Re: [RFC][PATCH 8/14] Union-mount lookup

From: Trond Myklebust
Date: Tue May 15 2007 - 10:01:06 EST

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On Mon, 2007-05-14 at 15:12 +0530, Bharata B Rao wrote:
> From: Jan Blunck <j.blunck@xxxxxxxxxxxxx>
> Subject: Union-mount lookup
>
> Modifies the vfs lookup routines to work with union mounted directories.
>
> The existing lookup routines generally lookup for a pathname only in the
> topmost or given directory. The changed versions of the lookup routines
> search for the pathname in the entire union mounted stack. Also they have been
> modified to setup the union stack during lookup from dcache cache and from
> real_lookup().
>
> Signed-off-by: Jan Blunck <j.blunck@xxxxxxxxxxxxx>
> Signed-off-by: Bharata B Rao <bharata@xxxxxxxxxxxxxxxxxx>
> ---
> fs/dcache.c | 16 +
> fs/namei.c | 78 +++++-
> fs/namespace.c | 35 ++
> fs/union.c | 598 +++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/dcache.h | 17 +
> include/linux/namei.h | 4
> include/linux/union.h | 49 ++++
> 7 files changed, 786 insertions(+), 11 deletions(-)
>
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -1286,7 +1286,7 @@ struct dentry * d_lookup(struct dentry *
> return dentry;
> }
>
> -struct dentry * __d_lookup(struct dentry * parent, struct qstr * name)
> +struct dentry * __d_lookup_single(struct dentry *parent, struct qstr *name)
> {
> unsigned int len = name->len;
> unsigned int hash = name->hash;
> @@ -1371,6 +1371,20 @@ out:
> return dentry;
> }
>
> +struct dentry * d_lookup_single(struct dentry *parent, struct qstr *name)
> +{
> + struct dentry *dentry;
> + unsigned long seq;
> +
> + do {
> + seq = read_seqbegin(&rename_lock);
> + dentry = __d_lookup_single(parent, name);
> + if (dentry)
> + break;
> + } while (read_seqretry(&rename_lock, seq));
> + return dentry;
> +}
> +
> /**
> * d_validate - verify dentry provided from insecure source
> * @dentry: The dentry alleged to be valid child of @dparent
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -374,6 +374,33 @@ void release_open_intent(struct nameidat
> }
>
> static inline struct dentry *
> +do_revalidate_single(struct dentry *dentry, struct nameidata *nd)
> +{
> + int status = dentry->d_op->d_revalidate(dentry, nd);
> + if (unlikely(status <= 0)) {

d_revalidate() returns a 0 or 1 result, not an error.

> + /*
> + * The dentry failed validation.
> + * If d_revalidate returned 0 attempt to invalidate
> + * the dentry otherwise d_revalidate is asking us
> + * to return a fail status.
> + */
> + if (!status) {
> + if (!d_invalidate(dentry)) {
> + __dput_single(dentry);
> + dentry = NULL;
> + }
> + } else {
> + __dput_single(dentry);
> + dentry = ERR_PTR(status);

See above

> + }
> + }
> + return dentry;
> +}
> +
> +/*
> + * FIXME: We need a union aware revalidate here!
> + */
> +static inline struct dentry *
> do_revalidate(struct dentry *dentry, struct nameidata *nd)
> {
> int status = dentry->d_op->d_revalidate(dentry, nd);
> @@ -403,16 +430,16 @@ do_revalidate(struct dentry *dentry, str
> */
> static struct dentry * cached_lookup(struct dentry * parent, struct qstr * name, struct nameidata *nd)
> {
> - struct dentry * dentry = __d_lookup(parent, name);
> + struct dentry *dentry = __d_lookup_single(parent, name);
>
> /* lockess __d_lookup may fail due to concurrent d_move()
> * in some unrelated directory, so try with d_lookup
> */
> if (!dentry)
> - dentry = d_lookup(parent, name);
> + dentry = d_lookup_single(parent, name);
>
> if (dentry && dentry->d_op && dentry->d_op->d_revalidate)
> - dentry = do_revalidate(dentry, nd);
> + dentry = do_revalidate_single(dentry, nd);
>
> return dentry;
> }
> @@ -465,7 +492,7 @@ ok:
> * make sure that nobody added the entry to the dcache in the meantime..
