switch a bunch of places to mnt_want_write_file()

it's both faster (in case when file has been opened for write) and cleaner.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
index ac258be..b7697d1 100644
--- a/fs/nilfs2/ioctl.c
+++ b/fs/nilfs2/ioctl.c
@@ -27,7 +27,7 @@
 #include <linux/uaccess.h>	/* copy_from_user(), copy_to_user() */
 #include <linux/vmalloc.h>
 #include <linux/compat.h>	/* compat_ptr() */
-#include <linux/mount.h>	/* mnt_want_write(), mnt_drop_write() */
+#include <linux/mount.h>	/* mnt_want_write_file(), mnt_drop_write() */
 #include <linux/buffer_head.h>
 #include <linux/nilfs2_fs.h>
 #include "nilfs.h"
@@ -119,7 +119,7 @@
 	if (get_user(flags, (int __user *)argp))
 		return -EFAULT;
 
-	ret = mnt_want_write(filp->f_path.mnt);
+	ret = mnt_want_write_file(filp);
 	if (ret)
 		return ret;
 
@@ -174,7 +174,7 @@
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	ret = mnt_want_write(filp->f_path.mnt);
+	ret = mnt_want_write_file(filp);
 	if (ret)
 		return ret;
 
@@ -210,7 +210,7 @@
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	ret = mnt_want_write(filp->f_path.mnt);
+	ret = mnt_want_write_file(filp);
 	if (ret)
 		return ret;
 
@@ -591,7 +591,7 @@
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	ret = mnt_want_write(filp->f_path.mnt);
+	ret = mnt_want_write_file(filp);
 	if (ret)
 		return ret;
 
@@ -710,7 +710,7 @@
 	if (!capable(CAP_SYS_ADMIN))
 		goto out;
 
-	ret = mnt_want_write(filp->f_path.mnt);
+	ret = mnt_want_write_file(filp);
 	if (ret)
 		goto out;