fuse: use d_materialise_unique()

Use d_materialise_unique() instead of d_splice_alias().  This allows dentry
subtrees to be moved to a new place if there moved, even if something is
referencing a dentry in the subtree (open fd, cwd, etc..).

This will also allow us to drop a subtree if it is found to be replaced by
something else.  In this case the disconnected subtree can later be
reconnected to its new location.

d_materialise_unique() ensures that a directory entry only ever has one
alias.  We keep fc->inst_mutex around the calls for d_materialise_unique()
on directories to prevent a race with mkdir "stealing" the inode.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 26 insertions, 43 deletions

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 72a5d5b04494..131d14b604ef 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -267,26 +267,6 @@ int fuse_valid_type(int m)
                 S_ISBLK(m) || S_ISFIFO(m) || S_ISSOCK(m);
 }
 
-/*
- * Add a directory inode to a dentry, ensuring that no other dentry
- * refers to this inode.  Called with fc->inst_mutex.
- */
-static struct dentry *fuse_d_add_directory(struct dentry *entry,
-                                           struct inode *inode)
-{
-        struct dentry *alias = d_find_alias(inode);
-        if (alias && !(alias->d_flags & DCACHE_DISCONNECTED)) {
-                /* This tries to shrink the subtree below alias */
-                fuse_invalidate_entry(alias);
-                dput(alias);
-                if (!hlist_empty(&inode->i_dentry))
-                        return ERR_PTR(-EBUSY);
-        } else {
-                dput(alias);
-        }
-        return d_splice_alias(inode, entry);
-}
-
 int fuse_lookup_name(struct super_block *sb, u64 nodeid, struct qstr *name,
                      struct fuse_entry_out *outarg, struct inode **inode)
 {
@@ -345,6 +325,24 @@ int fuse_lookup_name(struct super_block *sb, u64 nodeid, struct qstr *name,
         return err;
 }
 
+static struct dentry *fuse_materialise_dentry(struct dentry *dentry,
+                                              struct inode *inode)
+{
+        struct dentry *newent;
+
+        if (inode && S_ISDIR(inode->i_mode)) {
+                struct fuse_conn *fc = get_fuse_conn(inode);
+
+                mutex_lock(&fc->inst_mutex);
+                newent = d_materialise_unique(dentry, inode);
+                mutex_unlock(&fc->inst_mutex);
+        } else {
+                newent = d_materialise_unique(dentry, inode);
+        }
+
+        return newent;
+}
+
 static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
                                   unsigned int flags)
 {
@@ -352,7 +350,6 @@ static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
         struct fuse_entry_out outarg;
         struct inode *inode;
         struct dentry *newent;
-        struct fuse_conn *fc = get_fuse_conn(dir);
         bool outarg_valid = true;
 
         err = fuse_lookup_name(dir->i_sb, get_node_id(dir), &entry->d_name,
@@ -368,16 +365,10 @@ static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
         if (inode && get_node_id(inode) == FUSE_ROOT_ID)
                 goto out_iput;
 
-        if (inode && S_ISDIR(inode->i_mode)) {
-                mutex_lock(&fc->inst_mutex);
-                newent = fuse_d_add_directory(entry, inode);
-                mutex_unlock(&fc->inst_mutex);
-                err = PTR_ERR(newent);
-                if (IS_ERR(newent))
-                        goto out_iput;
-        } else {
-                newent = d_splice_alias(inode, entry);
-        }
+        newent = fuse_materialise_dentry(entry, inode);
+        err = PTR_ERR(newent);
+        if (IS_ERR(newent))
+                goto out_err;
 
         entry = newent ? newent : entry;
         if (outarg_valid)
@@ -1275,18 +1266,10 @@ static int fuse_direntplus_link(struct file *file,
         if (!inode)
                 goto out;
 
-        if (S_ISDIR(inode->i_mode)) {
-                mutex_lock(&fc->inst_mutex);
-                alias = fuse_d_add_directory(dentry, inode);
-                mutex_unlock(&fc->inst_mutex);
-                err = PTR_ERR(alias);
-                if (IS_ERR(alias)) {
-                        iput(inode);
-                        goto out;
-                }
-        } else {
-                alias = d_splice_alias(inode, dentry);
-        }
+        alias = fuse_materialise_dentry(dentry, inode);
+        err = PTR_ERR(alias);
+        if (IS_ERR(alias))
+                goto out;
 
         if (alias) {
                 dput(dentry);