fallocate should be a file operation

Currently all filesystems except XFS implement fallocate asynchronously,
while XFS forced a commit.  Both of these are suboptimal - in case of O_SYNC
I/O we really want our allocation on disk, especially for the !KEEP_SIZE
case where we actually grow the file with user-visible zeroes.  On the
other hand always commiting the transaction is a bad idea for fast-path
uses of fallocate like for example in recent Samba versions.   Given
that block allocation is a data plane operation anyway change it from
an inode operation to a file operation so that we have the file structure
available that lets us check for O_SYNC.

This also includes moving the code around for a few of the filesystems,
and remove the already unnedded S_ISDIR checks given that we only wire
up fallocate for regular files.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/ocfs2/file.c

@@ -1989,9 +1989,10 @@ int ocfs2_change_file_space(struct file *file, unsigned int cmd,
 	return __ocfs2_change_file_space(file, inode, file->f_pos, cmd, sr, 0);
 }
 
-static long ocfs2_fallocate(struct inode *inode, int mode, loff_t offset,
+static long ocfs2_fallocate(struct file *file, int mode, loff_t offset,
 			    loff_t len)
 {
+	struct inode *inode = file->f_path.dentry->d_inode;
 	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
 	struct ocfs2_space_resv sr;
 	int change_size = 1;
@@ -2002,9 +2003,6 @@ static long ocfs2_fallocate(struct inode *inode, int mode, loff_t offset,
 	if (!ocfs2_writes_unwritten_extents(osb))
 		return -EOPNOTSUPP;
 
-	if (S_ISDIR(inode->i_mode))
-		return -ENODEV;
-
 	if (mode & FALLOC_FL_KEEP_SIZE)
 		change_size = 0;
 
@@ -2612,7 +2610,6 @@ const struct inode_operations ocfs2_file_iops = {
 	.getxattr	= generic_getxattr,
 	.listxattr	= ocfs2_listxattr,
 	.removexattr	= generic_removexattr,
-	.fallocate	= ocfs2_fallocate,
 	.fiemap		= ocfs2_fiemap,
 };
 
@@ -2644,6 +2641,7 @@ const struct file_operations ocfs2_fops = {
 	.flock		= ocfs2_flock,
 	.splice_read	= ocfs2_file_splice_read,
 	.splice_write	= ocfs2_file_splice_write,
+	.fallocate	= ocfs2_fallocate,
 };
 
 const struct file_operations ocfs2_dops = {