[PATCH] Drop reliance on file->f_dentry in NFS reads/writes

Following a request by David Chow on linux fsdevel, this patch causes
NFS read and write requests to take the inode from page->mapping->host
rather than relying on file->f_dentry->d_inode. Apparently this will
simplify some work he is doing on another filesystem.

In any case, it cleans up the current mix of sometimes doing one
thing, sometimes the other (historical cruft), and puts NFS client
behaviour on par with what is done in other filesystems...

fs/nfs/read.c

@@ -452,19 +452,9 @@ nfs_readpage_result(struct rpc_task *task)
 int
 nfs_readpage(struct file *file, struct page *page)
 {
-	struct inode *inode;
+	struct inode *inode = page->mapping->host;
 	int		error;
 
-	if (!file) {
-		struct address_space *mapping = page->mapping;
-		if (!mapping)
-			BUG();
-		inode = mapping->host;
-	} else
-		inode = file->f_dentry->d_inode;
-	if (!inode)
-		BUG();
-
 	dprintk("NFS: nfs_readpage (%p %ld@%lu)\n",
 		page, PAGE_CACHE_SIZE, page->index);
 	/*

fs/nfs/write.c

@@ -239,17 +239,11 @@ nfs_writepage_async(struct file *file, struct inode *inode, struct page *page,
 int
 nfs_writepage(struct page *page)
 {
-	struct inode *inode;
+	struct inode *inode = page->mapping->host;
 	unsigned long end_index;
 	unsigned offset = PAGE_CACHE_SIZE;
 	int err;
-	struct address_space *mapping = page->mapping;
 
-	if (!mapping)
-		BUG();
-	inode = mapping->host;
-	if (!inode)
-		BUG();
 	end_index = inode->i_size >> PAGE_CACHE_SHIFT;
 
 	/* Ensure we've flushed out any previous writes */
@@ -769,7 +763,7 @@ nfs_strategy(struct inode *inode)
 int
 nfs_flush_incompatible(struct file *file, struct page *page)
 {
-	struct inode	*inode = file->f_dentry->d_inode;
+	struct inode	*inode = page->mapping->host;
 	struct nfs_page	*req;
 	int		status = 0;
 	/*
@@ -799,7 +793,7 @@ int
 nfs_updatepage(struct file *file, struct page *page, unsigned int offset, unsigned int count)
 {
 	struct dentry	*dentry = file->f_dentry;
-	struct inode	*inode = dentry->d_inode;
+	struct inode	*inode = page->mapping->host;
 	struct nfs_page	*req;
 	loff_t		end;
 	int		status = 0;