svn commit: r353167 - in head/sys/cddl/compat/opensolaris: kern sys

[Andriy Gapon]

Author: avg
Date: Mon Oct  7 07:54:34 2019
New Revision: 353167
URL: https://svnweb.freebsd.org/changeset/base/353167

Log:
  ZFS: add emulation of atomic_swap_64 and atomic_load_64
  
  Some 32-bit platforms do not provide 64-bit atomic operations that ZFS
  requires, either in userland or at all.  We emulate those operations for
  those platforms using a mutex.  That is not entirely correct and it's
  very efficient.  Besides, the loads are plain loads, so torn values are
  possible.
  
  Nevertheless, the emulation seems to work for some definition of work.
  
  This change adds atomic_swap_64, which is already used in ZFS code, and
  atomic_load_64 that can be used to prevent torn reads.
  
  MFC after:	1 week

Modified:
  head/sys/cddl/compat/opensolaris/kern/opensolaris_atomic.c
  head/sys/cddl/compat/opensolaris/sys/atomic.h

Modified: head/sys/cddl/compat/opensolaris/kern/opensolaris_atomic.c
==============================================================================
--- head/sys/cddl/compat/opensolaris/kern/opensolaris_atomic.c	Mon Oct  7 07:42:26 2019	(r353166)
+++ head/sys/cddl/compat/opensolaris/kern/opensolaris_atomic.c	Mon Oct  7 07:54:34 2019	(r353167)
@@ -71,6 +71,29 @@ atomic_dec_64(volatile uint64_t *target)
 	*target -= 1;
 	mtx_unlock(&atomic_mtx);
 }
+
+uint64_t
+atomic_swap_64(volatile uint64_t *a, uint64_t value)
+{
+	uint64_t ret;
+
+	mtx_lock(&atomic_mtx);
+	ret = *a;
+	*a = value;
+	mtx_unlock(&atomic_mtx);
+	return (ret);
+}
+
+uint64_t
+atomic_load_64(volatile uint64_t *a)
+{
+	uint64_t ret;
+
+	mtx_lock(&atomic_mtx);
+	ret = *a;
+	mtx_unlock(&atomic_mtx);
+	return (ret);
+}
 #endif
 
 uint64_t

Modified: head/sys/cddl/compat/opensolaris/sys/atomic.h
==============================================================================
--- head/sys/cddl/compat/opensolaris/sys/atomic.h	Mon Oct  7 07:42:26 2019	(r353166)
+++ head/sys/cddl/compat/opensolaris/sys/atomic.h	Mon Oct  7 07:54:34 2019	(r353167)
@@ -44,6 +44,8 @@
     !defined(ARM_HAVE_ATOMIC64) && !defined(I386_HAVE_ATOMIC64)
 extern void atomic_add_64(volatile uint64_t *target, int64_t delta);
 extern void atomic_dec_64(volatile uint64_t *target);
+extern uint64_t atomic_swap_64(volatile uint64_t *a, uint64_t value);
+extern uint64_t atomic_load_64(volatile uint64_t *a);
 #endif
 #ifndef __sparc64__
 extern uint32_t atomic_cas_32(volatile uint32_t *target, uint32_t cmp,