From: Allison Henderson <achender@linux.vnet.ibm.com>
Subject: [Ext4 punch hole 2/4 v4] Ext4 Punch Hole Support: Clear Hole
Date: Fri, 18 Mar 2011 20:03:57 -0700
Message-ID: <4D841D1D.2050005@linux.vnet.ibm.com>
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To: linux-ext4@vger.kernel.org
Sender: linux-ext4-owner@vger.kernel.org

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 3aa0b72... c722e31... M	fs/ext4/ext4.h
:100644 100644 67e7a3c... 78c5bc4... 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 3aa0b72..c722e31 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1738,6 +1738,8 @@ 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 67e7a3c..78c5bc4 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3907,9 +3907,30 @@ 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;
@@ -3922,7 +3943,15 @@ 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