[PATCH] move ramfs a_ops into libfs

From Bill Irwin.

Abstract out ramfs readpage(), prepare_write(), and commit_write()
operations.

Ram-backed filesystems are going to be doing a lot of zero-filled read
and write operations.  So in this patch, ramfs' implementations are
moved to libfs in anticipation of other callers.

fs/libfs.c

@@ -277,3 +277,47 @@ int simple_rename(struct inode *old_dir, struct dentry *old_dentry, struct inode
 	}
 	return 0;
 }
+
+int simple_readpage(struct file *file, struct page *page)
+{
+	void *kaddr;
+
+	if (PageUptodate(page))
+		goto out;
+
+	kaddr = kmap_atomic(page, KM_USER0);
+	memset(kaddr, 0, PAGE_CACHE_SIZE);
+	kunmap_atomic(kaddr, KM_USER0);
+	flush_dcache_page(page);
+	SetPageUptodate(page);
+out:
+	unlock_page(page);
+	return 0;
+}
+
+int simple_prepare_write(struct file *file, struct page *page, unsigned offset, unsigned to)
+{
+	void *kaddr;
+
+	if (PageUptodate(page))
+		goto out;
+	
+	kaddr = kmap_atomic(page, KM_USER0);
+	memset(kaddr, 0, PAGE_CACHE_SIZE);
+	kunmap_atomic(kaddr, KM_USER0);
+	SetPageUptodate(page);
+out:
+	set_page_dirty(page);
+	return 0;
+}
+
+int simple_commit_write(struct file *file, struct page *page, unsigned offset, unsigned to)
+{
+	struct inode *inode = page->mapping->host;
+	loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
+
+	if (pos > inode->i_size)
+		inode->i_size = pos;
+
+	return 0;
+}

fs/ramfs/inode.c

@@ -47,48 +47,6 @@ static struct backing_dev_info ramfs_backing_dev_info = {
 	.memory_backed	= 1,	/* Does not contribute to dirty memory */
 };
 
-/*
- * Read a page. Again trivial. If it didn't already exist
- * in the page cache, it is zero-filled.
- */
-static int ramfs_readpage(struct file *file, struct page * page)
-{
-	if (!PageUptodate(page)) {
-		char *kaddr = kmap_atomic(page, KM_USER0);
-
-		memset(kaddr, 0, PAGE_CACHE_SIZE);
-		kunmap_atomic(kaddr, KM_USER0);
-		flush_dcache_page(page);
-		SetPageUptodate(page);
-	}
-	unlock_page(page);
-	return 0;
-}
-
-static int ramfs_prepare_write(struct file *file, struct page *page, unsigned offset, unsigned to)
-{
-	if (!PageUptodate(page)) {
-		char *kaddr = kmap_atomic(page, KM_USER0);
-
-		memset(kaddr, 0, PAGE_CACHE_SIZE);
-		flush_dcache_page(page);
-		kunmap_atomic(kaddr, KM_USER0);
-		SetPageUptodate(page);
-	}
-	set_page_dirty(page);
-	return 0;
-}
-
-static int ramfs_commit_write(struct file *file, struct page *page, unsigned offset, unsigned to)
-{
-	struct inode *inode = page->mapping->host;
-	loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
-
-	if (pos > inode->i_size)
-		inode->i_size = pos;
-	return 0;
-}
-
 struct inode *ramfs_get_inode(struct super_block *sb, int mode, int dev)
 {
 	struct inode * inode = new_inode(sb);
@@ -175,10 +133,10 @@ static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char *
 }
 
 static struct address_space_operations ramfs_aops = {
-	.readpage	= ramfs_readpage,
+	.readpage	= simple_readpage,
 	.writepage	= fail_writepage,
-	.prepare_write	= ramfs_prepare_write,
-	.commit_write	= ramfs_commit_write
+	.prepare_write	= simple_prepare_write,
+	.commit_write	= simple_commit_write
 };
 
 static struct file_operations ramfs_file_operations = {

include/linux/fs.h

@@ -1311,6 +1311,12 @@ extern int simple_rmdir(struct inode *, struct dentry *);
 extern int simple_rename(struct inode *, struct dentry *, struct inode *, struct dentry *);
 extern int simple_sync_file(struct file *, struct dentry *, int);
 extern int simple_empty(struct dentry *);
+extern int simple_readpage(struct file *file, struct page *page);
+extern int simple_prepare_write(struct file *file, struct page *page,
+			unsigned offset, unsigned to);
+extern int simple_commit_write(struct file *file, struct page *page,
+				unsigned offset, unsigned to);
+
 extern struct dentry *simple_lookup(struct inode *, struct dentry *);
 extern ssize_t generic_read_dir(struct file *, char *, size_t, loff_t *);
 extern struct file_operations simple_dir_operations;

kernel/ksyms.c

@@ -306,6 +306,9 @@ EXPORT_SYMBOL(simple_unlink);
 EXPORT_SYMBOL(simple_rmdir);
 EXPORT_SYMBOL(simple_rename);
 EXPORT_SYMBOL(simple_sync_file);
+EXPORT_SYMBOL(simple_readpage);
+EXPORT_SYMBOL(simple_prepare_write);
+EXPORT_SYMBOL(simple_commit_write);
 EXPORT_SYMBOL(simple_empty);
 EXPORT_SYMBOL(fd_install);
 EXPORT_SYMBOL(put_unused_fd);