linux-kernel - [RFC -next 04/10] splice: Add SPLICE_F

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Message-ID: <20250319001521.53249-5-jdamato@fastly.com>
Date: Wed, 19 Mar 2025 00:15:15 +0000
From: Joe Damato <jdamato@...tly.com>
To: netdev@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	asml.silence@...il.com,
	linux-fsdevel@...r.kernel.org,
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	Joe Damato <jdamato@...tly.com>
Subject: [RFC -next 04/10] splice: Add SPLICE_F_ZC and attach ubuf

Add the SPLICE_F_ZC flag and when it is set, allocate a ubuf and attach
it to generate zerocopy notifications.

Signed-off-by: Joe Damato <jdamato@...tly.com>
---
 fs/splice.c            | 20 ++++++++++++++++++++
 include/linux/splice.h |  3 ++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/fs/splice.c b/fs/splice.c
index 1f27ce6d1c34..6dc60f47f84e 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -875,6 +875,11 @@ static ssize_t splice_socket_generic(struct pipe_inode_info *pipe,
 		if (out->f_flags & O_NONBLOCK)
 			msg.msg_flags |= MSG_DONTWAIT;
 
+		if (unlikely(flags & SPLICE_F_ZC) && ubuf_info) {
+			msg.msg_flags = MSG_ZEROCOPY;
+			msg.msg_ubuf = ubuf_info;
+		}
+
 		iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, bvec, bc,
 			      len - remain);
 		ret = sock_sendmsg(sock, &msg);
@@ -1223,12 +1228,27 @@ static ssize_t do_splice_direct_actor(struct file *in, loff_t *ppos,
 	if (unlikely(out->f_flags & O_APPEND))
 		return -EINVAL;
 
+	if (unlikely(flags & SPLICE_F_ZC)) {
+		struct socket *sock = sock_from_file(out);
+		struct sock *sk = sock->sk;
+		struct ubuf_info *ubuf_info;
+
+		ubuf_info = msg_zerocopy_realloc(sk, len, NULL);
+		if (!ubuf_info)
+			return -ENOMEM;
+		sd.ubuf_info = ubuf_info;
+	}
+
 	ret = splice_direct_to_actor(in, &sd, actor);
 	if (ret > 0)
 		*ppos = sd.pos;
 
+	if (unlikely(flags & SPLICE_F_ZC))
+		refcount_dec(&sd.ubuf_info->refcnt);
+
 	return ret;
 }
+
 /**
  * do_splice_direct - splices data directly between two files
  * @in:		file to splice from
diff --git a/include/linux/splice.h b/include/linux/splice.h
index 7477df3916e2..a88588cf2754 100644
--- a/include/linux/splice.h
+++ b/include/linux/splice.h
@@ -21,8 +21,9 @@
 				 /* from/to, of course */
 #define SPLICE_F_MORE	(0x04)	/* expect more data */
 #define SPLICE_F_GIFT	(0x08)	/* pages passed in are a gift */
+#define SPLICE_F_ZC	(0x10)  /* generate zero copy notifications */
 
-#define SPLICE_F_ALL (SPLICE_F_MOVE|SPLICE_F_NONBLOCK|SPLICE_F_MORE|SPLICE_F_GIFT)
+#define SPLICE_F_ALL (SPLICE_F_MOVE|SPLICE_F_NONBLOCK|SPLICE_F_MORE|SPLICE_F_GIFT|SPLICE_F_ZC)
 
 /*
  * Passed to the actors
-- 
2.43.0