3 files changed, 32 insertions, 2 deletions

diff --git a/sys/sys/fcntl.h b/sys/sys/fcntl.h
index d5b29e656f23..6bbf156ebe60 100644
--- a/sys/sys/fcntl.h
+++ b/sys/sys/fcntl.h
@@ -106,12 +106,12 @@
 /* bits to save after open */
 #define	FMASK		(FREAD|FWRITE|FAPPEND|FASYNC|FFSYNC|FNONBLOCK)
 /* bits settable by fcntl(F_SETFL, ...) */
-#define	FCNTLFLAGS	(FAPPEND|FASYNC|FFSYNC|FNONBLOCK)
+#define	FCNTLFLAGS	(FAPPEND|FASYNC|FFSYNC|FNONBLOCK|FPOSIXSHM)
 #endif
 
 /*
  * The O_* flags used to have only F* names, which were used in the kernel
- * and by fcntl.  We retain the F* names for the kernel f_flags field
+ * and by fcntl.  We retain the F* names for the kernel f_flag field
  * and for backward compatibility for fcntl.
  */
 #ifndef _POSIX_SOURCE
@@ -124,6 +124,22 @@
 #endif
 
 /*
+ * We are out of bits in f_flag (which is a short).  However,
+ * the flag bits not set in FMASK are only meaningful in the
+ * initial open syscall.  Those bits can thus be given a
+ * different meaning for fcntl(2).
+ */
+#ifndef _POSIX_SOURCE
+
+/*
+ * Set by shm_open(3) to get automatic MAP_ASYNC behavior
+ * for POSIX shared memory objects (which are otherwise
+ * implemented as plain files).
+ */
+#define	FPOSIXSHM	O_NOFOLLOW
+#endif
+
+/*
  * Constants used for fcntl(2)
  */
 
diff --git a/sys/sys/unistd.h b/sys/sys/unistd.h
index 11e74f623feb..515c69f14090 100644
--- a/sys/sys/unistd.h
+++ b/sys/sys/unistd.h
@@ -160,6 +160,10 @@
 #define _POSIX_MEMLOCK_RANGE
 #endif
 
+/* ??? #define	_POSIX_FSYNC			1 */
+#define	_POSIX_MAPPED_FILES		1
+#define _POSIX_SHARED_MEMORY_OBJECTS	1
+
 /* POSIX.1B sysconf options */
 #define _SC_ASYNCHRONOUS_IO	28
 #define _SC_MAPPED_FILES	29
diff --git a/sys/vm/vm_mmap.c b/sys/vm/vm_mmap.c
index 53462f4bccf4..d617d0c2d3ba 100644
--- a/sys/vm/vm_mmap.c
+++ b/sys/vm/vm_mmap.c
@@ -282,6 +282,16 @@ mmap(p, uap)
 			return (EBADF);
 		if (fp->f_type != DTYPE_VNODE)
 			return (EINVAL);
+		/*
+		 * POSIX shared-memory objects are defined to have
+		 * kernel persistence, and are not defined to support
+		 * read(2)/write(2) -- or even open(2).  Thus, we can
+		 * use MAP_ASYNC to trade on-disk coherence for speed.
+		 * The shm_open(3) library routine turns on the FPOSIXSHM
+		 * flag to request this behavior.
+		 */
+		if (fp->f_flag & FPOSIXSHM)
+			flags |= MAP_NOSYNC;
 		vp = (struct vnode *) fp->f_data;
 		if (vp->v_type != VREG && vp->v_type != VCHR)
 			return (EINVAL);