From: Allison Henderson <achender@linux.vnet.ibm.com>
Subject: [Ext4 punch hole 2/5 v6] Ext4 Punch Hole Support: Clear Hole
Date: Tue, 03 May 2011 09:55:20 -0700
Message-ID: <4DC03378.1020102@linux.vnet.ibm.com>
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To: Ext4 Developers List <linux-ext4@vger.kernel.org>
Sender: linux-ext4-owner@vger.kernel.org

Sorry, I lost the subject header on this one.  
It's the same patch, but I'll resend to avoid confusion

This patch adds routines needed to zero out the
unblock aligned data of the hole.

The existing ext4_block_truncate_page routine that
is used to zero out unblock aligned data from truncate
has been modified to accept a length parameter, and
renamed to ext4_block_zero_page_range.

The function can now be used to zero out the
head of a block, the tail of a block, or the middle
of a block.  The existing ext4_block_truncate_page
has now become a wrapper to this function

Signed-off-by: Allison Henderson <achender@us.ibm.com>
---
:100644 100644 5639fdf... 45136d8... M	fs/ext4/ext4.h
:100644 100644 a04128f... dc45631... M	fs/ext4/inode.c
 fs/ext4/ext4.h  |    2 ++
 fs/ext4/inode.c |   33 +++++++++++++++++++++++++++++++--
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 5639fdf..45136d8 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1743,6 +1743,8 @@ extern int ext4_writepage_trans_blocks(struct inode *);
 extern int ext4_chunk_trans_blocks(struct inode *, int nrblocks);
 extern int ext4_block_truncate_page(handle_t *handle,
 		struct address_space *mapping, loff_t from);
+extern int ext4_block_zero_page_range(handle_t *handle,
+		struct address_space *mapping, loff_t from, loff_t length);
 extern int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf);
 extern qsize_t *ext4_get_reserved_space(struct inode *inode);
 extern void ext4_da_update_reserve_space(struct inode *inode,
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index a04128f..dc45631 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3915,9 +3915,30 @@ void ext4_set_aops(struct inode *inode)
 int ext4_block_truncate_page(handle_t *handle,
 		struct address_space *mapping, loff_t from)
 {
+	unsigned offset = from & (PAGE_CACHE_SIZE-1);
+	unsigned length;
+	unsigned blocksize;
+	struct inode *inode = mapping->host;
+
+	blocksize = inode->i_sb->s_blocksize;
+	length = blocksize - (offset & (blocksize - 1));
+
+	return ext4_block_zero_page_range(handle, mapping, from, length);
+}
+
+/*
+ * ext4_block_zero_page_range() zeros out a mapping of length 'length'
+ * starting from file offset 'from'.  The range to be zero'd must
+ * be contained with in one block.  If the specified range exceeds
+ * the end of the block it will be shortened to end of the block
+ * that cooresponds to 'from'
+ */
+int ext4_block_zero_page_range(handle_t *handle,
+		struct address_space *mapping, loff_t from, loff_t length)
+{
 	ext4_fsblk_t index = from >> PAGE_CACHE_SHIFT;
 	unsigned offset = from & (PAGE_CACHE_SIZE-1);
-	unsigned blocksize, length, pos;
+	unsigned blocksize, max, pos;
 	ext4_lblk_t iblock;
 	struct inode *inode = mapping->host;
 	struct buffer_head *bh;
@@ -3930,7 +3951,15 @@ int ext4_block_truncate_page(handle_t *handle,
 		return -EINVAL;
 
 	blocksize = inode->i_sb->s_blocksize;
-	length = blocksize - (offset & (blocksize - 1));
+	max = blocksize - (offset & (blocksize - 1));
+
+	/*
+	 * correct length if it does not fall between
+	 * 'from' and the end of the block
+	 */
+	if (length > max || length < 0)
+		length = max;
+
 	iblock = index << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);
 
 	if (!page_has_buffers(page))
-- 
1.7.1