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[Libguestfs] [PATCH libnbd 2/2] api: Implement local command with systemd socket activation.



This adds new APIs for running a local NBD server and connecting to it
using systemd socket activation (instead of stdin/stdout).

This includes interop tests against nbdkit and qemu-nbd which I
believe are the only NBD servers supporting socket activation.  (If we
find others then we can add more interop tests in future.)

The upstream spec for systemd socket activation is here:
http://0pointer.de/blog/projects/socket-activation.html
---
 .gitignore                  |   2 +
 TODO                        |   2 -
 generator/generator         |  53 +++++++++++++++++-
 generator/states-connect.c  | 109 ++++++++++++++++++++++++++++++++++++
 interop/Makefile.am         |  22 ++++++++
 interop/socket-activation.c |  92 ++++++++++++++++++++++++++++++
 lib/connect.c               |  28 +++++++++
 lib/handle.c                |  10 ++++
 lib/internal.h              |   6 ++
 9 files changed, 319 insertions(+), 5 deletions(-)

diff --git a/.gitignore b/.gitignore
index dd8a052..99fce5c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -71,6 +71,8 @@ Makefile.in
 /interop/interop-qemu-nbd
 /interop/interop-qemu-nbd-tls-certs
 /interop/interop-qemu-nbd-tls-psk
+/interop/socket-activation-nbdkit
+/interop/socket-activation-qemu-nbd
 /interop/structured-read
 /lib/api.c
 /lib/libnbd.pc
diff --git a/TODO b/TODO
index 642d39f..92e2c47 100644
--- a/TODO
+++ b/TODO
@@ -17,8 +17,6 @@ NBD_INFO_BLOCK_SIZE.
 
 TLS should properly shut down the session (calling gnutls_bye).
 
-Implement nbd_connect + systemd socket activation.
-
 Improve function trace output so that:
  - Long strings are truncated.
  - Strings with non-printable characters are escaped.
diff --git a/generator/generator b/generator/generator
index 3b63665..d0b4d46 100755
--- a/generator/generator
+++ b/generator/generator
@@ -95,6 +95,7 @@ type external_event =
   | CmdConnectUnix              (* [nbd_aio_connect_unix] *)
   | CmdConnectTCP               (* [nbd_aio_connect_tcp] *)
   | CmdConnectCommand           (* [nbd_aio_connect_command] *)
+  | CmdConnectSA                (* [nbd_aio_connect_socket_activation] *)
   | CmdIssue                    (* issuing an NBD command *)
 
 type location = string * int    (* source location: file, line number *)
@@ -168,13 +169,15 @@ let rec state_machine = [
                         CmdConnectSockAddr, "CONNECT.START";
                         CmdConnectUnix, "CONNECT_UNIX.START";
                         CmdConnectTCP, "CONNECT_TCP.START";
-                        CmdConnectCommand, "CONNECT_COMMAND.START" ];
+                        CmdConnectCommand, "CONNECT_COMMAND.START";
+                        CmdConnectSA, "CONNECT_SA.START" ];
   };
 
   Group ("CONNECT", connect_state_machine);
   Group ("CONNECT_UNIX", connect_unix_state_machine);
   Group ("CONNECT_TCP", connect_tcp_state_machine);
   Group ("CONNECT_COMMAND", connect_command_state_machine);
+  Group ("CONNECT_SA", connect_sa_state_machine);
 
   Group ("MAGIC", magic_state_machine);
   Group ("OLDSTYLE", oldstyle_state_machine);
@@ -272,6 +275,16 @@ and connect_command_state_machine = [
   };
 ]
 
+(* State machine implementing [nbd_aio_connect_socket_activation]. *)
+and connect_sa_state_machine = [
+  State {
+    default_state with
+    name = "START";
+    comment = "Connect to a subprocess with systemd socket activation";
+    external_events = [];
+  };
+]
+
 (* Parse initial magic string from the server. *)
 and magic_state_machine = [
   State {
@@ -1501,6 +1514,18 @@ behave like inetd clients, such as C<nbdkit --single>.";
     example = Some "examples/connect-command.c";
   };
 
+  "connect_socket_activation", {
+    default_call with
+    args = [ StringList "argv" ]; ret = RErr;
+    permitted_states = [ Created ];
+    shortdesc = "connect using systemd socket activation";
+    longdesc = "\
+Run the command as a subprocess and connect to it using
+systemd socket activation.  This is for use with NBD servers
+such as C<nbdkit> which understand socket activation.";
+    see_also = ["L<nbd_kill_subprocess(3)>"];
+  };
+
   "is_read_only", {
     default_call with
     args = []; ret = RBool;
@@ -2093,6 +2118,22 @@ Run the command as a subprocess and begin connecting to it over
 stdin/stdout.  Parameters behave as documented in
 L<nbd_connect_command(3)>.
 
