fs/9p: Expand setup of writeback cache to all levels

If cache is enabled, make sure we are putting the right things
in place (mainly impacts mmap).  This also sets us up for more
cache levels.
Signed-off-by: Eric Van Hensbergen <ericvh@kernel.org>
Reviewed-by: Dominique Martinet <asmadeus@codewreck.org>

fs/9p/v9fs.c

@@ -468,7 +468,7 @@ struct p9_fid *v9fs_session_init(struct v9fs_session_info *v9ses,
 
 #ifdef CONFIG_9P_FSCACHE
 	/* register the session for caching */
-	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) {
+	if (v9ses->cache == CACHE_FSCACHE) {
 		rc = v9fs_cache_session_get_cookie(v9ses, dev_name);
 		if (rc < 0)
 			goto err_clnt;

fs/9p/vfs_addr.c

@@ -279,8 +279,6 @@ static int v9fs_write_begin(struct file *filp, struct address_space *mapping,
 
 	p9_debug(P9_DEBUG_VFS, "filp %p, mapping %p\n", filp, mapping);
 
-	BUG_ON(!v9inode->writeback_fid);
-
 	/* Prefetch area to be written into the cache if we're caching this
 	 * file.  We need to do this before we get a lock on the page in case
 	 * there's more than one writer competing for the same cache block.

fs/9p/vfs_file.c

@@ -73,8 +73,7 @@ int v9fs_file_open(struct inode *inode, struct file *file)
 	}
 
 	mutex_lock(&v9inode->v_mutex);
-	if ((v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) &&
-	    !v9inode->writeback_fid &&
+	if ((v9ses->cache) && !v9inode->writeback_fid &&
 	    ((file->f_flags & O_ACCMODE) != O_RDONLY)) {
 		/*
 		 * clone a fid and add it to writeback_fid
@@ -92,9 +91,11 @@ int v9fs_file_open(struct inode *inode, struct file *file)
 		v9inode->writeback_fid = (void *) writeback_fid;
 	}
 	mutex_unlock(&v9inode->v_mutex);
-	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
+#ifdef CONFIG_9P_FSCACHE
+	if (v9ses->cache == CACHE_FSCACHE)
 		fscache_use_cookie(v9fs_inode_cookie(v9inode),
 				   file->f_mode & FMODE_WRITE);
+#endif
 	v9fs_open_fid_add(inode, &fid);
 	return 0;
 out_error:

fs/9p/vfs_inode.c

@@ -843,8 +843,7 @@ v9fs_vfs_atomic_open(struct inode *dir, struct dentry *dentry,
 	inode = d_inode(dentry);
 	v9inode = V9FS_I(inode);
 	mutex_lock(&v9inode->v_mutex);
-	if ((v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) &&
-	    !v9inode->writeback_fid &&
+	if ((v9ses->cache) && !v9inode->writeback_fid &&
 	    ((flags & O_ACCMODE) != O_RDONLY)) {
 		/*
 		 * clone a fid and add it to writeback_fid

fs/9p/vfs_inode_dotl.c

@@ -316,8 +316,7 @@ v9fs_vfs_atomic_open_dotl(struct inode *dir, struct dentry *dentry,
 
 	v9inode = V9FS_I(inode);
 	mutex_lock(&v9inode->v_mutex);
-	if ((v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) &&
-	    !v9inode->writeback_fid &&
+	if ((v9ses->cache) && !v9inode->writeback_fid &&
 	    ((flags & O_ACCMODE) != O_RDONLY)) {
 		/*
 		 * clone a fid and add it to writeback_fid
@@ -340,9 +339,11 @@ v9fs_vfs_atomic_open_dotl(struct inode *dir, struct dentry *dentry,
 	if (err)
 		goto out;
 	file->private_data = ofid;
-	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
+#ifdef CONFIG_9P_FSCACHE
+	if (v9ses->cache == CACHE_FSCACHE)
 		fscache_use_cookie(v9fs_inode_cookie(v9inode),
 				   file->f_mode & FMODE_WRITE);
+#endif
 	v9fs_open_fid_add(inode, &ofid);
 	file->f_mode |= FMODE_CREATED;
 out: