on it.

d_automount() should also add the the vfsmount to the expiration list (by
calling mnt_set_expiry()) and start the expiration timer before returning, if
this mechanism is to be used.  The vfsmount will be unlinked from the
expiration list by follow_automount() if do_add_mount() fails.

This patch also fixes the call to do_add_mount() for AFS to propagate the mount
flags from the parent vfsmount.
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent ab90911f
......@@ -933,15 +933,20 @@ struct dentry_operations {
dynamic_dname() helper function is provided to take care of this.
d_automount: called when an automount dentry is to be traversed (optional).
This should create a new VFS mount record, mount it on the directory
and return the record to the caller. The caller is supplied with a
path parameter giving the automount directory to describe the automount
target and the parent VFS mount record to provide inheritable mount
parameters. NULL should be returned if someone else managed to make
the automount first. If the automount failed, then an error code
should be returned. If -EISDIR is returned, then the directory will
be treated as an ordinary directory and returned to pathwalk to
continue walking.
This should create a new VFS mount record and return the record to the
caller. The caller is supplied with a path parameter giving the
automount directory to describe the automount target and the parent
VFS mount record to provide inheritable mount parameters. NULL should
be returned if someone else managed to make the automount first. If
the vfsmount creation failed, then an error code should be returned.
If -EISDIR is returned, then the directory will be treated as an
ordinary directory and returned to pathwalk to continue walking.
If a vfsmount is returned, the caller will attempt to mount it on the
mountpoint and will remove the vfsmount from its expiration list in
the case of failure. The vfsmount should be returned with 2 refs on
it to prevent automatic expiration - the caller will clean up the
additional ref.
This function is only used if DCACHE_NEED_AUTOMOUNT is set on the
dentry. This is set by __d_instantiate() if S_AUTOMOUNT is set on the
......
......@@ -241,7 +241,6 @@ static struct vfsmount *afs_mntpt_do_automount(struct dentry *mntpt)
struct vfsmount *afs_d_automount(struct path *path)
{
struct vfsmount *newmnt;
int err;
_enter("{%s,%s}", path->mnt->mnt_devname, path->dentry->d_name.name);
......@@ -249,24 +248,12 @@ struct vfsmount *afs_d_automount(struct path *path)
if (IS_ERR(newmnt))
return newmnt;
mntget(newmnt);
err = do_add_mount(newmnt, path, MNT_SHRINKABLE, &afs_vfsmounts);
switch (err) {
case 0:
queue_delayed_work(afs_wq, &afs_mntpt_expiry_timer,
afs_mntpt_expiry_timeout * HZ);
_leave(" = %p {%s}", newmnt, newmnt->mnt_devname);
return newmnt;
case -EBUSY:
/* someone else made a mount here whilst we were busy */
mntput(newmnt);
_leave(" = NULL [EBUSY]");
return NULL;
default:
mntput(newmnt);
_leave(" = %d", err);
return ERR_PTR(err);
}
mntget(newmnt); /* prevent immediate expiration */
mnt_set_expiry(newmnt, &afs_vfsmounts);
queue_delayed_work(afs_wq, &afs_mntpt_expiry_timer,
afs_mntpt_expiry_timeout * HZ);
_leave(" = %p {%s}", newmnt, newmnt->mnt_devname);
return newmnt;
}
/*
......
......@@ -351,7 +351,6 @@ static struct vfsmount *cifs_dfs_do_automount(struct dentry *mntpt)
struct vfsmount *cifs_dfs_d_automount(struct path *path)
{
struct vfsmount *newmnt;
int err;
cFYI(1, "in %s", __func__);
......@@ -361,25 +360,12 @@ struct vfsmount *cifs_dfs_d_automount(struct path *path)
return newmnt;
}
mntget(newmnt);
err = do_add_mount(newmnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE,
&cifs_dfs_automount_list);
switch (err) {
case 0:
schedule_delayed_work(&cifs_dfs_automount_task,
cifs_dfs_mountpoint_expiry_timeout);
cFYI(1, "leaving %s [ok]" , __func__);
return newmnt;
case -EBUSY:
/* someone else made a mount here whilst we were busy */
mntput(newmnt);
cFYI(1, "leaving %s [EBUSY]" , __func__);
return NULL;
default:
mntput(newmnt);
cFYI(1, "leaving %s [error %d]" , __func__, err);
return ERR_PTR(err);
}
mntget(newmnt); /* prevent immediate expiration */
mnt_set_expiry(newmnt, &cifs_dfs_automount_list);
schedule_delayed_work(&cifs_dfs_automount_task,
cifs_dfs_mountpoint_expiry_timeout);
cFYI(1, "leaving %s [ok]" , __func__);
return newmnt;
}
const struct inode_operations cifs_dfs_referral_inode_operations = {
......
......@@ -70,6 +70,8 @@ extern void mnt_set_mountpoint(struct vfsmount *, struct dentry *,
extern void release_mounts(struct list_head *);
extern void umount_tree(struct vfsmount *, int, struct list_head *);
extern struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int);
extern int do_add_mount(struct vfsmount *, struct path *, int);
extern void mnt_clear_expiry(struct vfsmount *);
extern void __init mnt_init(void);
......
