Support for stackable file systems on top of nfs

The following patch allows stackable file systems, such as ClearCase's
mvfs, to run atop nfs.  mvfs has it's own file and inode structures, but
points its inode->i_mapping to the lower file system's mapping.  This
causes problems when nfs's address space operations try to extract the
open context from file->private_data.

The patch adds a small overhead of checking the file structure to see if
it contains an inode that is not the mapping's host.

I am curious if there are any other stackable file systems that could
benefit from this.

Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>

diff -Nurp linux-2.6.14-git/fs/nfs/direct.c linux/fs/nfs/direct.c
--- linux-2.6.14-git/fs/nfs/direct.c	2005-11-07 07:53:49.000000000 -0600
+++ linux/fs/nfs/direct.c	2005-11-09 14:58:59.000000000 -0600
@@ -604,7 +604,19 @@ nfs_direct_IO(int rw, struct kiocb *iocb
 	if (!is_sync_kiocb(iocb))
 		return result;
 
-	ctx = (struct nfs_open_context *)file->private_data;
+	if (nfs_is_valid_file(file))
+		ctx = get_nfs_open_context((struct nfs_open_context *)
+				file->private_data);
+	else {
+		/* file belongs to a stackable file system.
+		 * Can't trust the inode either */
+		inode = inode->i_mapping->host;
+
+		ctx = nfs_find_open_context(inode, NULL,
+				(rw == READ) ? FMODE_READ : FMODE_WRITE);
+		if (ctx == NULL)
+			return -EBADF;
+	}
 	switch (rw) {
 	case READ:
 		dprintk("NFS: direct_IO(read) (%s) off/no(%Lu/%lu)\n",
@@ -623,6 +635,7 @@ nfs_direct_IO(int rw, struct kiocb *iocb
 	default:
 		break;
 	}
+	put_nfs_open_context(ctx);
 	return result;
 }
 
diff -Nurp linux-2.6.14-git/fs/nfs/read.c linux/fs/nfs/read.c
--- linux-2.6.14-git/fs/nfs/read.c	2005-11-07 07:53:49.000000000 -0600
+++ linux/fs/nfs/read.c	2005-11-09 11:47:05.000000000 -0600
@@ -506,7 +506,7 @@ int nfs_readpage(struct file *file, stru
 	if (error)
 		goto out_error;
 
-	if (file == NULL) {
+	if (!nfs_is_valid_file(file)) {
 		ctx = nfs_find_open_context(inode, NULL, FMODE_READ);
 		if (ctx == NULL)
 			return -EBADF;
@@ -575,7 +575,7 @@ int nfs_readpages(struct file *filp, str
 			(long long)NFS_FILEID(inode),
 			nr_pages);
 
-	if (filp == NULL) {
+	if (!nfs_is_valid_file(filp)) {
 		desc.ctx = nfs_find_open_context(inode, NULL, FMODE_READ);
 		if (desc.ctx == NULL)
 			return -EBADF;
diff -Nurp linux-2.6.14-git/fs/nfs/write.c linux/fs/nfs/write.c
--- linux-2.6.14-git/fs/nfs/write.c	2005-11-07 07:53:49.000000000 -0600
+++ linux/fs/nfs/write.c	2005-11-09 14:14:33.000000000 -0600
@@ -703,10 +703,16 @@ static struct nfs_page * nfs_update_requ
 
 int nfs_flush_incompatible(struct file *file, struct page *page)
 {
-	struct nfs_open_context *ctx = (struct nfs_open_context *)file->private_data;
+	struct nfs_open_context *ctx;
 	struct inode	*inode = page->mapping->host;
 	struct nfs_page	*req;
 	int		status = 0;
+
+	if (nfs_is_valid_file(file))
+		ctx = (struct nfs_open_context *)file->private_data;
+	else
+		ctx = NULL;
+
 	/*
 	 * Look for a request corresponding to this page. If there
 	 * is one, and it belongs to another file, we flush it out
@@ -733,7 +739,7 @@ int nfs_flush_incompatible(struct file *
 int nfs_updatepage(struct file *file, struct page *page,
 		unsigned int offset, unsigned int count)
 {
-	struct nfs_open_context *ctx = (struct nfs_open_context *)file->private_data;
+	struct nfs_open_context *ctx;
 	struct inode	*inode = page->mapping->host;
 	struct nfs_page	*req;
 	int		status = 0;
@@ -743,14 +749,23 @@ int nfs_updatepage(struct file *file, st
 		file->f_dentry->d_name.name, count,
 		(long long)(page_offset(page) +offset));
 
+	if (nfs_is_valid_file(file))
+		ctx = get_nfs_open_context((struct nfs_open_context *)
+				file->private_data);
+	else {
+		ctx = nfs_find_open_context(inode, NULL, FMODE_WRITE);
+		if (!ctx)
+			return -EBADF;
+	}
+		
 	if (IS_SYNC(inode)) {
 		status = nfs_writepage_sync(ctx, inode, page, offset, count, 0);
 		if (status > 0) {
 			if (offset == 0 && status == PAGE_CACHE_SIZE)
 				SetPageUptodate(page);
-			return 0;
+			status = 0;
 		}
-		return status;
+		goto out;
 	}
 
 	/* If we're not using byte range locks, and we know the page
@@ -803,6 +818,8 @@ done:
 			status, (long long)i_size_read(inode));
 	if (status < 0)
 		ClearPageUptodate(page);
+out:
+	put_nfs_open_context(ctx);
 	return status;
 }
 
diff -Nurp linux-2.6.14-git/include/linux/nfs_fs.h linux/include/linux/nfs_fs.h
--- linux-2.6.14-git/include/linux/nfs_fs.h	2005-11-07 07:53:50.000000000 -0600
+++ linux/include/linux/nfs_fs.h	2005-11-09 11:44:53.000000000 -0600
@@ -350,6 +350,20 @@ static inline struct rpc_cred *nfs_file_
 }
 
 /*
+ * A stackable file system may have it's own file & inode structures, which
+ * point to the local inode's mapping.  The address space operations cannot
+ * use the stackable file system's file structure to get to the open context
+ */
+static inline int nfs_is_valid_file(struct file *file)
+{
+	struct inode *inode;
+	if (!file)
+		return 0;
+	inode = file->f_dentry->d_inode;
+	return (inode == inode->i_mapping->host);
+}
+
+/*
  * linux/fs/nfs/xattr.c
  */
 #ifdef CONFIG_NFS_V3_ACL

-- 
David Kleikamp
IBM Linux Technology Center

-
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html