ext4: enable "punch hole" functionality

This patch adds new routines: "ext4_punch_hole" "ext4_ext_punch_hole"
and "ext4_ext_check_cache"

fallocate has been modified to call ext4_punch_hole when the punch hole
flag is passed.  At the moment, we only support punching holes in
extents, so this routine is pretty much a wrapper for the ext4_ext_punch_hole
routine.

The ext4_ext_punch_hole routine first completes all outstanding writes
with the associated pages, and then releases them.  The unblock
aligned data is zeroed, and all blocks in between are punched out.

The ext4_ext_check_cache routine is very similar to ext4_ext_in_cache
except it accepts a ext4_ext_cache parameter instead of a ext4_extent
parameter.  This routine is used by ext4_ext_punch_hole to check and
see if a block in a hole that has been cached.  The ext4_ext_cache
parameter is necessary because the members ext4_extent structure are
not large enough to hold a 32 bit value.  The existing
ext4_ext_in_cache routine has become a wrapper to this new function.

[ext4 punch hole patch series 5/5 v7] 

Signed-off-by: Allison Henderson <achender@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Mingming Cao <cmm@us.ibm.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index fbe11e6..65576c0 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4419,6 +4419,31 @@ int ext4_can_truncate(struct inode *inode)
 }
 
 /*
+ * ext4_punch_hole: punches a hole in a file by releaseing the blocks
+ * associated with the given offset and length
+ *
+ * @inode:  File inode
+ * @offset: The offset where the hole will begin
+ * @len:    The length of the hole
+ *
+ * Returns: 0 on sucess or negative on failure
+ */
+
+int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
+{
+	struct inode *inode = file->f_path.dentry->d_inode;
+	if (!S_ISREG(inode->i_mode))
+		return -ENOTSUPP;
+
+	if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
+		/* TODO: Add support for non extent hole punching */
+		return -ENOTSUPP;
+	}
+
+	return ext4_ext_punch_hole(file, offset, length);
+}
+
+/*
  * ext4_truncate()
  *
  * We block out ext4_get_block() block instantiations across the entire