[PATCH v5 04/14] oxenstored: add support for systemd active sockets

["Luis R. Rodriguez" <mcgrof@do-not-panic.com>]

From: "Luis R. Rodriguez" <mcgrof@suse.com>

This adds systemd socket activation support for the Ocaml xenstored.
Ocaml lacks systemd library support so we provide our own C helpers
as is done with other functionality lacking on Ocaml.

Active sockets enables oxenstored to be loaded only if required by a system
onto which Xen is installed on. Socket activation is handled by
systemd, once a port for a service which claims a socket is used
systemd will start the required services for it, on demand. For more
details on socket activation refer to Lennart's socket-activation
post regarding this [0].

An important difference with socket activation is that systemd will set
FD_CLOEXEC for us on the socket before giving it to us, we'll sprinkly
the Unix.set_close_on_exec for LSB init next as a separate commit.

Right now this code adds a no-op for this functionality, leaving the
enablement to be done later once systemd is properly hooked into
the build system. The socket activation is ordered in aligment with
the socket activation order passed on to systemd.

[0] http://0pointer.de/blog/projects/socket-activation2.html

Cc: David Scott <dave.scott@eu.citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Vincent Hanquez <Vincent.Hanquez@eu.citrix.com>
Acked-by: Dave Scott <Dave.Scott@citrix.com>
Acked-by: Anil Madhavapeddy <anil@recoil.org>
Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>
---
 tools/ocaml/xenstored/Makefile        |  11 ++-
 tools/ocaml/xenstored/systemd.ml      |  17 +++++
 tools/ocaml/xenstored/systemd.mli     |  24 +++++++
 tools/ocaml/xenstored/systemd_stubs.c | 132 ++++++++++++++++++++++++++++++++++
 tools/ocaml/xenstored/utils.ml        |  20 ++++--
 tools/ocaml/xenstored/xenstored.ml    |   2 +
 6 files changed, 198 insertions(+), 8 deletions(-)
 create mode 100644 tools/ocaml/xenstored/systemd.ml
 create mode 100644 tools/ocaml/xenstored/systemd.mli
 create mode 100644 tools/ocaml/xenstored/systemd_stubs.c

diff --git a/tools/ocaml/xenstored/Makefile b/tools/ocaml/xenstored/Makefile
index 7fa8f53..2f55d8b 100644
--- a/tools/ocaml/xenstored/Makefile
+++ b/tools/ocaml/xenstored/Makefile
@@ -15,6 +15,14 @@ syslog_OBJS = syslog
 syslog_C_OBJS = syslog_stubs
 OCAML_LIBRARY = syslog
 
+LDFLAGS += $(LDLIBS_libxenstore)
+CFLAGS += $(CFLAGS_libxenstore)
+
+LIBS += systemd.cma systemd.cmxa
+systemd_OBJS = systemd
+systemd_C_OBJS = systemd_stubs
+OCAML_LIBRARY += systemd
+
 OBJS = define \
 	stdext \
 	trie \
@@ -36,11 +44,12 @@ OBJS = define \
 	process \
 	xenstored
 
-INTF = symbol.cmi trie.cmi syslog.cmi
+INTF = symbol.cmi trie.cmi syslog.cmi systemd.cmi
 
