From: David Howells <dhowells@redhat.com>
Date: Thu, 4 Feb 2021 00:15:21 -0600
Subject: [PATCH] cifs: use discard iterator to discard unneeded network data
 more efficiently
Git-commit: cf0604a686b11175d8beae60281c4ccc95aaa5c2
Patch-mainline: v5.12-rc1
References: bsc#1192606

The iterator, ITER_DISCARD, that can only be used in READ mode and
just discards any data copied to it, was added to allow a network
filesystem to discard any unwanted data sent by a server.
Convert cifs_discard_from_socket() to use this.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Acked-by: Enzo Matsumiya <ematsumiya@suse.de>
---
 fs/cifs/cifsproto.h |  2 ++
 fs/cifs/cifssmb.c   |  6 +++---
 fs/cifs/connect.c   | 17 +++++++++++++++++
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h
index 32f7a013402e..75ce6f742b8d 100644
--- a/fs/cifs/cifsproto.h
+++ b/fs/cifs/cifsproto.h
@@ -232,6 +232,8 @@ extern unsigned int setup_special_user_owner_ACE(struct cifs_ace *pace);
 extern void dequeue_mid(struct mid_q_entry *mid, bool malformed);
 extern int cifs_read_from_socket(struct TCP_Server_Info *server, char *buf,
 			         unsigned int to_read);
+extern ssize_t cifs_discard_from_socket(struct TCP_Server_Info *server,
+					size_t to_read);
 extern int cifs_read_page_from_socket(struct TCP_Server_Info *server,
 					struct page *page,
 					unsigned int page_offset,
diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index 0496934feecb..c279527aae92 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -1451,9 +1451,9 @@ cifs_discard_remaining_data(struct TCP_Server_Info *server)
 	while (remaining > 0) {
 		int length;
 
-		length = cifs_read_from_socket(server, server->bigbuf,
-				min_t(unsigned int, remaining,
-				    CIFSMaxBufSize + MAX_HEADER_SIZE(server)));
+		length = cifs_discard_from_socket(server,
+				min_t(size_t, remaining,
+				      CIFSMaxBufSize + MAX_HEADER_SIZE(server)));
 		if (length < 0)
 			return length;
 		server->total_read += length;
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index b2447cea45ae..112692300fb6 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -564,6 +564,23 @@ cifs_read_from_socket(struct TCP_Server_Info *server, char *buf,
 	return cifs_readv_from_socket(server, &smb_msg);
 }
 
+ssize_t
+cifs_discard_from_socket(struct TCP_Server_Info *server, size_t to_read)
+{
+	struct msghdr smb_msg;
+
+	/*
+	 *  iov_iter_discard already sets smb_msg.type and count and iov_offset
+	 *  and cifs_readv_from_socket sets msg_control and msg_controllen
+	 *  so little to initialize in struct msghdr
+	 */
+	smb_msg.msg_name = NULL;
+	smb_msg.msg_namelen = 0;
+	iov_iter_discard(&smb_msg.msg_iter, READ, to_read);
+
+	return cifs_readv_from_socket(server, &smb_msg);
+}
+
 int
 cifs_read_page_from_socket(struct TCP_Server_Info *server, struct page *page,
 	unsigned int page_offset, unsigned int to_read)
-- 
2.33.1