pledge: define the meaning of passing NULL to one arguments of pledge(2) as "I

don't want to change the current value"

it changes only the `request' argument behaviour when NULL is passed:
previously it was traited as "" was passed.

with help from jmc@ for man-page
OK tb@ on previous version

1 files changed, 11 insertions, 2 deletions

diff --git a/lib/libc/sys/pledge.2 b/lib/libc/sys/pledge.2
index f2ea4dbb2a2..674530198fe 100644
--- a/lib/libc/sys/pledge.2
+++ b/lib/libc/sys/pledge.2
@@ -1,4 +1,4 @@
-.\" $OpenBSD: pledge.2,v 1.25 2016/02/11 16:30:35 tim Exp $
+.\" $OpenBSD: pledge.2,v 1.26 2016/03/11 05:57:16 semarie Exp $
 .\"
 .\" Copyright (c) 2015 Nicholas Marriott <nicm@openbsd.org>
 .\"
@@ -14,7 +14,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: February 11 2016 $
+.Dd $Mdocdate: March 11 2016 $
 .Dt PLEDGE 2
 .Os
 .Sh NAME
@@ -55,6 +55,14 @@ system call.
 This can be used for pure computation operating on memory shared
 with another process.
 .Pp
+Passing
+.Dv NULL
+to
+.Fa promises
+or
+.Fa paths
+specifies to not change the current value.
+.Pp
 Some system calls, when allowed, have restrictions applied to them:
 .Pp
 .Bl -tag -width "readlink(2)" -offset indent -compact
@@ -527,6 +535,7 @@ A whitelist of permitted paths may be provided in
 .Ar paths .
 All other paths will return
 .Er ENOENT .
+At least one promise is required to be pledged in order to activate whitelist.
 .Sh RETURN VALUES
 .Rv -std
 .Sh ERRORS