> * SMP-safe
> */
> -static struct dentry * real_lookup(struct dentry * parent, struct qstr * name, struct nameidata *nd)
> +struct dentry * real_lookup_single(struct dentry *parent, struct qstr *name, struct nameidata *nd)
> {
> struct dentry * result;
> struct inode *dir = parent->d_inode;
> @@ -485,7 +512,7 @@ static struct dentry * real_lookup(struc
> *
> * so doing d_lookup() (with seqlock), instead of lockfree __d_lookup
> */
> - result = d_lookup(parent, name);
> + result = d_lookup_single(parent, name);
> if (!result) {
> struct dentry * dentry = d_alloc(parent, name);
> result = ERR_PTR(-ENOMEM);
> @@ -506,7 +533,7 @@ static struct dentry * real_lookup(struc
> */
> mutex_unlock(&dir->i_mutex);
> if (result->d_op && result->d_op->d_revalidate) {
> - result = do_revalidate(result, nd);
> + result = do_revalidate_single(result, nd);
> if (!result)
> result = ERR_PTR(-ENOENT);
> }
> @@ -699,7 +726,7 @@ static int __follow_mount(struct path *p
> return res;
> }
>
> -static void follow_mount(struct vfsmount **mnt, struct dentry **dentry)
> +void follow_mount(struct vfsmount **mnt, struct dentry **dentry)
> {
> while (d_mountpoint(*dentry)) {
> struct vfsmount *mounted = lookup_mnt(*mnt, *dentry);
> @@ -773,6 +800,7 @@ static __always_inline void follow_dotdo
> nd->mnt = parent;
> }
> follow_mount(&nd->mnt, &nd->dentry);
> + follow_union_mount(&nd->mnt, &nd->dentry);
> }
>
> /*
> @@ -784,7 +812,15 @@ static int do_lookup(struct nameidata *n
> struct path *path)
> {
> struct vfsmount *mnt = nd->mnt;
> - struct dentry *dentry = __d_lookup(nd->dentry, name);
> + struct dentry *dentry;
> +
> + UM_DEBUG_UID("lookup \"%s\" in \"%s\" (inode=%p,dev=%s)\n",
> + name->name,
> + nd->dentry->d_name.name,
> + nd->dentry->d_inode,
> + nd->mnt->mnt_devname);

Ugh! Please don't pollute generic VFS code with this sort of private
debugging crap.

> +
> + dentry = __d_lookup(nd->dentry, name);
>
> if (!dentry)
> goto need_lookup;
> @@ -793,7 +829,17 @@ static int do_lookup(struct nameidata *n
> done:
> path->mnt = mnt;
> path->dentry = dentry;
> +
> + if (nd->dentry->d_sb != dentry->d_sb)
> + path->mnt = find_mnt(dentry);
> +
> __follow_mount(path);
> + follow_union_mount(&path->mnt, &path->dentry);
> +
> + UM_DEBUG_UID("found \"%s\" (inode=%p,dev=%s)\n",
> + path->dentry->d_name.name,
> + path->dentry->d_inode,
> + path->mnt->mnt_devname);
> return 0;
>
> need_lookup:
> @@ -838,6 +884,9 @@ static fastcall int __link_path_walk(con
> if (nd->depth)
> lookup_flags = LOOKUP_FOLLOW | (nd->flags & LOOKUP_CONTINUE);
>
> + UM_DEBUG_UID("begin walking for %s\n", name);
> + follow_union_mount(&nd->mnt, &nd->dentry);
> +
> /* At this point we know we have a real path component. */
> for(;;) {
> unsigned long hash;
> @@ -931,6 +980,7 @@ static fastcall int __link_path_walk(con
> last_with_slashes:
> lookup_flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
> last_component:
> + UM_DEBUG_UID("last component %s\n", this.name);
> /* Clear LOOKUP_CONTINUE iff it was previously unset */
> nd->flags &= lookup_flags | ~LOOKUP_CONTINUE;
> if (lookup_flags & LOOKUP_PARENT)
> @@ -1266,7 +1316,15 @@ int __user_path_lookup_open(const char _
> return err;
> }
>
> -static inline struct dentry *__lookup_hash_kern(struct qstr *name, struct dentry *base, struct nameidata *nd)
> +/*
> + * NOTE: On union mounts it is important that the overlaid dentries are
> + * correct. Therefore we need to follow mounts. Take a look at
> + * __lookup_hash_kern_union() how it is done.
> + *
> + * Called with union already locked (before the parent inode is locked !!!)
