From 6663f8a23e7cb60d798c5ffbd9c716b62b204f2a Mon Sep 17 00:00:00 2001
From: John Baldwin <jhb@FreeBSD.org>
Date: Tue, 25 May 2021 16:59:18 -0700
Subject: [PATCH] sglist: Add sglist_append_single_mbuf().

This function appends the contents of a single mbuf to an sglist
rather than an entire mbuf chain.

Reviewed by:	gallatin, markj
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D30135
---
 share/man/man9/Makefile |  1 +
 share/man/man9/sglist.9 | 12 +++++++++++-
 sys/kern/subr_sglist.c  | 15 +++++++++++++++
 sys/sys/sglist.h        |  1 +
 4 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/share/man/man9/Makefile b/share/man/man9/Makefile
index da68da16ddf5..4699b1ef0afe 100644
--- a/share/man/man9/Makefile
+++ b/share/man/man9/Makefile
@@ -1941,6 +1941,7 @@ MLINKS+=sglist.9 sglist_alloc.9 \
 	sglist.9 sglist_append_mbuf_epg.9 \
 	sglist.9 sglist_append_phys.9 \
 	sglist.9 sglist_append_sglist.9 \
+	sglist.9 sglist_append_single_mbuf.9 \
 	sglist.9 sglist_append_uio.9 \
 	sglist.9 sglist_append_user.9 \
 	sglist.9 sglist_append_vmpages.9 \
diff --git a/share/man/man9/sglist.9 b/share/man/man9/sglist.9
index b1d781b84d63..408d23573489 100644
--- a/share/man/man9/sglist.9
+++ b/share/man/man9/sglist.9
@@ -26,7 +26,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd April 24, 2020
+.Dd May 25, 2021
 .Dt SGLIST 9
 .Os
 .Sh NAME
@@ -38,6 +38,7 @@
 .Nm sglist_append_mbuf_epg,
 .Nm sglist_append_phys ,
 .Nm sglist_append_sglist ,
+.Nm sglist_append_single_mbuf ,
 .Nm sglist_append_uio ,
 .Nm sglist_append_user ,
 .Nm sglist_append_vmpages ,
@@ -74,6 +75,8 @@
 .Ft int
 .Fn sglist_append_sglist "struct sglist *sg" "struct sglist *source" "size_t offset" "size_t len"
 .Ft int
+.Fn sglist_append_single_mbuf "struct sglist *sg" "struct mbuf *m"
+.Ft int
 .Fn sglist_append_uio "struct sglist *sg" "struct uio *uio"
 .Ft int
 .Fn sglist_append_user "struct sglist *sg" "void *buf" "size_t len" "struct thread *td"
@@ -284,6 +287,13 @@ to the scatter/gather list
 .Fa sg .
 .Pp
 The
+.Nm sglist_append_mbuf
+function appends the physical address ranges described by a single mbuf
+.Fa m
+to the scatter/gather list
+.Fa sg .
+.Pp
+The
 .Nm sglist_append_phys
 function appends a single physical address range to the scatter/gather list
 .Fa sg .
diff --git a/sys/kern/subr_sglist.c b/sys/kern/subr_sglist.c
index 71be45b4231d..7c520fda00f5 100644
--- a/sys/kern/subr_sglist.c
+++ b/sys/kern/subr_sglist.c
@@ -466,6 +466,21 @@ sglist_append_mbuf(struct sglist *sg, struct mbuf *m0)
 	return (0);
 }
 
+/*
+ * Append the segments that describe a single mbuf to a scatter/gather
+ * list.  If there are insufficient segments, then this fails with
+ * EFBIG.
+ */
+int
+sglist_append_single_mbuf(struct sglist *sg, struct mbuf *m)
+{
+	if ((m->m_flags & M_EXTPG) != 0)
+		return (sglist_append_mbuf_epg(sg, m,
+		    mtod(m, vm_offset_t), m->m_len));
+	else
+		return (sglist_append(sg, m->m_data, m->m_len));
+}
+
 /*
  * Append the segments that describe a buffer spanning an array of VM
  * pages.  The buffer begins at an offset of 'pgoff' in the first
diff --git a/sys/sys/sglist.h b/sys/sys/sglist.h
index 82a3ac6ed6ac..bf8aa482e3ce 100644
--- a/sys/sys/sglist.h
+++ b/sys/sys/sglist.h
@@ -94,6 +94,7 @@ int	sglist_append_phys(struct sglist *sg, vm_paddr_t paddr,
 	    size_t len);
 int	sglist_append_sglist(struct sglist *sg, struct sglist *source,
 	    size_t offset, size_t length);
+int	sglist_append_single_mbuf(struct sglist *sg, struct mbuf *m);
 int	sglist_append_uio(struct sglist *sg, struct uio *uio);
 int	sglist_append_user(struct sglist *sg, void *buf, size_t len,
 	    struct thread *td);