net: netconsole: split send_msg_fragmented

Refactor the send_msg_fragmented() function by extracting the logic for
sending the message body into a new function called
send_fragmented_body().

Now, send_msg_fragmented() handles appending the release and header, and
then delegates the task of breaking up the body and sending the
fragments to send_fragmented_body().

This is the final flow now:

When send_ext_msg_udp() is called to send a message, it will:
  - call send_msg_no_fragmentation() if no fragmentation is needed
  or
  - call send_msg_fragmented() if fragmentation is needed
    * send_msg_fragmented() appends the header to the buffer, which is
      be persisted until the function returns
      * call send_fragmented_body() to iterate and populate the body of
	the message. It will not touch the header, and it will only
	replace the body, writing the msgbody and/or userdata.

Also add some comment to make the code easier to review.

Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/netconsole.c

@@ -1096,46 +1096,30 @@ static void append_release(char *buf)
 	scnprintf(buf, MAX_PRINT_CHUNK, "%s,", release);
 }
 
-static void send_msg_fragmented(struct netconsole_target *nt,
-				const char *msg,
-				int msg_len,
-				int release_len)
+static void send_fragmented_body(struct netconsole_target *nt, char *buf,
+				 const char *msgbody, int header_len,
+				 int msgbody_len)
 {
-	int header_len, msgbody_len, body_len;
-	static char buf[MAX_PRINT_CHUNK]; /* protected by target_list_lock */
-	int offset = 0, userdata_len = 0;
-	const char *header, *msgbody;
 	const char *userdata = NULL;
+	int body_len, offset = 0;
+	int userdata_len = 0;
 
 #ifdef CONFIG_NETCONSOLE_DYNAMIC
 	userdata = nt->userdata_complete;
 	userdata_len = nt->userdata_length;
 #endif
 
-	/* need to insert extra header fields, detect header and msgbody */
-	header = msg;
-	msgbody = memchr(msg, ';', msg_len);
-	if (WARN_ON_ONCE(!msgbody))
-		return;
-
-	header_len = msgbody - header;
-	msgbody_len = msg_len - header_len - 1;
-	msgbody++;
-
-	/*
-	 * Transfer multiple chunks with the following extra header.
-	 * "ncfrag=<byte-offset>/<total-bytes>"
+	/* body_len represents the number of bytes that will be sent. This is
+	 * bigger than MAX_PRINT_CHUNK, thus, it will be split in multiple
+	 * packets
 	 */
-	if (release_len)
-		append_release(buf);
-
-	/* Copy the header into the buffer */
-	memcpy(buf + release_len, header, header_len);
-	header_len += release_len;
-
 	body_len = msgbody_len + userdata_len;
-	/* for now on, the header will be persisted, and the msgbody
-	 * will be replaced
+
+	/* In each iteration of the while loop below, we send a packet
+	 * containing the header and a portion of the body. The body is
+	 * composed of two parts: msgbody and userdata. We keep track of how
+	 * many bytes have been sent so far using the offset variable, which
+	 * ranges from 0 to the total length of the body.
 	 */
 	while (offset < body_len) {
 		int this_header = header_len;
@@ -1144,7 +1128,7 @@ static void send_msg_fragmented(struct netconsole_target *nt,
 		int this_chunk = 0;
 
 		this_header += scnprintf(buf + this_header,
-					 sizeof(buf) - this_header,
+					 MAX_PRINT_CHUNK - this_header,
 					 ",ncfrag=%d/%d;", offset,
 					 body_len);
 
@@ -1199,6 +1183,41 @@ static void send_msg_fragmented(struct netconsole_target *nt,
 	}
 }
 
+static void send_msg_fragmented(struct netconsole_target *nt,
+				const char *msg,
+				int msg_len,
+				int release_len)
+{
+	static char buf[MAX_PRINT_CHUNK]; /* protected by target_list_lock */
+	int header_len, msgbody_len;
+	const char *msgbody;
+
+	/* need to insert extra header fields, detect header and msgbody */
+	msgbody = memchr(msg, ';', msg_len);
+	if (WARN_ON_ONCE(!msgbody))
+		return;
+
+	header_len = msgbody - msg;
+	msgbody_len = msg_len - header_len - 1;
+	msgbody++;
+
+	/*
+	 * Transfer multiple chunks with the following extra header.
+	 * "ncfrag=<byte-offset>/<total-bytes>"
+	 */
+	if (release_len)
+		append_release(buf);
+
+	/* Copy the header into the buffer */
+	memcpy(buf + release_len, msg, header_len);
+	header_len += release_len;
+
+	/* for now on, the header will be persisted, and the msgbody
+	 * will be replaced
+	 */
+	send_fragmented_body(nt, buf, msgbody, header_len, msgbody_len);
+}
+
 /**
  * send_ext_msg_udp - send extended log message to target
  * @nt: target to send message to