> + */
> +struct dentry * __lookup_hash_kern_single(struct qstr *name,
> + struct dentry *base, struct nameidata *nd)
> {
> struct dentry *dentry;
> struct inode *inode;
> @@ -1298,6 +1356,8 @@ static inline struct dentry *__lookup_ha
> dput(new);
> }
> out:
> + UM_DEBUG_UID("name=\"%s\", inode=%p\n",
> + dentry->d_name.name, dentry->d_inode);
> return dentry;
> }
>
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -133,6 +133,41 @@ struct vfsmount *lookup_mnt(struct vfsmo
> return child_mnt;
> }
>
> +/*
> + * find_mnt - find a vfsmount struct
> + * @dentry: a dentry
> + *
> + * This searches the namespace for a given dentries
> + * vfsmount struct. This is used by union-mount.
> + */
> +struct vfsmount * find_mnt(struct dentry *dentry)
> +{
> + struct list_head *tmp;
> + struct vfsmount *p, *mnt = NULL;
> +
> + down_read(&namespace_sem);
> + spin_lock(&vfsmount_lock);
> + if (list_empty(&current->nsproxy->mnt_ns->list)) {
> + spin_unlock(&vfsmount_lock);
> + up_read(&namespace_sem);
> + return NULL;
> + }
> + list_for_each(tmp, &current->nsproxy->mnt_ns->list) {
> + p = list_entry(tmp, struct vfsmount, mnt_list);
> + if (dentry->d_sb == p->mnt_sb) {
> + mnt = mntget(p);
> + break;
> + }
> + }
> + spin_unlock(&vfsmount_lock);
> + up_read(&namespace_sem);
> +
> + BUG_ON(!mnt);
> +// UM_DEBUG_UID("found %s/%p in %s\n", dentry->d_name.name,
> +// dentry->d_inode, mnt->mnt_devname);

^^^^ Definitely remove

> + return mnt;
> +}
> +
> static inline int check_mnt(struct vfsmount *mnt)
> {
> return mnt->mnt_ns == current->nsproxy->mnt_ns;
> --- a/fs/union.c
> +++ b/fs/union.c
> @@ -370,3 +370,601 @@ void detach_mnt_union(struct vfsmount *m
> * union stack */
> __dput(path->dentry);
> }
> +
> +static noinline int revalidate_union(struct dentry * dentry)
^^^^^^^^ this is just as bad as 'inline'. I thought we had all
agreed to leave it up to the compiler to optimise.
> +{
> + union_check(dentry);
> +
> + spin_lock(&dcache_lock);
> + spin_lock(&dentry->d_lock);
> + if (atomic_read(&dentry->d_count) < 2) {
> + UM_DEBUG_DCACHE("dentry unused, count=%d\n",
> + atomic_read(&dentry->d_count));
> + __d_drop(dentry);
> + spin_unlock(&dentry->d_lock);
> + spin_unlock(&dcache_lock);
> + return 0;
> + }
> + spin_unlock(&dentry->d_lock);
> + spin_unlock(&dcache_lock);
> +
> + return 1;
> +}
> +
> +static noinline void replace_union_info(struct dentry *dentry,
> + struct union_info *lock)
> +{
> + struct dentry *tmp = dentry;
> + struct union_info *old_lock = union_get(dentry->d_union);
> +
> + BUG_ON(!lock);
> + BUG_ON(dentry->d_union == lock);
> +
> + while (tmp) {
> + spin_lock(&tmp->d_lock);
> + union_put(tmp->d_union);
> + tmp->d_union = union_get(lock);
> + spin_unlock(&tmp->d_lock);
> + tmp = tmp->d_overlaid;
> + }
> +
> + BUG_ON(atomic_read(&old_lock->u_count) != 1);
> + union_put(old_lock);
> + return;
> +}
> +
> +static void __dput_from_to(struct dentry *from, struct dentry *to,
> + struct union_info *lock)
> +{
> + struct dentry *next = from;
> + struct union_info *mylock = union_get(from->d_union);
> +
> + while (next) {
> + struct dentry *tmp = next;
> + next = next->d_overlaid;
> +
> + UM_DEBUG_UID("dput_all dentry=\"%s\", inode=\"%p\"\n",
> + tmp->d_name.name, tmp->d_inode);
> +
> + if (lock) {
> + spin_lock(&tmp->d_lock);
> + tmp->d_topmost = NULL;
> + tmp->d_overlaid = NULL;
> + union_put(tmp->d_union);
> + tmp->d_union = NULL;
> + spin_unlock(&tmp->d_lock);
> + }
> +
> + __dput_single(tmp);
> +
> + if (tmp == to)
> + break;
> + }
> +
> + UM_DEBUG_LOCK("\"??\" unlocking union %p\n", lock);
> + mutex_unlock(&mylock->u_mutex);
> + union_put(mylock);
> +}
> +
> +/*
> + * Lookup for the @name in the dentry cache. Look through the lower layers
> + * of the parent's union stack and build a union stack for the child if
> + * necessary.