+You can check if the connection is still connecting by calling
+L<nbd_aio_is_connecting(3)>, or if it has connected to the server
+and completed the NBD handshake by calling L<nbd_aio_is_ready(3)>,
+on the connection.";
+  };
+
+  "aio_connect_socket_activation", {
+    default_call with
+    args = [ StringList "argv" ]; ret = RErr;
+    permitted_states = [ Created ];
+    shortdesc = "connect using systemd socket activation";
+    longdesc = "\
+Run the command as a subprocess and begin connecting to it using
+systemd socket activation.  Parameters behave as documented in
+L<nbd_connect_socket_activation(3)>.
+
 You can check if the connection is still connecting by calling
 L<nbd_aio_is_connecting(3)>, or if it has connected to the server
 and completed the NBD handshake by calling L<nbd_aio_is_ready(3)>,
@@ -2678,6 +2719,8 @@ let first_version = [
   "get_protocol", (1, 2);
   "set_handshake_flags", (1, 2);
   "get_handshake_flags", (1, 2);
+  "connect_socket_activation", (1, 2);
+  "aio_connect_socket_activation", (1, 2);
 
   (* These calls are proposed for a future version of libnbd, but
    * have not been added to any released version so far.
@@ -3035,7 +3078,8 @@ end = struct
 let all_external_events =
   [NotifyRead; NotifyWrite;
    CmdCreate;
-   CmdConnectSockAddr; CmdConnectUnix; CmdConnectTCP; CmdConnectCommand;
+   CmdConnectSockAddr; CmdConnectUnix; CmdConnectTCP;
+   CmdConnectCommand; CmdConnectSA;
    CmdIssue]
 
 let string_of_external_event = function
@@ -3046,6 +3090,7 @@ let string_of_external_event = function
   | CmdConnectUnix -> "CmdConnectUnix"
   | CmdConnectTCP -> "CmdConnectTCP"
   | CmdConnectCommand -> "CmdConnectCommand"
+  | CmdConnectSA -> "CmdConnectSA"
   | CmdIssue -> "CmdIssue"
 
 let c_string_of_external_event = function
@@ -3056,6 +3101,7 @@ let c_string_of_external_event = function
   | CmdConnectUnix -> "cmd_connect_unix"
   | CmdConnectTCP -> "cmd_connect_tcp"
   | CmdConnectCommand -> "cmd_connect_command"
+  | CmdConnectSA -> "cmd_connect_sa"
   | CmdIssue -> "cmd_issue"
 
 (* Find a state in the state machine hierarchy by path.  The [path]
@@ -3484,7 +3530,8 @@ let generate_lib_states_c () =
           | NotifyWrite -> pr "    r |= LIBNBD_AIO_DIRECTION_WRITE;\n"
           | CmdCreate
           | CmdConnectSockAddr
-          | CmdConnectUnix | CmdConnectTCP | CmdConnectCommand
+          | CmdConnectUnix | CmdConnectTCP
+          | CmdConnectCommand | CmdConnectSA
           | CmdIssue -> ()
       ) events;
       pr "    break;\n";
diff --git a/generator/states-connect.c b/generator/states-connect.c
index e9b3582..51b907e 100644
--- a/generator/states-connect.c
+++ b/generator/states-connect.c
@@ -37,6 +37,9 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 
+/* This is baked into the systemd socket activation API. */
+#define FIRST_SOCKET_ACTIVATION_FD 3
+
 /* Disable Nagle's algorithm on the socket, but don't fail. */
 static void
 disable_nagle (int sock)
@@ -292,4 +295,110 @@ disable_nagle (int sock)
   SET_NEXT_STATE (%^MAGIC.START);
   return 0;
 
