From b864f0ef69497ac240ab82e8b99af6d66d9094f2 Mon Sep 17 00:00:00 2001
From: sephe <sephe@FreeBSD.org>
Date: Thu, 25 Aug 2016 05:35:51 +0000
Subject: [PATCH] hyperv/vmbus: Add function to calculate max # of elements in
 a bufring.

MFC after:	1 week
Sponsored by:	Microsoft
---
 sys/dev/hyperv/include/vmbus.h     |  2 ++
 sys/dev/hyperv/vmbus/vmbus_brvar.h | 12 ++++++++++++
 sys/dev/hyperv/vmbus/vmbus_chan.c  | 13 +++++++++++++
 3 files changed, 27 insertions(+)

diff --git a/sys/dev/hyperv/include/vmbus.h b/sys/dev/hyperv/include/vmbus.h
index 5843f0345e0a..452d29a92523 100644
--- a/sys/dev/hyperv/include/vmbus.h
+++ b/sys/dev/hyperv/include/vmbus.h
@@ -161,5 +161,7 @@ uint32_t	vmbus_chan_subidx(const struct vmbus_channel *chan);
 bool		vmbus_chan_is_primary(const struct vmbus_channel *chan);
 const struct hyperv_guid *
 		vmbus_chan_guid_inst(const struct vmbus_channel *chan);
+int		vmbus_chan_prplist_nelem(int br_size, int prpcnt_max,
+		    int dlen_max);
 
 #endif	/* !_VMBUS_H_ */
diff --git a/sys/dev/hyperv/vmbus/vmbus_brvar.h b/sys/dev/hyperv/vmbus/vmbus_brvar.h
index da0ca9d8f535..bd967f6e869b 100644
--- a/sys/dev/hyperv/vmbus/vmbus_brvar.h
+++ b/sys/dev/hyperv/vmbus/vmbus_brvar.h
@@ -74,6 +74,7 @@ struct sysctl_oid;
 static __inline int
 vmbus_txbr_maxpktsz(const struct vmbus_txbr *tbr)
 {
+
 	/*
 	 * - 64 bits for the trailing start index (- sizeof(uint64_t)).
 	 * - The rindex and windex can't be same (- 1).  See
@@ -82,6 +83,17 @@ vmbus_txbr_maxpktsz(const struct vmbus_txbr *tbr)
 	return (tbr->txbr_dsize - sizeof(uint64_t) - 1);
 }
 
+static __inline int
+vmbus_br_nelem(int br_size, int elem_size)
+{
+
+	/* Strip bufring header */
+	br_size -= sizeof(struct vmbus_bufring);
+	/* Add per-element trailing index */
+	elem_size += sizeof(uint64_t);
+	return (br_size / elem_size);
+}
+
 void		vmbus_br_sysctl_create(struct sysctl_ctx_list *ctx,
 		    struct sysctl_oid *br_tree, struct vmbus_br *br,
 		    const char *name);
diff --git a/sys/dev/hyperv/vmbus/vmbus_chan.c b/sys/dev/hyperv/vmbus/vmbus_chan.c
index bb88c0c7be4f..73e34f9bd34d 100644
--- a/sys/dev/hyperv/vmbus/vmbus_chan.c
+++ b/sys/dev/hyperv/vmbus/vmbus_chan.c
@@ -1411,3 +1411,16 @@ vmbus_chan_guid_inst(const struct vmbus_channel *chan)
 {
 	return &chan->ch_guid_inst;
 }
+
+int
+vmbus_chan_prplist_nelem(int br_size, int prpcnt_max, int dlen_max)
+{
+	int elem_size;
+
+	elem_size = __offsetof(struct vmbus_chanpkt_prplist,
+	    cp_range[0].gpa_page[prpcnt_max]);
+	elem_size += dlen_max;
+	elem_size = VMBUS_CHANPKT_TOTLEN(elem_size);
+
+	return (vmbus_br_nelem(br_size, elem_size));
+}