[PATCH 41/41] union-mount: Add support for rename by __union_copyup()

From: Valerie Aurora
Date: Wed Oct 21 2009 - 15:22:52 EST

From: Jan Blunck <jblunck@xxxxxxxxxxxxx>

It is possible to use __union_copyup() to support rename of regular files
without returning -EXDEV.

XXX - Rewrite as copyup to old name followed by rename() + whiteout()

Signed-off-by: Jan Blunck <jblunck@xxxxxxxxxxxxx>
Signed-off-by: Valerie Aurora <vaurora@xxxxxxxxxx>
---
fs/namei.c | 350 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 344 insertions(+), 6 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index e3e8e98..8419e1e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1842,6 +1842,239 @@ out:
return res;
}

+/**
+ * do_union_hash_lookup() - walk down the union stack and lookup_hash()
+ * @nd: nameidata of parent to lookup from
+ * @name: pathname component to lookup
+ * @path: path to store result of lookup in
+ *
+ * Walk down the union stack and search for single pathname component name. It
+ * is assumed that the caller already did a lookup_hash() in the topmost parent
+ * that gave negative lookup result. Therefore this does call lookup_hash() in
+ * every lower layer (!) of the union stack. If a directory is found the union
+ * stack for that is assembled as well.
+ *
+ * Note:
+ * The caller needs to take care of holding a valid reference to the topmost
+ * parent.
+ * On error we leave @path untouched as well as when we don't find anything.
+ */
+static int do_union_hash_lookup(struct nameidata *nd, struct qstr *name,
+ struct path *path)
+{
+ struct path next;
+ int err = 0;
+
+ while (follow_union_down(&nd->path.mnt, &nd->path.dentry)) {
+ /* rehash because of d_op->d_hash() by the previous layer */
+ name->hash = full_name_hash(name->name, name->len);
+
+ mutex_lock(&nd->path.dentry->d_inode->i_mutex);
+ err = lookup_hash(nd, name, &next);
+ mutex_unlock(&nd->path.dentry->d_inode->i_mutex);
+
+ if (err)
+ break;
+
+ if (next.dentry->d_inode) {
+ mntget(next.mnt);
+ if (!S_ISDIR(next.dentry->d_inode->i_mode)) {
+ *path = next;
+ break;
+ }
+ err = __hash_lookup_build_union(nd, name, &next);
+ if (err)
+ path_put(&next);
+ else
+ *path = next;
+ break;
+ }
+
+ path_put_conditional(&next, nd);
+
+ if ((IS_OPAQUE(nd->path.dentry->d_inode) &&
+ !d_is_fallthru(next.dentry)) ||
+ d_is_whiteout(next.dentry))
+ break;
+ }
+
+ return err;
+}
+
+/**
+ * _hash_lookup_union() - lookup single pathname component
+ * @nd: nameidata of parent to lookup from
+ * @name: pathname component to lookup
+ * @path: path to store result of lookup in
+ *
+ * Returns the topmost parent locked and the target dentry found in the union
+ * or the topmost negative target dentry otherwise.
+ *
+ * Note:
+ * Returns topmost parent locked even on error.
+ */
+static int _hash_lookup_union(struct nameidata *nd, struct qstr *name,
+ struct path *path)
+{
+ struct path parent = nd->path;
+ struct path topmost;
+ int err;
+
+ mutex_lock(&nd->path.dentry->d_inode->i_mutex);
+ err = lookup_hash(nd, name, path);
+ if (err)
+ return err;
+
+ /* return if we found something and it isn't a directory we are done */
+ if (path->dentry->d_inode && !S_ISDIR(path->dentry->d_inode->i_mode))
+ return 0;
+
+ /* stop lookup if the parent directory is marked opaque */
+ if ((IS_OPAQUE(nd->path.dentry->d_inode) &&
+ !d_is_fallthru(path->dentry)) ||
+ d_is_whiteout(path->dentry))
+ return 0;
+
+ if (!strcmp(path->mnt->mnt_sb->s_type->name, "proc") ||
+ !strcmp(path->mnt->mnt_sb->s_type->name, "sysfs"))
+ return 0;
+
+ mutex_unlock(&nd->path.dentry->d_inode->i_mutex);
+
+ /*
+ * safe a reference to the topmost parent for walking the union stack
+ */
+ path_get(&parent);
