libsys: various updates

- move system calls for use by services from libminlib into libsys;
- move srv_fork(2) and srv_kill(2) from RS and into libsys;
- replace getprocnr(2) with sef_self(3);
- rename previous getnprocnr(2) to getprocnr(2);
- clean up getepinfo(2);
- change all libsys calls that used _syscall to use _taskcall, so as
  to avoid going through errno to pass errors; this is already how
  most calls work anyway, and many of the calls previously using
  _syscall were already assumed to return the actual error;
- initialize request messages to zero, for future compatibility
  (note that this does not include PCI calls, which are in need of a
  much bigger overhaul, nor kernel calls);
- clean up more of dead DS code as a side effect.

Change-Id: I8788f54c68598fcf58e23486e270c2d749780ebb

lib/libsys/getepinfo.c

@@ -0,0 +1,75 @@
+#include "syslib.h"
+#include <string.h>
+#include <unistd.h>
+
+#include <sys/ucred.h>
+
+static pid_t
+getepinfo(endpoint_t proc_ep, uid_t *uid, gid_t *gid)
+{
+	message m;
+	int r;
+
+	memset(&m, 0, sizeof(m));
+	m.PM_GETEPINFO_ENDPT = proc_ep;
+
+	if ((r = _taskcall(PM_PROC_NR, GETEPINFO, &m)) < 0)
+		return r;
+
+	if (uid != NULL)
+		*uid = m.PM_GETEPINFO_UID;
+	if (gid != NULL)
+		*gid = m.PM_GETEPINFO_GID;
+	return (pid_t) r;
+}
+
+pid_t
+getnpid(endpoint_t proc_ep)
+{
+	return getepinfo(proc_ep, NULL, NULL);
+}
+
+uid_t
+getnuid(endpoint_t proc_ep)
+{
+	uid_t uid;
+	int r;
+
+	if ((r = getepinfo(proc_ep, &uid, NULL)) < 0)
+		return (uid_t) r;
+
+	return uid;
+}
+
+gid_t
+getngid(endpoint_t proc_ep)
+{
+	gid_t gid;
+	int r;
+
+	if ((r = getepinfo(proc_ep, NULL, &gid)) < 0)
+		return (gid_t) r;
+
+	return gid;
+}
+
+int
+getnucred(endpoint_t proc_ep, struct uucred *ucred)
+{
+	uid_t uid;
+	gid_t gid;
+	int r;
+
+	if (ucred == NULL)
+		return EFAULT;
+
+	if ((r = getepinfo(proc_ep, &uid, &gid)) < 0)
+		return r;
+
+	/* Only two fields are used for now; ensure the rest is zeroed out. */
+	memset(ucred, 0, sizeof(struct uucred));
+	ucred->cr_uid = uid;
+	ucred->cr_gid = gid;
+
+	return r;
+}