getcwd(3): Clarify that EACCES may or may not be checked.

POSIX permits but does not require checking access on the current and parent
directories.

Because various programs do not like it if getcwd(3) fails, it seems best
to avoid checking access as much as possible. There are various reports in
GNATS about this (search for getcwd).

Our getcwd(3) implementation first queries the kernel for the pathname
directly, which does not check any permissions but sometimes fails, and then
falls back to reading all parent directories for the names.

PR:		standards/44425
MFC after:	2 weeks

lib/libc/gen/getcwd.3

@@ -28,7 +28,7 @@
 .\"     @(#)getcwd.3	8.2 (Berkeley) 12/11/93
 .\" $FreeBSD$
 .\"
-.Dd November 24, 1997
+.Dd April 17, 2010
 .Dt GETCWD 3
 .Os
 .Sh NAME
@@ -108,8 +108,6 @@ The
 function
 will fail if:
 .Bl -tag -width Er
-.It Bq Er EACCES
-Read or search permission was denied for a component of the pathname.
 .It Bq Er EINVAL
 The
 .Fa size
@@ -124,6 +122,16 @@ The
 argument is greater than zero but smaller than the length of the pathname
 plus 1.
 .El
+.Pp
+The
+.Fn getcwd
+function
+may fail if:
+.Bl -tag -width Er
+.It Bq Er EACCES
+Read or search permission was denied for a component of the pathname.
+This is only checked in limited cases, depending on implementation details.
+.El
 .Sh SEE ALSO
 .Xr chdir 2 ,
 .Xr fchdir 2 ,