+ topmost = *path;
+
+ if (path->dentry->d_inode && S_ISDIR(path->dentry->d_inode->i_mode)) {
+ err = __hash_lookup_build_union(nd, name, path);
+ if (err)
+ goto err_lock_parent;
+ goto out_lock_and_revalidate_parent;
+ }
+
+ err = do_union_hash_lookup(nd, name, path);
+ if (err)
+ goto err_lock_parent;
+
+out_lock_and_revalidate_parent:
+ /* seems that we haven't found anything, so return the topmost */
+ path_to_nameidata(&parent, nd);
+ mutex_lock(&nd->path.dentry->d_inode->i_mutex);
+
+ if (topmost.dentry == path->dentry) {
+ spin_lock(&path->dentry->d_lock);
+ if (nd->path.dentry != path->dentry->d_parent) {
+ spin_unlock(&path->dentry->d_lock);
+ dput(path->dentry);
+ name->hash = full_name_hash(name->name, name->len);
+ err = lookup_hash(nd, name, path);
+ if (err)
+ return err;
+ /* FIXME: What if we find a directory here ... */
+ return err;
+ }
+ spin_unlock(&path->dentry->d_lock);
+ } else
+ dput(topmost.dentry);
+
+ return 0;
+
+err_lock_parent:
+ path_to_nameidata(&parent, nd);
+ path_put_conditional(path, nd);
+ mutex_lock(&nd->path.dentry->d_inode->i_mutex);
+ return err;
+}
+
+/**
+ * lookup_rename_source() - lookup the source used by rename
+ *
+ * This is a special version of _hash_lookup_union() which becomes necessary
+ * for finding the source of a rename on union mounts.
+ *
+ * See comment for _hash_lookup_union() above.
+ */
+static int lookup_rename_source(struct nameidata *oldnd,
+ struct nameidata *newnd,
+ struct dentry **trap, struct qstr *name,
+ struct path *old)
+{
+ struct path parent = oldnd->path;
+ struct path topmost;
+ int err;
+
+ err = lookup_hash(oldnd, name, old);
+ if (err)
+ return err;
+
+ /* return if we found something and it isn't a directory we are done */
+ if (old->dentry->d_inode && !S_ISDIR(old->dentry->d_inode->i_mode))
+ return 0;
+
+ /* stop lookup if the parent directory is marked opaque */
+ if ((IS_OPAQUE(oldnd->path.dentry->d_inode) &&
+ !d_is_fallthru(old->dentry)) ||
+ d_is_whiteout(old->dentry))
+ return 0;
+
+ if (!strcmp(old->mnt->mnt_sb->s_type->name, "proc") ||
+ !strcmp(old->mnt->mnt_sb->s_type->name, "sysfs"))
+ return 0;
+
+ unlock_rename(oldnd->path.dentry, newnd->path.dentry);
+
+ /*
+ * safe a reference to the topmost parent for walking the union stack
+ */
+ path_get(&parent);
+ topmost = *old;
+
+ if (old->dentry->d_inode && S_ISDIR(old->dentry->d_inode->i_mode)) {
+ err = __hash_lookup_build_union(oldnd, name, old);
+ if (err)
+ goto err_lock;
+ goto out_lock_and_revalidate_parent;
+ }
+
+ err = do_union_hash_lookup(oldnd, name, old);
+ if (err)
+ goto err_lock;
+
+out_lock_and_revalidate_parent:
+ path_to_nameidata(&parent, oldnd);
+ *trap = lock_rename(oldnd->path.dentry, newnd->path.dentry);
+
+ /*
+ * If we return the topmost dentry we have to make sure that it has not
+ * been moved away while we gave up the topmost parents i_mutex lock.
+ */
+ if (topmost.dentry == old->dentry) {
+ spin_lock(&old->dentry->d_lock);
+ if (oldnd->path.dentry != old->dentry->d_parent) {
+ spin_unlock(&old->dentry->d_lock);
+ dput(old->dentry);
+ name->hash = full_name_hash(name->name, name->len);
+ err = lookup_hash(oldnd, name, old);
+ if (err)
+ return err;
+ /* FIXME: What if we find a directory here ... */
+ return err;
+ }
+ spin_unlock(&old->dentry->d_lock);
+ } else
+ dput(topmost.dentry);
+
+ return 0;
+
+err_lock:
+ path_to_nameidata(&parent, oldnd);
+ path_put_conditional(old, oldnd);
+ *trap = lock_rename(oldnd->path.dentry, newnd->path.dentry);
+ return err;
+}
+
static int __lookup_one_len(const char *name, struct qstr *this,
struct dentry *base, int len)
{
@@ -3544,6 +3777,91 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
return error;
}

