linux-kernel - Do iov_len and iov_base have to be reset after EAGAIN on kernel

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Message-ID: <524f69650811031147g6c133ed8wc8031a8586d66eaa@mail.gmail.com>
Date:	Mon, 3 Nov 2008 13:47:10 -0600
From:	"Steve French" <smfrench@...il.com>
To:	"Jeff Layton" <jlayton@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Do iov_len and iov_base have to be reset after EAGAIN on kernel_recvmsg?

In cifs_demultiplex_thread Shirish suggested changing the following to
handle the case in which EAGAIN is returned from kernel_recvmsg and
has corrupted the value of iov_len and iov_base

--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -417,10 +417,16 @@ incomplete_rcv:
 			msleep(1); /* minimum sleep to prevent looping
 				allowing socket to clear and app threads to set
 				tcpStatus CifsNeedReconnect if server hung */
-			if (pdu_length < 4)
+			if (pdu_length < 4) {
+				iov.iov_base = (4 - pdu_length) +
+							(char *)smb_buffer;
+				iov.iov_len = pdu_length;
+				smb_msg.msg_control = NULL;
+				smb_msg.msg_controllen = 0;
 				goto incomplete_rcv;

based on Sridhar's comment:

"i think you are running into a case where kernel_recvmsg() is called
via 'goto incomplete_rcv'
It happens if the previous call fails with EAGAIN.  If you want to
call recvmsg() after EAGAIN failure, you need to reset iov."

It sounds strange to reset iov_len and iov_base on EAGAIN or ENOSPACE
from the socket, but seems harmless ... but what about resetting
msg_control and msg_controllen ... is that ever necessary?  Is that
safe?

-- 
Thanks,

Steve
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