[PATCH] tcp: do not promote SPLICE_F_NONBLOCK to socket O_NONBLOCK

[Octavian Purdila <opurdila@ixiacom.com>]

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commit 11134aa8499b6fd67569e8fd21bde6fc481898d1
Author: Octavian Purdila <opurdila@ixiacom.com>
Date:   Thu Jul 17 16:25:23 2008 +0300

    tcp: do not promote SPLICE_F_NONBLOCK to socket O_NONBLOCK
    
    This patch changes tcp_splice_read to the behavior implied by man 2
    splice:
    
         SPLICE_F_NONBLOCK - Do not block on I/O. This makes the splice
         pipe operations non-blocking, but splice() may nevertheless block
         because the file descriptors that are spliced to/from may block
         (unless they have the O_NONBLOCK flag set).
    
    This approach also provides a simple solution to the splice
    transfer size problem. Say we have the following common sequence:
    
         splice(socket, pipe);
         splice(pipe, file);
    
    Unless we specify SPLICE_F_NONBLOCK, we can't use arbitrarily large
    transfer sizes with the 1st splice since otherwise we will deadlock
    due to pipe being full.  But if we use SPLICE_F_NONBLOCK, the current
    implementation will make the underlying socket non-blocking and thus
    will force us use poll or other async I/O notification mechanism.
    
    Choosing a splice transfer size that won't deadlock is not trivial: we
    need to stay under PIPE_BUFFERS packets and since packets can have
    arbitrary sizes we will need to be conservative and use a small
    transfer size. That can degrade performance due to excessive system
    calls.
    
    Signed-off-by: Octavian Purdila <opurdila@ixiacom.com>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 56a133c..cc5082b 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -570,7 +570,7 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
 
 	lock_sock(sk);
 
-	timeo = sock_rcvtimeo(sk, flags & SPLICE_F_NONBLOCK);
+	timeo = sock_rcvtimeo(sk, sock->file->f_flags & O_NONBLOCK);
 	while (tss.len) {
 		ret = __tcp_splice_read(sk, &tss);
 		if (ret < 0)
@@ -578,10 +578,6 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
 		else if (!ret) {
 			if (spliced)
 				break;
-			if (flags & SPLICE_F_NONBLOCK) {
-				ret = -EAGAIN;
-				break;
-			}
 			if (sock_flag(sk, SOCK_DONE))
 				break;
 			if (sk->sk_err) {