[PATCH manpages 2/2] udp.7: add UDP_GRO

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

From: Willem de Bruijn <willemb@google.com>

UDP_GRO was added in commit e20cf8d3f1f7
("udp: implement GRO for plain UDP sockets.")

    $ git describe --contains e20cf8d3f1f7
    linux/v5.0-rc1~129^2~379^2~8

Kernel source has example code in tools/testing/selftests/net/udpgro*

Per https://www.kernel.org/doc/man-pages/patches.html,
"Describe how you obtained the information in your patch":
I reviewed the relevant UDP_GRO patches.

Signed-off-by: Willem de Bruijn <willemb@google.com>
---
 man7/udp.7 | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/man7/udp.7 b/man7/udp.7
index ec16306df605..b4cc06791e47 100644
--- a/man7/udp.7
+++ b/man7/udp.7
@@ -229,6 +229,18 @@ calls by passing it as a
 .BR cmsg(7).
 A value of zero disables the feature.
 This option should not be used in code intended to be portable.
+.TP
+.BR UDP_GRO " (since Linux 5.0)"
+Enables UDP receive offload.
+If enabled, the socket may receive multiple datagrams worth of data as
+a single large buffer, together with a
+.BR cmsg(7)
+that holds the segment size.
+This option is the inverse of segmentation offload.
+It reduces receive cost by handling multiple datagrams worth of data
+as a single large packet in the kernel receive path, even when that
+exceeds MTU.
+This option should not be used in code intended to be portable.
 .SS Ioctls
 These ioctls can be accessed using
 .BR ioctl (2).
-- 
2.39.2.722.g9855ee24e9-goog