Merge branch 'splice-net-replace-sendpage-with-sendmsg-msg_splice_pages-part-1'

David Howells says:

====================
splice, net: Replace sendpage with sendmsg(MSG_SPLICE_PAGES), part 1

Here's the first tranche of patches towards providing a MSG_SPLICE_PAGES
internal sendmsg flag that is intended to replace the ->sendpage() op with
calls to sendmsg().  MSG_SPLICE_PAGES is a hint that tells the protocol
that it should splice the pages supplied if it can and copy them if not.

This will allow splice to pass multiple pages in a single call and allow
certain parts of higher protocols (e.g. sunrpc, iwarp) to pass an entire
message in one go rather than having to send them piecemeal.  This should
also make it easier to handle the splicing of multipage folios.

A helper, skb_splice_from_iter() is provided to do the work of splicing or
copying data from an iterator.  If a page is determined to be unspliceable
(such as being in the slab), then the helper will give an error.

Note that this facility is not made available to userspace and does not
provide any sort of callback.

This set consists of the following parts:

 (1) Define the MSG_SPLICE_PAGES flag and prevent sys_sendmsg() from being
     able to set it.

 (2) Add an extra argument to skb_append_pagefrags() so that something
     other than MAX_SKB_FRAGS can be used (sysctl_max_skb_frags for
     example).

 (3) Add the skb_splice_from_iter() helper to handle splicing pages into
     skbuffs for MSG_SPLICE_PAGES that can be shared by TCP, IP/UDP and
     AF_UNIX.

 (4) Implement MSG_SPLICE_PAGES support in TCP.

 (5) Make do_tcp_sendpages() just wrap sendmsg() and then fold it in to its
     various callers.

 (6) Implement MSG_SPLICE_PAGES support in IP and make udp_sendpage() just
     a wrapper around sendmsg().

 (7) Implement MSG_SPLICE_PAGES support in IP6/UDP6.

 (8) Implement MSG_SPLICE_PAGES support in AF_UNIX.

 (9) Make AF_UNIX copy unspliceable pages.

Link: https://lore.kernel.org/r/20230316152618.711970-1-dhowells@redhat.com/ # v1
Link: https://lore.kernel.org/r/20230329141354.516864-1-dhowells@redhat.com/ # v2
Link: https://lore.kernel.org/r/20230331160914.1608208-1-dhowells@redhat.com/ # v3
Link: https://lore.kernel.org/r/20230405165339.3468808-1-dhowells@redhat.com/ # v4
Link: https://lore.kernel.org/r/20230406094245.3633290-1-dhowells@redhat.com/ # v5
Link: https://lore.kernel.org/r/20230411160902.4134381-1-dhowells@redhat.com/ # v6
Link: https://lore.kernel.org/r/20230515093345.396978-1-dhowells@redhat.com/ # v7
Link: https://lore.kernel.org/r/20230518113453.1350757-1-dhowells@redhat.com/ # v8
====================

Link: https://lore.kernel.org/r/20230522121125.2595254-1-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/socket.h b/include/linux/socket.h
index 13c3a237b9c9..bd1cc3238851 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -327,6 +327,7 @@ struct ucred {
 					  */
 
 #define MSG_ZEROCOPY	0x4000000	/* Use user data in kernel path */
+#define MSG_SPLICE_PAGES 0x8000000	/* Splice the pages from the iterator in sendmsg() */
 #define MSG_FASTOPEN	0x20000000	/* Send data in TCP SYN */
 #define MSG_CMSG_CLOEXEC 0x40000000	/* Set close_on_exec for file
 					   descriptor received through
@@ -337,6 +338,8 @@ struct ucred {
 #define MSG_CMSG_COMPAT	0		/* We never have 32 bit fixups */
 #endif
 
+/* Flags to be cleared on entry by sendmsg and sendmmsg syscalls */
+#define MSG_INTERNAL_SENDMSG_FLAGS (MSG_SPLICE_PAGES)
 
 /* Setsockoptions(2) level. Thanks to BSD these must match IPPROTO_xxx */
 #define SOL_IP		0