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

Documentation/filesystems/vfs.txt

+14 −9
Original line number Diff line number Diff line
@@ -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

fs/afs/mntpt.c

+6 −19
Original line number Diff line number Diff line
@@ -241,7 +241,6 @@ error_no_devname: 
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:

	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;

	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);

	}

}



/*

fs/cifs/cifs_dfs_ref.c

+6 −20
Original line number Diff line number Diff line
@@ -351,7 +351,6 @@ free_xid: 
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:

	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;

	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);

	}

}



const struct inode_operations cifs_dfs_referral_inode_operations = {

fs/internal.h

+2 −0
Original line number Diff line number Diff line
@@ -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);

fs/namei.c

+35 −7
Original line number Diff line number Diff line
@@ -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;
@@ -942,15 +943,41 @@ 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;

	}



	/* 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);
@@ -959,6 +986,7 @@ static int follow_automount(struct path *path, unsigned flags, 
		*need_mntput = true;

		return 0;

	}

}



/*

 * Handle a dentry that is managed in some way.

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