iflib: Make if_shared_ctx_t a pointer to const

This structure is shared among multiple instances of a driver, so we
should ensure that it doesn't somehow get treated as if there's a
separate instance per interface.  This is especially important for
software-only drivers like wg.

DEVICE_REGISTER() still returns a void * and so the per-driver sctx
structures are not yet defined with the const qualifier.

Reviewed by:	gallatin, erj
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D29102

(cherry picked from commit ffe3def903)

sys/dev/bnxt/if_bnxt.c

@@ -327,8 +327,6 @@ static struct if_shared_ctx bnxt_sctx_init = {
 	.isc_driver_version = bnxt_driver_version,
 };
 
-if_shared_ctx_t bnxt_sctx = &bnxt_sctx_init;
-
 /*
  * Device Methods
  */
@@ -336,7 +334,7 @@ if_shared_ctx_t bnxt_sctx = &bnxt_sctx_init;
 static void *
 bnxt_register(device_t dev)
 {
-	return bnxt_sctx;
+	return (&bnxt_sctx_init);
 }
 
 /*

sys/dev/e1000/if_em.c

@@ -554,8 +554,6 @@ static struct if_shared_ctx em_sctx_init = {
 	.isc_ntxd_default = {EM_DEFAULT_TXD},
 };
 
-if_shared_ctx_t em_sctx = &em_sctx_init;
-
 static struct if_shared_ctx igb_sctx_init = {
 	.isc_magic = IFLIB_MAGIC,
 	.isc_q_align = PAGE_SIZE,
@@ -583,8 +581,6 @@ static struct if_shared_ctx igb_sctx_init = {
 	.isc_ntxd_default = {EM_DEFAULT_TXD},
 };
 
-if_shared_ctx_t igb_sctx = &igb_sctx_init;
-
 /*****************************************************************
  *
  * Dump Registers
@@ -707,13 +703,13 @@ static int em_get_regs(SYSCTL_HANDLER_ARGS)
 static void *
 em_register(device_t dev)
 {
-	return (em_sctx);
+	return (&em_sctx_init);
 }
 
 static void *
 igb_register(device_t dev)
 {
-	return (igb_sctx);
+	return (&igb_sctx_init);
 }
 
 static int

sys/dev/e1000/igb_txrx.c

@@ -72,8 +72,6 @@ struct if_txrx igb_txrx = {
 	.ift_legacy_intr = em_intr
 };
 
-extern if_shared_ctx_t em_sctx;
-
 /**********************************************************************
  *
  *  Setup work for hardware segmentation offload (TSO) on

sys/dev/ixgbe/if_ix.c

@@ -392,8 +392,6 @@ static struct if_shared_ctx ixgbe_sctx_init = {
 	.isc_ntxd_default = {DEFAULT_TXD},
 };
 
-if_shared_ctx_t ixgbe_sctx = &ixgbe_sctx_init;
-
 /************************************************************************
  * ixgbe_if_tx_queues_alloc
  ************************************************************************/
@@ -855,7 +853,7 @@ ixgbe_initialize_transmit_units(if_ctx_t ctx)
 static void *
 ixgbe_register(device_t dev)
 {
-	return (ixgbe_sctx);
+	return (&ixgbe_sctx_init);
 } /* ixgbe_register */
 
 /************************************************************************

sys/dev/ixgbe/if_ixv.c

@@ -233,12 +233,10 @@ static struct if_shared_ctx ixv_sctx_init = {
 	.isc_ntxd_default = {DEFAULT_TXD},
 };
 
-if_shared_ctx_t ixv_sctx = &ixv_sctx_init;
-
 static void *
 ixv_register(device_t dev)
 {
-	return (ixv_sctx);
+	return (&ixv_sctx_init);
 }
 
 /************************************************************************

sys/dev/ixgbe/ix_txrx.c

@@ -72,8 +72,6 @@ struct if_txrx ixgbe_txrx  = {
 	.ift_legacy_intr = NULL
 };
 
-extern if_shared_ctx_t ixgbe_sctx;
-
 /************************************************************************
  * ixgbe_tx_ctx_setup
  *

sys/dev/ixl/if_iavf.c

@@ -272,13 +272,11 @@ static struct if_shared_ctx iavf_sctx_init = {
 	.isc_ntxd_default = {IXL_DEFAULT_RING},
 };
 
-if_shared_ctx_t iavf_sctx = &iavf_sctx_init;
-
 /*** Functions ***/
 static void *
 iavf_register(device_t dev)
 {
-	return (iavf_sctx);
+	return (&iavf_sctx_init);
 }
 
 static int

sys/dev/ixl/if_ixl.c

@@ -351,13 +351,11 @@ static struct if_shared_ctx ixl_sctx_init = {
 	.isc_ntxd_default = {IXL_DEFAULT_RING},
 };
 
-if_shared_ctx_t ixl_sctx = &ixl_sctx_init;
-
 /*** Functions ***/
 static void *
 ixl_register(device_t dev)
 {
-	return (ixl_sctx);
+	return (&ixl_sctx_init);
 }
 
 static int

sys/net/iflib.h

@@ -49,7 +49,7 @@ typedef uint16_t qidx_t;
 struct iflib_ctx;
 typedef struct iflib_ctx *if_ctx_t;
 struct if_shared_ctx;
-typedef struct if_shared_ctx *if_shared_ctx_t;
+typedef const struct if_shared_ctx *if_shared_ctx_t;
 struct if_int_delay_info;
 typedef struct if_int_delay_info  *if_int_delay_info_t;
 struct if_pseudo;