afs: Flush outstanding writes when an fd is closed

Flush outstanding writes in afs when an fd is closed.  This is what NFS and
CIFS do.
Reported-by: Marc Dionne <marc.c.dionne@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>

fs/afs/file.c

@@ -30,6 +30,7 @@ static int afs_readpages(struct file *filp, struct address_space *mapping,
 
 const struct file_operations afs_file_operations = {
 	.open		= afs_open,
+	.flush		= afs_flush,
 	.release	= afs_release,
 	.llseek		= generic_file_llseek,
 	.read_iter	= generic_file_read_iter,

fs/afs/internal.h

@@ -720,6 +720,7 @@ extern int afs_writepages(struct address_space *, struct writeback_control *);
 extern void afs_pages_written_back(struct afs_vnode *, struct afs_call *);
 extern ssize_t afs_file_write(struct kiocb *, struct iov_iter *);
 extern int afs_writeback_all(struct afs_vnode *);
+extern int afs_flush(struct file *, fl_owner_t);
 extern int afs_fsync(struct file *, loff_t, loff_t, int);
 
 

fs/afs/write.c

@@ -757,6 +757,20 @@ int afs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 	return ret;
 }
 
+/*
+ * Flush out all outstanding writes on a file opened for writing when it is
+ * closed.
+ */
+int afs_flush(struct file *file, fl_owner_t id)
+{
+	_enter("");
+
+	if ((file->f_mode & FMODE_WRITE) == 0)
+		return 0;
+
+	return vfs_fsync(file, 0);
+}
+
 /*
  * notification that a previously read-only page is about to become writable
  * - if it returns an error, the caller will deliver a bus error signal