 XENSTOREDLIBS = \
 	unix.cmxa \
 	-ccopt -L -ccopt . syslog.cmxa \
+	-ccopt -L -ccopt . systemd.cmxa \
 	-ccopt -L -ccopt $(OCAML_TOPLEVEL)/libs/mmap $(OCAML_TOPLEVEL)/libs/mmap/xenmmap.cmxa \
 	-ccopt -L -ccopt $(OCAML_TOPLEVEL)/libs/eventchn $(OCAML_TOPLEVEL)/libs/eventchn/xeneventchn.cmxa \
 	-ccopt -L -ccopt $(OCAML_TOPLEVEL)/libs/xc $(OCAML_TOPLEVEL)/libs/xc/xenctrl.cmxa \
diff --git a/tools/ocaml/xenstored/systemd.ml b/tools/ocaml/xenstored/systemd.ml
new file mode 100644
index 0000000..2d3c8e1
--- /dev/null
+++ b/tools/ocaml/xenstored/systemd.ml
@@ -0,0 +1,17 @@
+(*
+ * Copyright (C) 2014 Luis R. Rodriguez <mcgrof@suse.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; version 2.1 only. with the special
+ * exception on linking described in file LICENSE.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *)
+
+external sd_listen_fds: string -> Unix.file_descr = "ocaml_sd_listen_fds"
+external sd_active_socket_required: unit -> bool = "ocaml_sd_active_socket_required"
+external sd_notify_ready: unit -> unit = "ocaml_sd_notify_ready"
diff --git a/tools/ocaml/xenstored/systemd.mli b/tools/ocaml/xenstored/systemd.mli
new file mode 100644
index 0000000..3a42676
--- /dev/null
+++ b/tools/ocaml/xenstored/systemd.mli
@@ -0,0 +1,24 @@
+(*
+ * Copyright (C) 2014 Luis R. Rodriguez <mcgrof@suse.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; version 2.1 only. with the special
+ * exception on linking described in file LICENSE.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *)
+
+(** Calls the C library sd_listen_fds() function for us. Although
+ *  the library doesn't accept argument we send one over to help
+ *  us do sanity checks on the expected sockets *)
+val sd_listen_fds: string -> Unix.file_descr
+
+(** Tells us whether or not systemd support was compiled in *)
+val sd_active_socket_required: unit -> bool
+
+(** Tells systemd we're ready *)
+external sd_notify_ready: unit -> unit = "ocaml_sd_notify_ready"
diff --git a/tools/ocaml/xenstored/systemd_stubs.c b/tools/ocaml/xenstored/systemd_stubs.c
new file mode 100644
index 0000000..76250df
--- /dev/null
+++ b/tools/ocaml/xenstored/systemd_stubs.c
@@ -0,0 +1,132 @@
+/*
+ * Copyright (C) 2014 Luis R. Rodriguez <mcgrof@suse.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; version 2.1 only. with the special
+ * exception on linking described in file LICENSE.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ */
+
+#include <string.h>
+#include <stdbool.h>
+#include <caml/mlvalues.h>
+#include <caml/memory.h>
+#include <caml/alloc.h>
+#include <caml/custom.h>
+#include <caml/signals.h>
+#include <caml/fail.h>
+#include <config.h>
+#include "xenstore.h"
+
+#if defined(HAVE_SYSTEMD)
+CAMLprim value ocaml_sd_listen_fds(value connect_to)
+{
+	CAMLparam1(connect_to);
+	CAMLlocal1(sock_ret);
+	int sock;
+	struct xs_sd_ctx *ctx;
+
+	sock_ret = Val_int(-1);
+	ctx = xs_get_sd_ctx();
+	if (!ctx)
+		goto out;
+
+	if (!xs_load_sd_required(ctx))
+		goto out;
+
+	sock = xs_claim_active_socket(ctx, (const char *) String_val(connect_to));
+	if (sock <= 0)
+		caml_failwith("ocaml_sd_listen_fds_init() mismatch on socket");
+
+	sock_ret = Val_int(sock);
+
+out:
+	xs_free_sd_ctx(ctx);
+	CAMLreturn(sock_ret);
+}
+
+CAMLprim value ocaml_sd_active_socket_required(value ignore)
+{
+	CAMLparam1(ignore);
+	CAMLlocal1(ret);
+	struct xs_sd_ctx *ctx;
+
+	ret = Val_false;
+
+	/* ctx can be NULL and that's OK */
+	ctx = xs_get_sd_ctx();
+	if (!ctx)
+		goto out;
+
+	if (xs_load_sd_required(ctx))
+		ret = Val_true;
+
+out:
+	xs_free_sd_ctx(ctx);
+	CAMLreturn(ret);
+}
+
+CAMLprim value ocaml_sd_notify_ready(value ignore)
+{
+	CAMLparam1(ignore);
+	CAMLlocal1(ret);
+	struct xs_sd_ctx *ctx;
+
+	ret = Val_int(-1);
+
+	ctx = xs_get_sd_ctx();
+	if (!ctx) {
+		caml_failwith("ocaml_sd_notify_ready() - failed");
+		goto out;
+	}
+
+	if (!xs_load_sd_required(ctx)) {
+		caml_failwith("ocaml_sd_notify_ready() - failed");
+		goto out;
+	}
+
+	ret = Val_int(0);
+
+	xs_sd_notify_ready(ctx);
+out:
+	xs_free_sd_ctx(ctx);
+	CAMLreturn(ret);
+}
+
+#else
+
+CAMLprim value ocaml_sd_listen_fds(value connect_to)
+{
+	CAMLparam1(connect_to);
+	CAMLlocal1(sock_ret);
+
+	sock_ret = Val_int(-1);
+
+	CAMLreturn(sock_ret);
+}
+
+CAMLprim value ocaml_sd_active_socket_required(value ignore)
+{
+	CAMLparam1(ignore);
+	CAMLlocal1(ret);
+
+	ret = Val_false;
+
+	CAMLreturn(ret);
+}
+
+CAMLprim value ocaml_sd_notify_ready(value ignore)
+{
+	CAMLparam1(ignore);
+	CAMLlocal1(ret);
+
+	ret = Val_int(-1);
+
+	CAMLreturn(ret);
+}
+#endif
diff --git a/tools/ocaml/xenstored/utils.ml b/tools/ocaml/xenstored/utils.ml
index 68b70c5..50f05c1 100644
--- a/tools/ocaml/xenstored/utils.ml
+++ b/tools/ocaml/xenstored/utils.ml
@@ -73,14 +73,20 @@ let trim_path path =
 let join_by_null ls = String.concat "\000" ls
 