> + * TODO: This shares a considerable amount of code with __lookup_union().
> + */
> +struct dentry * __d_lookup_union(struct dentry *base, struct qstr *name)
> +{
> + struct dentry *parent = base->d_overlaid;
> + struct dentry *dentry = NULL;
> + struct dentry *topmost;
> + struct dentry *last;
> + struct qstr this;
> + struct union_info *lock = NULL;
> + int err;
> +
> + union_lock(base);
> + topmost = __d_lookup_single(base, name);
> + last = topmost;
> +
> + /*
> + * - If dcache lookup returns a NULL dentry, return to force a real
> + * lookup. Union mount version of real lookup will endup doing real or
> + * dcache lookup for this in the lower layers also. OR
> + * - If parent is not a union mounted directory, we are done
> + * with the lookup, return.
> + */
> + if (!topmost || !base->d_overlaid)
> + goto out;
> +
> + this.name = name->name;
> + this.len = name->len;
> + this.hash = name->hash;
> +
> + /*
> + * If dcache lookup returned a non-negative dentry from the top layer,
> + * continue the lookup in to the lower layers and re-build the union
> + * stack if necessary.
> + */
> + if (topmost->d_inode)
> + goto lookup_union;
> +
> + /*
> + * dcache lookup in the top layer returned a negative dentry. Look
> + * through the lower layers to find the first non-negative dentry.
> + */
> + while (parent) {
> + if (parent->d_op && parent->d_op->d_hash) {
> + err = parent->d_op->d_hash(parent, &this);
> + if (err < 0) {
> + __dput_single(topmost);
> + topmost = NULL;
> + goto out;
> + }
> + }
> + dentry = __d_lookup_single(parent, &this);
> + /*
> + * Force a real lookup if parts of the union stack are not in
> + * dcache
> + */
> + if (!dentry) {
> + __dput_single(topmost);
> + topmost = NULL;
> + goto out;
> + }
> + if (dentry->d_inode)
> + break;
> + __dput_single(dentry);
> + dentry = NULL;
> + parent = parent->d_overlaid;
> + }
> +
> + if (!dentry)
> + goto out;
> +
> + __dput_single(topmost);
> + topmost = dentry;
> + last = dentry;
> +lookup_union:
> + do {
> + struct vfsmount *mnt = find_mnt(topmost);
> + UM_DEBUG_DCACHE("name=\"%s\", inode=%p, device=%s\n",
> + topmost->d_name.name, topmost->d_inode,
> + mnt->mnt_devname);
> + mntput(mnt);
> + } while (0);
> +
> + /* If this is not a directory, no need to look beyond this layer */
> + if (!S_ISDIR(topmost->d_inode->i_mode))
> + goto out;
> +
> + if (!revalidate_union(topmost)) {
> + __dput_single(topmost);
> + topmost = NULL;
> + goto out;
> + }
> +
> + spin_lock(&topmost->d_lock);
> + if (topmost->d_union) {
> + union_lock_spinlock(topmost, &topmost->d_lock);
> + }
> + spin_unlock(&topmost->d_lock);
> +
> + parent = topmost->d_parent->d_overlaid;
> + while (parent) {
> + if (parent->d_op && parent->d_op->d_hash) {
> + err = parent->d_op->d_hash(parent, &this);
> + if (err < 0) {
> + UM_DEBUG("failed to hash the qstr\n");
> + goto dput_all;
> + }
> + }
> + dentry = __d_lookup_single(parent, &this);
> + if (!dentry) {
> + /*
> + * No dentry for this name in this lower layer.
> + * CHECK: Why return like this ? Shoudn't we look
> + * for this name in the next lower layer ?
