[PATCH] fat: support a truncate() for expanding size (generic_cont_expand)

This patch changes generic_cont_expand(), in order to share the code
with fatfs.

  - Use vmtruncate() if ->prepare_write() returns a error.

Even if ->prepare_write() returns an error, it may already have added some
blocks.  So, this truncates blocks outside of ->i_size by vmtruncate().

  - Add generic_cont_expand_simple().

The generic_cont_expand_simple() assumes that ->prepare_write() can handle
the block boundary.  With this, we don't need to care the extra byte.

And for expanding a file size by truncate(), fatfs uses the
added generic_cont_expand_simple().

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/buffer.c

@@ -2160,11 +2160,12 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
  * truncates.  Uses prepare/commit_write to allow the filesystem to
  * deal with the hole.  
  */
-int generic_cont_expand(struct inode *inode, loff_t size)
+static int __generic_cont_expand(struct inode *inode, loff_t size,
+				 pgoff_t index, unsigned int offset)
 {
 	struct address_space *mapping = inode->i_mapping;
 	struct page *page;
-	unsigned long index, offset, limit;
+	unsigned long limit;
 	int err;
 
 	err = -EFBIG;
@@ -2176,6 +2177,37 @@ int generic_cont_expand(struct inode *inode, loff_t size)
 	if (size > inode->i_sb->s_maxbytes)
 		goto out;
 
+	err = -ENOMEM;
+	page = grab_cache_page(mapping, index);
+	if (!page)
+		goto out;
+	err = mapping->a_ops->prepare_write(NULL, page, offset, offset);
+	if (err) {
+		/*
+		 * ->prepare_write() may have instantiated a few blocks
+		 * outside i_size.  Trim these off again.
+		 */
+		unlock_page(page);
+		page_cache_release(page);
+		vmtruncate(inode, inode->i_size);
+		goto out;
+	}
+
+	err = mapping->a_ops->commit_write(NULL, page, offset, offset);
+
+	unlock_page(page);
+	page_cache_release(page);
+	if (err > 0)
+		err = 0;
+out:
+	return err;
+}
+
+int generic_cont_expand(struct inode *inode, loff_t size)
+{
+	pgoff_t index;
+	unsigned int offset;
+
 	offset = (size & (PAGE_CACHE_SIZE - 1)); /* Within page */
 
 	/* ugh.  in prepare/commit_write, if from==to==start of block, we
@@ -2183,23 +2215,22 @@ int generic_cont_expand(struct inode *inode, loff_t size)
 	** of a block
 	*/
 	if ((offset & (inode->i_sb->s_blocksize - 1)) == 0) {
+		/* caller must handle this extra byte. */
 		offset++;
 	}
 	index = size >> PAGE_CACHE_SHIFT;
-	err = -ENOMEM;
-	page = grab_cache_page(mapping, index);
-	if (!page)
-		goto out;
-	err = mapping->a_ops->prepare_write(NULL, page, offset, offset);
-	if (!err) {
-		err = mapping->a_ops->commit_write(NULL, page, offset, offset);
+
+	return __generic_cont_expand(inode, size, index, offset);
 }
-	unlock_page(page);
-	page_cache_release(page);
-	if (err > 0)
-		err = 0;
-out:
-	return err;
+
+int generic_cont_expand_simple(struct inode *inode, loff_t size)
+{
+	loff_t pos = size - 1;
+	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
+	unsigned int offset = (pos & (PAGE_CACHE_SIZE - 1)) + 1;
+
+	/* prepare/commit_write can handle even if from==to==start of block. */
+	return __generic_cont_expand(inode, size, index, offset);
 }
 
 /*
@@ -3145,6 +3176,7 @@ EXPORT_SYMBOL(fsync_bdev);
 EXPORT_SYMBOL(generic_block_bmap);
 EXPORT_SYMBOL(generic_commit_write);
 EXPORT_SYMBOL(generic_cont_expand);
+EXPORT_SYMBOL(generic_cont_expand_simple);
 EXPORT_SYMBOL(init_buffer);
 EXPORT_SYMBOL(invalidate_bdev);
 EXPORT_SYMBOL(ll_rw_block);

fs/fat/file.c

@@ -11,6 +11,7 @@
 #include <linux/msdos_fs.h>
 #include <linux/smp_lock.h>
 #include <linux/buffer_head.h>
+#include <linux/writeback.h>
 
 int fat_generic_ioctl(struct inode *inode, struct file *filp,
 		      unsigned int cmd, unsigned long arg)
@@ -124,6 +125,24 @@ struct file_operations fat_file_operations = {
 	.sendfile	= generic_file_sendfile,
 };
 
+static int fat_cont_expand(struct inode *inode, loff_t size)
+{
+	struct address_space *mapping = inode->i_mapping;
+	loff_t start = inode->i_size, count = size - inode->i_size;
+	int err;
+
+	err = generic_cont_expand_simple(inode, size);
+	if (err)
+		goto out;
+
+	inode->i_ctime = inode->i_mtime = CURRENT_TIME_SEC;
+	mark_inode_dirty(inode);
+	if (IS_SYNC(inode))
+		err = sync_page_range_nolock(inode, mapping, start, count);
+out:
+	return err;
+}
+
 int fat_notify_change(struct dentry *dentry, struct iattr *attr)
 {
 	struct msdos_sb_info *sbi = MSDOS_SB(dentry->d_sb);
@@ -132,11 +151,17 @@ int fat_notify_change(struct dentry *dentry, struct iattr *attr)
 
 	lock_kernel();
 
-	/* FAT cannot truncate to a longer file */
+	/*
+	 * Expand the file. Since inode_setattr() updates ->i_size
+	 * before calling the ->truncate(), but FAT needs to fill the
+	 * hole before it.
+	 */
 	if (attr->ia_valid & ATTR_SIZE) {
 		if (attr->ia_size > inode->i_size) {
-			error = -EPERM;
+			error = fat_cont_expand(inode, attr->ia_size);
+			if (error || attr->ia_valid == ATTR_SIZE)
 				goto out;
+			attr->ia_valid &= ~ATTR_SIZE;
 		}
 	}
 

include/linux/buffer_head.h

@@ -198,6 +198,7 @@ int block_prepare_write(struct page*, unsigned, unsigned, get_block_t*);
 int cont_prepare_write(struct page*, unsigned, unsigned, get_block_t*,
 				loff_t *);
 int generic_cont_expand(struct inode *inode, loff_t size);
+int generic_cont_expand_simple(struct inode *inode, loff_t size);
 int block_commit_write(struct page *page, unsigned from, unsigned to);
 int block_sync_page(struct page *);
 sector_t generic_block_bmap(struct address_space *, sector_t, get_block_t *);