Introduce the M_ZERO flag to malloc(9)

Instead of:

        foo = malloc(sizeof(foo), M_WAIT);
        bzero(foo, sizeof(foo));

You can now (and please do) use:

        foo = malloc(sizeof(foo), M_WAIT | M_ZERO);

In the future this will enable us to do idle-time pre-zeroing of
malloc-space.

share/man/man9/malloc.9

@@ -88,6 +88,8 @@ argument further qualifies
 .Fn malloc No Ns 's
 operational characteristics as follows:
 .Bl -tag -width indent
+.It Dv M_ZERO
+Causes the allocated memory to be set to all zeros.
 .It Dv M_NOWAIT
 Causes
 .Fn malloc

sys/kern/kern_malloc.c

@@ -280,6 +280,9 @@ out:
 		ksp->ks_maxused = ksp->ks_memuse;
 	splx(s);
 	mtx_exit(&malloc_mtx, MTX_DEF);
+	/* XXX: Do idle pre-zeroing.  */
+	if (va != NULL && (flags & M_ZERO))
+		bzero(va, size);
 	return ((void *) va);
 }
 

sys/sys/malloc.h

@@ -46,6 +46,7 @@
 #define	M_NOWAIT	0x0001		/* do not block */
 #define	M_USE_RESERVE	0x0002		/* can alloc out of reserve memory */
 #define	M_ASLEEP	0x0004		/* async sleep on failure */
+#define	M_ZERO		0x0008		/* bzero the allocation */
 
 #define	M_MAGIC		877983977	/* time when first defined :-) */