> + */
> + __dput_single(dentry);
> + goto dput_all;
> + }
> +
> + if (!dentry->d_inode) {
> + __dput_single(dentry);
> + parent = parent->d_overlaid;
> + continue;
> + }
> + if (!S_ISDIR(dentry->d_inode->i_mode)) {
> + __dput_single(dentry);
> + break;
> + }
> + if (last->d_overlaid
> + && (last->d_overlaid != dentry)) {
> + printk(KERN_ERR "%s: strange stack layout " \
> + "(\"%s\" overlays \"%s\")\n",
> + __FUNCTION__, last->d_name.name,
> + dentry->d_name.name);
> + dump_stack();
> + __dput_single(dentry);
> + goto dput_all;
> + }
> + spin_lock(&topmost->d_lock);
> + if (!topmost->d_union) {
> + UM_DEBUG_LOCK("allocate union for \"%s\"\n",
> + topmost->d_name.name);
> + topmost->d_union = union_alloc();
> + lock = topmost->d_union;
> + }
> + spin_unlock(&topmost->d_lock);
> + spin_lock(&dentry->d_lock);
> + if (!dentry->d_union)
> + dentry->d_union = union_get(topmost->d_union);
> + spin_unlock(&dentry->d_lock);
> + if (dentry->d_union != topmost->d_union) {
> + union_lock(dentry);
> + replace_union_info(topmost, dentry->d_union);
> + }
> + dentry->d_topmost = topmost;
> + last->d_overlaid = dentry;
> + last = dentry;
> + parent = parent->d_overlaid;
> + }
> +
> + spin_lock(&topmost->d_lock);
> + if (topmost->d_union && atomic_read(&topmost->d_union->u_count) == 1) {
> + union_put(topmost->d_union);
> + topmost->d_union = NULL;
> + } else
> + union_unlock(topmost);
> + spin_unlock(&topmost->d_lock);
> +out:
> + union_unlock(base);
> + return topmost;
> +
> +dput_all:
> + __dput_from_to(topmost, last, lock);
> + union_unlock(base);
> + return NULL;
> +}
> +
> +/*
> + * FIXME: export this from fs/namei.c ???
> + */
> +extern int follow_mount(struct vfsmount **, struct dentry **);
> +extern struct dentry * __lookup_hash_kern_single(struct qstr *, struct dentry *,
> + struct nameidata *);
> +extern struct dentry * real_lookup_single(struct dentry *, struct qstr *,
> + struct nameidata *);
> +
> +static inline void copy_nd(struct nameidata *old_nd, struct nameidata *new_nd)
> +{
> + if (old_nd) {
> + new_nd->last.name = NULL; /* handled in __link_path_walk */
> + new_nd->last.len = 0;
> + new_nd->last.hash = 0;
> + new_nd->flags = old_nd->flags;
> + new_nd->um_flags = 0; /* ditto */
> + new_nd->last_type = -1; /* ditto */
> + new_nd->depth = 0; /* handled in do_follow_link */
> + memcpy(&new_nd->intent, &old_nd->intent, sizeof(new_nd->intent));
> + }
> +}
> +
> +/*
> + * This is called when a dentries parent is union-mounted and we have
> + * to lookup the overlaid dentries. The lookup starts at the parents
> + * first overlaid dentry of the given dentry. Negative dentries are
> + * ignored and not included in the overlaid list.
> + *
> + * If we reach a dentry with restricted access, we just stop the lookup
> + * because we shouldn't see through that dentry. Same thing for dentry
> + * type mismatch and whiteouts.
