CIFS: Use multicredits for SMB 2.1/3 writes

If we negotiate SMB 2.1 and higher version of the protocol and
a server supports large write buffer size, we need to consume 1
credit per 65536 bytes. So, we need to know how many credits
we have and obtain the required number of them before constructing
a writedata structure in writepages and iovec write.

Reviewed-by: Shirish Pargaonkar <spargaonkar@suse.com>
Signed-off-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 8c53f20..54ca2b9 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -406,6 +406,9 @@
 			int);
 	/* writepages retry size */
 	unsigned int (*wp_retry_size)(struct inode *);
+	/* get mtu credits */
+	int (*wait_mtu_credits)(struct TCP_Server_Info *, unsigned int,
+				unsigned int *, unsigned int *);
 };
 
 struct smb_version_values {
@@ -642,6 +645,16 @@
 }
 
 static inline void
+add_credits_and_wake_if(struct TCP_Server_Info *server, const unsigned int add,
+			const int optype)
+{
+	if (add) {
+		server->ops->add_credits(server, add, optype);
+		wake_up(&server->request_q);
+	}
+}
+
+static inline void
 set_credits(struct TCP_Server_Info *server, const int val)
 {
 	server->ops->set_credits(server, val);
@@ -1075,6 +1088,7 @@
 	int				result;
 	unsigned int			pagesz;
 	unsigned int			tailsz;
+	unsigned int			credits;
 	unsigned int			nr_pages;
 	struct page			*pages[];
 };
@@ -1400,6 +1414,7 @@
 #define   CIFS_OBREAK_OP   0x0100    /* oplock break request */
 #define   CIFS_NEG_OP      0x0200    /* negotiate request */
 #define   CIFS_OP_MASK     0x0380    /* mask request type */
+#define   CIFS_HAS_CREDITS 0x0400    /* already has credits */
 
 /* Security Flags: indicate type of session setup needed */
 #define   CIFSSEC_MAY_SIGN	0x00001