rename the generic fsync implementations

We don't name our generic fsync implementations very well currently.
The no-op implementation for in-memory filesystems currently is called
simple_sync_file which doesn't make too much sense to start with,
the the generic one for simple filesystems is called simple_fsync
which can lead to some confusion.

This patch renames the generic file fsync method to generic_file_fsync
to match the other generic_file_* routines it is supposed to be used
with, and the no-op implementation to noop_fsync to make it obvious
what to expect.  In addition add some documentation for both methods.

Signed-off-by: Christoph Hellwig <[email protected]>
Signed-off-by: Al Viro <[email protected]>

fs/sysv/dir.c

@@ -24,7 +24,7 @@ const struct file_operations sysv_dir_operations = {
 	.llseek		= generic_file_llseek,
 	.read		= generic_read_dir,
 	.readdir	= sysv_readdir,
-	.fsync		= simple_fsync,
+	.fsync		= generic_file_fsync,
 };
 
 static inline void dir_put_page(struct page *page)

fs/sysv/file.c

@@ -26,7 +26,7 @@ const struct file_operations sysv_file_operations = {
 	.write		= do_sync_write,
 	.aio_write	= generic_file_aio_write,
 	.mmap		= generic_file_mmap,
-	.fsync		= simple_fsync,
+	.fsync		= generic_file_fsync,
 	.splice_read	= generic_file_splice_read,
 };