> + *
> + * FIXME:
> + * - handle DT_WHT
> + * - handle union stacks in use
> + * - handle union stacks mounted upon union stacks
> + * - avoid unnecessary allocations of union locks
> + */
> +static int __lookup_union(struct dentry *topmost, struct qstr *name,
> + struct nameidata *__nd)
> +{
> + struct dentry *parent;
> + struct dentry *last;
> + struct dentry *dentry;
> + unsigned int hash = name->hash;
> + struct nameidata nd;
> + int err;
> +
> + /* we may also be called via lookup_hash with a NULLed nd argument */
> + copy_nd(__nd, &nd);
> +
> + spin_lock(&topmost->d_lock);
> + if (topmost->d_union) {
> + union_lock_spinlock(topmost, &topmost->d_lock);
> + }
> + spin_unlock(&topmost->d_lock);
> +
> + parent = topmost->d_parent->d_overlaid;
> + last = topmost;
> +
> + while (parent) {
> + /*
> + * the hash could be changed in the last
> + * __lookup_hash_single() so we need to reset it here
> + */
> + name->hash = hash;
> + nd.dentry = __dget(parent);
> + nd.mnt = find_mnt(parent);
> +
> + mutex_lock(&parent->d_inode->i_mutex);
> + dentry = __lookup_hash_single(name, parent,
> + __nd ? &nd : NULL);
> + mutex_unlock(&parent->d_inode->i_mutex);
> + if (IS_ERR(dentry)) {
> + err = PTR_ERR(dentry);
> + goto out;
> + }
> +
> + if (!dentry->d_inode) {
> + __dput_single(dentry);
> + goto loop;
> + }
> +
> + if (!S_ISDIR(dentry->d_inode->i_mode)) {
> + __dput_single(dentry);
> + err = 0;
> + goto out;
> + }
> +
> + /* Now we know, we found something real */
> + follow_mount(&nd.mnt, &dentry);
> +
> + do {
> + struct vfsmount *mnt = find_mnt(dentry);
> + UM_DEBUG_UID("name=\"%s\", inode=%p, device=%s\n",
> + dentry->d_name.name, dentry->d_inode,
> + mnt->mnt_devname);
> + mntput(mnt);
> + } while (0);
> +
> + if (last->d_overlaid && (last->d_overlaid != dentry)) {
> + printk(KERN_ERR "%s: strange stack layout " \
> + "(\"%s\" overlays \"%s\")\n",
> + __FUNCTION__, last->d_name.name,
> + dentry->d_name.name);
> + dump_stack();
> + __dput_single(dentry);
> + /* lets try to make a clean ending */
> + last->d_overlaid = NULL;
> + err = -EFAULT; // FIXME: something better?
> + goto out;
> + }
> +
> + spin_lock(&topmost->d_lock);
> + if (!topmost->d_union) {
> + UM_DEBUG_LOCK("allocate union for \"%s\"\n",
> + topmost->d_name.name);
> + topmost->d_union = union_alloc();
> + }
> + spin_unlock(&topmost->d_lock);
> +
> + spin_lock(&dentry->d_lock);
> + if (!dentry->d_union)
> + dentry->d_union = union_get(topmost->d_union);
> + spin_unlock(&dentry->d_lock);
> +
> + if (topmost->d_union != dentry->d_union) {
> + union_lock(dentry);
> + replace_union_info(topmost, dentry->d_union);
> + }
> +
> + dentry->d_topmost = topmost;
> + last->d_overlaid = dentry;
> + last = dentry;
> + loop:
> + __dput(nd.dentry);
> + mntput(nd.mnt);
> + parent = parent->d_overlaid;
> + }
> +
> + err = 0;
> + union_unlock(topmost);
> + return err;
> +out:
> + __dput(nd.dentry);
> + mntput(nd.mnt);
> + union_unlock(topmost);
> + return err;
> +}
> +
> +/*
> + * Union mount version of real_lookup().
> + * Looks through the lower layers of the union and builds a union stack
> + * if necessary (i,e., for directories)
> + * TODO: This routine is almost similar to __lookup_hash_kern_union() which
> + * uses __lookup_hash_kern_single() (instead of real_lookup_single()). Check
> + * if some code can be shared here.
> + */
> +struct dentry * real_lookup_union(struct dentry *base, struct qstr *name,
> + struct nameidata *__nd)
> +{
> + struct dentry *parent;
> + struct dentry *topmost;
> + unsigned int hash = name->hash;
> + struct nameidata nd;
> + int err;
> +
> + union_lock(base);
> + topmost = real_lookup_single(base, name, __nd);
> + if (IS_ERR(topmost))
> + goto out;
> +
> + /*
> + * If real_lookup returns a valid dentry from the topmost layer,
> + * continue the lookup into the lower layers and build a union
> + * stack in case of directories.
> + */
> + if (topmost->d_inode) {
> + parent = base;
> + goto lookup_union;
> + }
> +
> + copy_nd(__nd, &nd);
> +
> + /*
> + * real_lookup returned a negative dentry, walk through the lower
> + * layers looking for the given name.
> + */
> + parent = base->d_overlaid;
> + while (parent) {
> + struct dentry * dentry;
> +
> + name->hash = hash;
> + nd.dentry = __dget(parent);
> + nd.mnt = find_mnt(parent);
> +
> + dentry = real_lookup_single(nd.dentry, name, &nd);
> + __dput(nd.dentry);
> + mntput(nd.mnt);
> + if (IS_ERR(dentry))
> + goto out;
> +
> + /*
> + * If a dentry is found in a lower layer, continue to lookup
> + * in the lower layers and build a union stack if needed.