 (* unix utils *)
+let create_regular_unix_socket name =
+        Unixext.unlink_safe name;
+        Unixext.mkdir_rec (Filename.dirname name) 0o700;
+        let sockaddr = Unix.ADDR_UNIX(name) in
+        let sock = Unix.socket Unix.PF_UNIX Unix.SOCK_STREAM 0 in
+        Unix.bind sock sockaddr;
+        Unix.listen sock 1;
+        sock
+
 let create_unix_socket name =
-	Unixext.unlink_safe name;
-	Unixext.mkdir_rec (Filename.dirname name) 0o700;
-	let sockaddr = Unix.ADDR_UNIX(name) in
-	let sock = Unix.socket Unix.PF_UNIX Unix.SOCK_STREAM 0 in
-	Unix.bind sock sockaddr;
-	Unix.listen sock 1;
-	sock
+        if Systemd.sd_active_socket_required() then
+                Systemd.sd_listen_fds name
+        else
+                create_regular_unix_socket name
 
 let read_file_single_integer filename =
 	let fd = Unix.openfile filename [ Unix.O_RDONLY ] 0o640 in
diff --git a/tools/ocaml/xenstored/xenstored.ml b/tools/ocaml/xenstored/xenstored.ml
index 438ecb9..b8d18c8 100644
--- a/tools/ocaml/xenstored/xenstored.ml
+++ b/tools/ocaml/xenstored/xenstored.ml
@@ -383,6 +383,8 @@ let _ =
 	while not !quit
 	do
 		try
+                        if Systemd.sd_active_socket_required() then
+                                Systemd.sd_notify_ready ();
 			main_loop ()
 		with exc ->
 			error "caught exception %s" (Printexc.to_string exc);
-- 
2.0.0.rc3.18.g00a5b79