......@@ -900,6 +900,7 @@ static int follow_automount(struct path *path, unsigned flags,
bool *need_mntput)
{
struct vfsmount *mnt;
int err;
if (!path->dentry->d_op || !path->dentry->d_op->d_automount)
return -EREMOTE;
......@@ -942,22 +943,49 @@ static int follow_automount(struct path *path, unsigned flags,
return -EREMOTE;
return PTR_ERR(mnt);
}
if (!mnt) /* mount collision */
return 0;
/* The new mount record should have at least 2 refs to prevent it being
* expired before we get a chance to add it
*/
BUG_ON(mnt_get_count(mnt) < 2);
if (mnt->mnt_sb == path->mnt->mnt_sb &&
mnt->mnt_root == path->dentry) {
mnt_clear_expiry(mnt);
mntput(mnt);
mntput(mnt);
return -ELOOP;
}
dput(path->dentry);
if (*need_mntput)
mntput(path->mnt);
path->mnt = mnt;
path->dentry = dget(mnt->mnt_root);
*need_mntput = true;
return 0;
/* We need to add the mountpoint to the parent. The filesystem may
* have placed it on an expiry list, and so we need to make sure it
* won't be expired under us if do_add_mount() fails (do_add_mount()
* will eat a reference unconditionally).
*/
mntget(mnt);
err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
switch (err) {
case -EBUSY:
/* Someone else made a mount here whilst we were busy */
err = 0;
default:
mnt_clear_expiry(mnt);
mntput(mnt);
mntput(mnt);
return err;
case 0:
mntput(mnt);
dput(path->dentry);
if (*need_mntput)
mntput(path->mnt);
path->mnt = mnt;
path->dentry = dget(mnt->mnt_root);
*need_mntput = true;
return 0;
}
}
/*
......
......@@ -1925,15 +1925,14 @@ static int do_new_mount(struct path *path, char *type, int flags,
if (IS_ERR(mnt))
return PTR_ERR(mnt);
return do_add_mount(mnt, path, mnt_flags, NULL);
return do_add_mount(mnt, path, mnt_flags);
}
/*
* add a mount into a namespace's mount tree
* - provide the option of adding the new mount to an expiration list
* - this unconditionally eats one of the caller's references to newmnt.
*/
int do_add_mount(struct vfsmount *newmnt, struct path *path,
int mnt_flags, struct list_head *fslist)
int do_add_mount(struct vfsmount *newmnt, struct path *path, int mnt_flags)
{
int err;
......@@ -1963,9 +1962,6 @@ int do_add_mount(struct vfsmount *newmnt, struct path *path,
if ((err = graft_tree(newmnt, path)))
goto unlock;
if (fslist) /* add to the specified expiration list */
list_add_tail(&newmnt->mnt_expire, fslist);
up_write(&namespace_sem);
return 0;
......@@ -1975,7 +1971,36 @@ int do_add_mount(struct vfsmount *newmnt, struct path *path,
return err;
}
EXPORT_SYMBOL_GPL(do_add_mount);
/**
* mnt_set_expiry - Put a mount on an expiration list
* @mnt: The mount to list.
* @expiry_list: The list to add the mount to.
*/
void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
{
down_write(&namespace_sem);
br_write_lock(vfsmount_lock);
list_add_tail(&mnt->mnt_expire, expiry_list);
br_write_unlock(vfsmount_lock);
up_write(&namespace_sem);
}
EXPORT_SYMBOL(mnt_set_expiry);
/*
* Remove a vfsmount from any expiration list it may be on
*/
void mnt_clear_expiry(struct vfsmount *mnt)
{
if (!list_empty(&mnt->mnt_expire)) {
down_write(&namespace_sem);
br_write_lock(vfsmount_lock);
list_del_init(&mnt->mnt_expire);
br_write_unlock(vfsmount_lock);
up_write(&namespace_sem);
}
}
/*
* process a list of expirable mountpoints with the intent of discarding any
......
......@@ -149,26 +149,10 @@ struct vfsmount *nfs_d_automount(struct path *path)
if (IS_ERR(mnt))
goto out;
mntget(mnt);
err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE,
&nfs_automount_list);
switch (err) {
case 0:
dprintk("%s: done, success\n", __func__);
schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
break;
case -EBUSY:
/* someone else made a mount here whilst we were busy */
mntput(mnt);
dprintk("%s: done, collision\n", __func__);
mnt = NULL;
break;
default:
mntput(mnt);
dprintk("%s: done, error %d\n", __func__, err);
mnt = ERR_PTR(err);
break;
}
dprintk("%s: done, success\n", __func__);
mntget(mnt); /* prevent immediate expiration */
mnt_set_expiry(mnt, &nfs_automount_list);
schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
out:
nfs_free_fattr(fattr);
......
......@@ -110,12 +110,7 @@ extern struct vfsmount *vfs_kern_mount(struct file_system_type *type,
int flags, const char *name,
void *data);
struct nameidata;
struct path;
extern int do_add_mount(struct vfsmount *newmnt, struct path *path,
int mnt_flags, struct list_head *fslist);
extern void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list);
extern void mark_mounts_for_expiry(struct list_head *mounts);
extern dev_t name_to_dev_t(char *name);
......
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