> + */
> + if (dentry->d_inode) {
> + __dput_single(topmost);
> + topmost = dentry;
> + goto lookup_union;
> + }
> + __dput_single(dentry);
> + parent = parent->d_overlaid;
> + }
> +
> +out:
> + union_unlock(base);
> + return topmost;
> +
> +lookup_union:
> + /*
> + * If our parent doesn't have a union stack or we are not a directory,
> + * the lookup ends here.
> + */
> + if (!parent->d_overlaid || !S_ISDIR(topmost->d_inode->i_mode))
> + goto out;
> +
> + do {
> + struct vfsmount *mnt = find_mnt(topmost);
> + UM_DEBUG_UID("name=\"%s\", inode=%p, device=%s\n",
> + topmost->d_name.name, topmost->d_inode,
> + mnt->mnt_devname);
> + mntput(mnt);
> + } while (0);
> +
> + name->hash = hash;
> + err = __lookup_union(topmost, name, &nd);
> + if (err) {
> + dput(topmost);
> + topmost = ERR_PTR(err);
> + }
> + goto out;
> +}
> +
> +/*
> + * Union mount version of __lookup_hash_kern().
> + * Looks through the lower layers of the union and builds a union stack
> + * if necessary (i,e., for directories)
> + */
> +struct dentry * __lookup_hash_kern_union(struct qstr *name,
> + struct dentry *base, struct nameidata *__nd)
> +{
> + struct dentry *topmost;
> + struct dentry *parent;
> + unsigned int hash = name->hash;
> + struct nameidata nd;
> + int err;
> +
> + union_lock(base);
> + topmost = __lookup_hash_kern_single(name, base, __nd);
> + if (IS_ERR(topmost))
> + goto out;
> +
> + if (topmost->d_inode) {
> + parent = base;
> + goto lookup_union;
> + }
> +
> + copy_nd(__nd, &nd);
> +
> + parent = base->d_overlaid;
> + while (parent) {
> + struct dentry *dentry;
> +
> + name->hash = hash;
> + nd.dentry = __dget(parent);
> + nd.mnt = find_mnt(parent);
> +
> + mutex_lock(&parent->d_inode->i_mutex);
> + dentry = __lookup_hash_kern_single(name, nd.dentry, &nd);
> + mutex_unlock(&parent->d_inode->i_mutex);
> + __dput(nd.dentry);
> + mntput(nd.mnt);
> + if (IS_ERR(dentry))
> + goto out;
> +
> + if (dentry->d_inode) {
> + __dput_single(topmost);
> + topmost = dentry;
> + goto lookup_union;
> + }
> + __dput_single(dentry);
> + parent = parent->d_overlaid;
> + }
> +
> +out:
> + union_unlock(base);
> + return topmost;
> +
> +lookup_union:
> + if (!parent->d_overlaid || !S_ISDIR(topmost->d_inode->i_mode))
> + goto out;
> +
> + do {
> + struct vfsmount *mnt = find_mnt(topmost);
> + UM_DEBUG_UID("name=\"%s\", inode=%p, device=%s\n",
> + topmost->d_name.name, topmost->d_inode,
> + mnt->mnt_devname);
> + mntput(mnt);
> + } while (0);
> +
> + name->hash = hash;
> + err = __lookup_union(topmost, name, &nd);
> + if (err) {
> + dput(topmost);
> + topmost = ERR_PTR(err);
> + }
> + goto out;
> +}
> +
> +int follow_union_mount(struct vfsmount **mnt, struct dentry **dentry)
> +{
> + int res = 0;
> +
> + while ((*dentry)->d_topmost) {
> + struct dentry *d_tmp = dget((*dentry)->d_topmost);
> + struct vfsmount *m_tmp = find_mnt((*dentry)->d_topmost);
> +
> + UM_DEBUG_UID("name=\"%s\", follow union from %s to %s\n",
> + (*dentry)->d_name.name, (*mnt)->mnt_devname,
> + m_tmp->mnt_devname);
> + mntput(*mnt);
> + *mnt = m_tmp;
> + dput(*dentry);
> + *dentry = d_tmp;
> + res = 1;
> + }
> +
> + return res;
> +}
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -294,9 +294,23 @@ extern void d_move(struct dentry *, stru
>
> /* appendix may either be NULL or be used for transname suffixes */
> extern struct dentry * d_lookup(struct dentry *, struct qstr *);
> -extern struct dentry * __d_lookup(struct dentry *, struct qstr *);
> +extern struct dentry * d_lookup_single(struct dentry *, struct qstr *);
> +extern struct dentry * __d_lookup_single(struct dentry *, struct qstr *);
