ecryptfs: modify write path to encrypt page in writepage

Change the write path to encrypt the data only when the page is written to
disk in ecryptfs_writepage. Previously, ecryptfs encrypts the page in
ecryptfs_write_end which means that if there are multiple write requests to
the same page, ecryptfs ends up re-encrypting that page over and over again.
This patch minimizes the number of encryptions needed.

Signed-off-by: Thieu Le <thieule@chromium.org>
[tyhicks: Changed NULL .drop_inode sop pointer to generic_drop_inode]
Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
diff --git a/fs/ecryptfs/super.c b/fs/ecryptfs/super.c
index 3042fe1..bacc882 100644
--- a/fs/ecryptfs/super.c
+++ b/fs/ecryptfs/super.c
@@ -55,7 +55,6 @@
 	if (unlikely(!inode_info))
 		goto out;
 	ecryptfs_init_crypt_stat(&inode_info->crypt_stat);
-	mutex_init(&inode_info->lower_file_mutex);
 	inode_info->lower_file = NULL;
 	inode = &inode_info->vfs_inode;
 out:
@@ -198,7 +197,7 @@
 const struct super_operations ecryptfs_sops = {
 	.alloc_inode = ecryptfs_alloc_inode,
 	.destroy_inode = ecryptfs_destroy_inode,
-	.drop_inode = generic_delete_inode,
+	.drop_inode = generic_drop_inode,
 	.statfs = ecryptfs_statfs,
 	.remount_fs = NULL,
 	.evict_inode = ecryptfs_evict_inode,