+static int vfs_rename_union(struct nameidata *oldnd, struct path *old,
+ struct nameidata *newnd, struct path *new)
+{
+ struct inode *old_dir = oldnd->path.dentry->d_inode;
+ struct inode *new_dir = newnd->path.dentry->d_inode;
+ struct qstr old_name;
+ char *name;
+ struct dentry *dentry;
+ int error;
+
+ if (old->dentry->d_inode == new->dentry->d_inode)
+ return 0;
+ error = may_whiteout(old_dir, old->dentry, 0);
+ if (error)
+ return error;
+ if (!old_dir->i_op || !old_dir->i_op->whiteout)
+ return -EPERM;
+
+ if (!new->dentry->d_inode)
+ error = may_create(new_dir, new->dentry);
+ else
+ error = may_delete(new_dir, new->dentry, 0);
+ if (error)
+ return error;
+
+ vfs_dq_init(old_dir);
+ vfs_dq_init(new_dir);
+
+ error = -EBUSY;
+ if (d_mountpoint(old->dentry) || d_mountpoint(new->dentry))
+ return error;
+
+ error = -ENOMEM;
+ name = kmalloc(old->dentry->d_name.len, GFP_KERNEL);
+ if (!name)
+ return error;
+ strncpy(name, old->dentry->d_name.name, old->dentry->d_name.len);
+ name[old->dentry->d_name.len] = 0;
+ old_name.len = old->dentry->d_name.len;
+ old_name.hash = old->dentry->d_name.hash;
+ old_name.name = name;
+
+ /* possibly delete the existing new file */
+ if ((newnd->path.dentry == new->dentry->d_parent) &&
+ new->dentry->d_inode) {
+ /* FIXME: inode may be truncated while we hold a lock */
+ error = vfs_unlink(new_dir, new->dentry);
+ if (error)
+ goto freename;
+
+ dentry = __lookup_hash(&new->dentry->d_name,
+ newnd->path.dentry, newnd);
+ if (IS_ERR(dentry))
+ goto freename;
+
+ dput(new->dentry);
+ new->dentry = dentry;
+ }
+
+ /* copyup to the new file */
+ error = __union_copyup(old, newnd, new);
+ if (error)
+ goto freename;
+
+ /* whiteout the old file */
+ dentry = __lookup_hash(&old_name, oldnd->path.dentry, oldnd);
+ error = PTR_ERR(dentry);
+ if (IS_ERR(dentry))
+ goto freename;
+ error = vfs_whiteout(old_dir, dentry, 0);
+ dput(dentry);
+
+ /* FIXME: This is acutally unlink() && create() ... */
+/*
+ if (!error) {
+ const char *new_name = old_dentry->d_name.name;
+ fsnotify_move(old_dir, new_dir, old_name.name, new_name, 0,
+ new_dentry->d_inode, old_dentry->d_inode);
+ }
+*/
+freename:
+ kfree(old_name.name);
+ return error;
+}
+
SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
int, newdfd, const char __user *, newname)
{
@@ -3582,7 +3900,20 @@ SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,

trap = lock_rename(new_dir, old_dir);

- error = hash_lookup_union(&oldnd, &oldnd.last, &old);
+ /*
+ * For union mounts we need to call a giant lookup_rename_source()
+ * instead.
+ * First lock_rename() and look on the topmost fs like you would do in
+ * the normal rename, if you find something which is not a directory,
+ * go ahead and lookup target and do normal rename.
+ * If you find a negative dentry, unlock_rename() and continue as
+ * _hash_lookup_union() would do without locking the topmost parent
+ * at the end. After that do lock_rename() of the source parent and the
+ * target parent and do a copyup with additional whiteout creation at
+ * the end.
+ */
+// error = hash_lookup_union(&oldnd, &oldnd.last, &old);
+ error = lookup_rename_source(&oldnd, &newnd, &trap, &oldnd.last, &old);
if (error)
goto exit3;
/* source must exist */
@@ -3601,19 +3932,21 @@ SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
error = -EINVAL;
if (old.dentry == trap)
goto exit4;
- error = hash_lookup_union(&newnd, &newnd.last, &new);
+ /* target is always on topmost fs, even with unions */
+ error = lookup_hash(&newnd, &newnd.last, &new);
if (error)
goto exit4;
/* target should not be an ancestor of source */
error = -ENOTEMPTY;
if (new.dentry == trap)
goto exit5;
- /* renaming on unions is done by the user-space */
+ /* renaming of directories on unions is done by the user-space */
error = -EXDEV;
- if (is_unionized(oldnd.path.dentry, oldnd.path.mnt))
- goto exit5;
- if (is_unionized(newnd.path.dentry, newnd.path.mnt))
+ if (is_unionized(oldnd.path.dentry, oldnd.path.mnt) &&
+ S_ISDIR(old.dentry->d_inode->i_mode))
goto exit5;
+// if (is_unionized(newnd.path.dentry, newnd.path.mnt))
+// goto exit5;

error = mnt_want_write(oldnd.path.mnt);
if (error)
@@ -3622,6 +3955,11 @@ SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
&newnd.path, new.dentry);
if (error)
goto exit6;
+ if (is_unionized(oldnd.path.dentry, oldnd.path.mnt) &&
+ (old.dentry->d_parent != oldnd.path.dentry)) {
+ error = vfs_rename_union(&oldnd, &old, &newnd, &new);
+ goto exit6;
+ }
error = vfs_rename(old_dir->d_inode, old.dentry,
new_dir->d_inode, new.dentry);
exit6:
--
1.6.3.3

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