> extern struct dentry * d_hash_and_lookup(struct dentry *, struct qstr *);
>
> +#ifdef CONFIG_UNION_MOUNT
> +extern struct dentry * __d_lookup_union(struct dentry *, struct qstr *);
> +#endif
> +
> +static inline struct dentry * __d_lookup(struct dentry *parent, struct qstr *name)
> +{
> +#ifdef CONFIG_UNION_MOUNT
> + return __d_lookup_union(parent, name);
> +#else
> + return __d_lookup_single(parent, name);
> +#endif
> +}
> +
> /* validate "insecure" dentry pointer */
> extern int d_validate(struct dentry *, struct dentry *);
>
> @@ -467,6 +481,7 @@ static inline int d_mountpoint(struct de
> extern struct vfsmount *lookup_mnt(struct vfsmount *, struct dentry *);
> extern struct vfsmount *__lookup_mnt(struct vfsmount *, struct dentry *, int);
> extern struct dentry *lookup_create(struct nameidata *nd, int is_dir);
> +extern struct vfsmount *find_mnt(struct dentry *);
>
> extern int sysctl_vfs_cache_pressure;
>
> --- a/include/linux/namei.h
> +++ b/include/linux/namei.h
> @@ -20,6 +20,7 @@ struct nameidata {
> struct vfsmount *mnt;
> struct qstr last;
> unsigned int flags;
> + unsigned int um_flags;
> int last_type;
> unsigned depth;
> char *saved_names[MAX_NESTED_LINKS + 1];
> @@ -40,6 +41,9 @@ struct path {
> */
> enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND};
>
> +#define LAST_UNION 0x01
> +#define LAST_LOWLEVEL 0x02
> +
> /*
> * The bitmask for a lookup event:
> * - follow links at the end
> --- a/include/linux/union.h
> +++ b/include/linux/union.h
> @@ -17,17 +17,66 @@
> #ifdef CONFIG_UNION_MOUNT
>
> #include <linux/fs_struct.h>
> +#include <linux/dcache_union.h>
>
> /* namespace stuff used at mount time */
> extern void attach_mnt_union(struct vfsmount *, struct nameidata *);
> extern void detach_mnt_union(struct vfsmount *, struct path *);
>
> +/* lookup stuff */
> +extern int follow_union_mount(struct vfsmount **, struct dentry **);
> +extern struct dentry * real_lookup_union(struct dentry *, struct qstr *,
> + struct nameidata *);
> +extern struct dentry * __lookup_hash_kern_union(struct qstr *, struct dentry *,
> + struct nameidata *);
> +
> #else /* CONFIG_UNION_MOUNT */
>
> #define attach_mnt_union(mnt,nd) do { /* empty */ } while (0)
> #define detach_mnt_union(mnt,nd) do { /* empty */ } while (0)
> +#define follow_union_mount(x,y) do { /* empty */ } while (0)
>
> #endif /* CONFIG_UNION_MOUNT */
>
> +extern struct dentry * real_lookup_single(struct dentry *, struct qstr *,
> + struct nameidata *);
> +extern struct dentry * __lookup_hash_kern_single(struct qstr *, struct dentry *,
> + struct nameidata *);
> +
> +static inline struct dentry * real_lookup(struct dentry *parent, struct qstr *name, struct nameidata *nd)
> +{
> +#ifdef CONFIG_UNION_MOUNT
> + return real_lookup_union(parent, name, nd);
> +#else
> + return real_lookup_single(parent, name, nd);
> +#endif
> +}
> +
> +static inline struct dentry * __lookup_hash_kern(struct qstr *name, struct dentry *base, struct nameidata *nd)
> +{
> +#ifdef CONFIG_UNION_MOUNT
> + return __lookup_hash_kern_union(name, base, nd);
> +#else
> + return __lookup_hash_kern_single(name, base, nd);
> +#endif
> +}
> +
> +static inline struct dentry * __lookup_hash_single(struct qstr *name, struct dentry *base, struct nameidata *nd)
> +{
> + struct dentry *dentry;
> + struct inode *inode;
> + int err;
> +
> + inode = base->d_inode;
> +
> + err = permission(inode, MAY_EXEC, nd);
> + dentry = ERR_PTR(err);
> + if (err)
> + goto out;
> +
> + dentry = __lookup_hash_kern_single(name, base, nd);
> +out:
> + return dentry;
> +}
> #endif /* __KERNEL __ */
> #endif /* __LINUX_UNION_H */
> -
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