netdev - [PATCH v3] net: dccp: Add SIOCOUTQ IOCTL support (send buffer fill)

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Message-Id: <20200603111051.12224-1-richard_siegfried@systemli.org>
Date:   Wed,  3 Jun 2020 13:10:51 +0200
From:   Richard Sailer <richard_siegfried@...temli.org>
To:     gerrit@....abdn.ac.uk, davem@...emloft.net, dccp@...r.kernel.org
Cc:     netdev@...r.kernel.org
Subject: [PATCH v3] net: dccp: Add SIOCOUTQ IOCTL support (send buffer fill)

This adds support for the SIOCOUTQ IOCTL to get the send buffer fill
of a DCCP socket, like UDP and TCP sockets already have.

Regarding the used data field: DCCP uses per packet sequence numbers,
not per byte, so sequence numbers can't be used like in TCP. sk_wmem_queued
is not used by DCCP and always 0, even in test on highly congested paths.
Therefore this uses sk_wmem_alloc like in UDP.

Signed-off-by: Richard Sailer <richard_siegfried@...temli.org>
---
v3: whitespace fixes
---
 Documentation/networking/dccp.txt | 2 ++
 net/dccp/proto.c                  | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/Documentation/networking/dccp.txt b/Documentation/networking/dccp.txt
index 55c575fcaf17d..682ecf8288827 100644
--- a/Documentation/networking/dccp.txt
+++ b/Documentation/networking/dccp.txt
@@ -185,6 +185,8 @@ FIONREAD
 	Works as in udp(7): returns in the `int' argument pointer the size of
 	the next pending datagram in bytes, or 0 when no datagram is pending.
 
+SIOCOUTQ
+  Returns the number of data bytes in the local send queue.
 
 Other tunables
 ==============
diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index 4af8a98fe7846..148de5ec585b2 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -375,6 +375,14 @@ int dccp_ioctl(struct sock *sk, int cmd, unsigned long arg)
 		goto out;
 
 	switch (cmd) {
+	case SIOCOUTQ: {
+		/* Using sk_wmem_alloc here because sk_wmem_queued is not used by DCCP and
+		 * always 0, comparably to UDP.
+		 */
+		int amount = sk_wmem_alloc_get(sk);
+		rc = put_user(amount, (int __user *)arg);
+	}
+		break;
 	case SIOCINQ: {
 		struct sk_buff *skb;
 		unsigned long amount = 0;
-- 
2.26.2