Backport MHSIZE/MPKTHSIZE equivalents from head

These macros are equivalent to the ones on head, except they are only exposed
when _KERNEL is defined, i.e. to kernel code, whereas the code on head is exposed
to userland as well

This is for improved forwards compatibility with mbuf(9) macros in head@r277203+,
and is required for a clean MFC of r279393

This is a direct commit to stable/10

MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D2126
Reviewed by: glebius, rwatson
Sponsored by: EMC / Isilon Storage Division

1 files changed, 10 insertions, 0 deletions

diff --git a/sys/sys/mbuf.h b/sys/sys/mbuf.h
index 38644bf..63f7461 100644
--- a/sys/sys/mbuf.h
+++ b/sys/sys/mbuf.h
@@ -206,6 +206,16 @@ struct mbuf {
 #define	m_pktdat	M_dat.MH.MH_dat.MH_databuf
 #define	m_dat		M_dat.M_databuf
 
+/* 
+ * NOTE: forwards compatibility definitions for mbuf(9)
+ *
+ * These aren't 1:1 with the macros in r277203; in particular they're exposed
+ * to both userland and kernel, whereas this is exposed to just _KERNEL -- to
+ * avoid disruption with existing KBI/KPIs
+ */
+#define	MHSIZE		offsetof(struct mbuf, m_dat)
+#define	MPKTHSIZE	offsetof(struct mbuf, m_pktdat)
+
 /*
  * mbuf flags of global significance and layer crossing.
  * Those of only protocol/layer specific significance are to be mapped