+ CONNECT_SA.START:
+  /* This is in some ways similar to nbd_aio_connect_command above,
+   * but we must pass a listening socket to the child process and
+   * we must set LISTEN_PID and LISTEN_FDS environment variables.
+   */
+  size_t len;
+  int s;
+  struct sockaddr_un addr;
+  pid_t pid;
+  int flags;
+  char listen_pid[16];
+
+  assert (!h->sock);
+  assert (h->argv);
+  assert (h->argv[0]);
+
+  /* Use /tmp instead of TMPDIR because we must ensure the path is
+   * short enough to store in the sockaddr_un.  On some platforms this
+   * may cause problems so we may need to revisit it.  XXX
+   */
+  h->sa_tmpdir = strdup ("/tmp/libnbdXXXXXX");
+  h->sa_sockpath = strdup ("/tmp/libnbdXXXXXX/sock");
+  if (h->sa_tmpdir == NULL || h->sa_sockpath == NULL) {
+    SET_NEXT_STATE (%.DEAD);
+    set_error (errno, "strdup");
+    return 0;
+  }
+
+  if (mkdtemp (h->sa_tmpdir) == NULL) {
+    SET_NEXT_STATE (%.DEAD);
+    set_error (errno, "mkdtemp");
+    return 0;
+  }
+  len = strlen (h->sa_tmpdir);
+  memcpy (h->sa_sockpath, h->sa_tmpdir, len);
+
+  s = socket (AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
+  if (s == -1) {
+    SET_NEXT_STATE (%.DEAD);
+    set_error (errno, "socket");
+    return 0;
+  }
+
+  addr.sun_family = AF_UNIX;
+  memcpy (addr.sun_path, h->sa_sockpath, strlen (h->sa_sockpath) + 1);
+  if (bind (s, (struct sockaddr *) &addr, sizeof addr) == -1) {
+    SET_NEXT_STATE (%.DEAD);
+    set_error (errno, "bind: %s", h->sa_sockpath);
+    return 0;
+  }
+
+  if (listen (s, 1) == -1) {
+    SET_NEXT_STATE (%.DEAD);
+    set_error (errno, "listen");
+    return 0;
+  }
+
+  pid = fork ();
+  if (pid == -1) {
+    SET_NEXT_STATE (%.DEAD);
+    set_error (errno, "fork");
+    close (s);
+    return 0;
+  }
+  if (pid == 0) {         /* child - run command */
+    if (s != FIRST_SOCKET_ACTIVATION_FD) {
+      dup2 (s, FIRST_SOCKET_ACTIVATION_FD);
+      close (s);
+    }
+    else {
+      /* We must unset CLOEXEC on the fd.  (dup2 above does this
+       * implicitly because CLOEXEC is set on the fd, not on the
+       * socket).
+       */
+      flags = fcntl (s, F_GETFD, 0);
+      if (flags == -1) {
+        perror ("fcntl: F_GETFD");
+        _exit (EXIT_FAILURE);
+      }
+      if (fcntl (s, F_SETFD, flags & ~FD_CLOEXEC) == -1) {
+        perror ("fcntl: F_SETFD");
+        _exit (EXIT_FAILURE);
+      }
+    }
+
+    snprintf (listen_pid, sizeof listen_pid, "%ld", (long) getpid ());
+    setenv ("LISTEN_PID", listen_pid, 1);
+    setenv ("LISTEN_FDS", "1", 1);
+
+    /* Restore SIGPIPE back to SIG_DFL. */
+    signal (SIGPIPE, SIG_DFL);
+
+    execvp (h->argv[0], h->argv);
+    perror (h->argv[0]);
+    _exit (EXIT_FAILURE);
+  }
+
+  /* Parent. */
+  close (s);
+  h->pid = pid;
+
+  h->connaddrlen = sizeof addr;
+  memcpy (&h->connaddr, &addr, h->connaddrlen);
+  SET_NEXT_STATE (%^CONNECT.START);
+  return 0;
+
 } /* END STATE MACHINE */
diff --git a/interop/Makefile.am b/interop/Makefile.am
index 43350a8..d30cdf1 100644
--- a/interop/Makefile.am
+++ b/interop/Makefile.am
@@ -48,11 +48,13 @@ if HAVE_QEMU_NBD
 check_PROGRAMS += \
 	interop-qemu-nbd \
 	dirty-bitmap \
+	socket-activation-qemu-nbd \
 	structured-read \
 	$(NULL)
 TESTS += \
 	interop-qemu-nbd \
 	dirty-bitmap.sh \
+	socket-activation-qemu-nbd \
 	structured-read.sh \
 	$(NULL)
 
@@ -124,6 +126,15 @@ dirty_bitmap_CPPFLAGS = -I$(top_srcdir)/include
 dirty_bitmap_CFLAGS = $(WARNINGS_CFLAGS)
 dirty_bitmap_LDADD = $(top_builddir)/lib/libnbd.la
 
+socket_activation_qemu_nbd_SOURCES = socket-activation.c
+socket_activation_qemu_nbd_CPPFLAGS = \
+	-I$(top_srcdir)/include \
+	-DSERVER=\"$(QEMU_NBD)\" \
+	-DSERVER_PARAMS='"-f", "raw", "-x", "", tmpfile' \
+	$(NULL)
+socket_activation_qemu_nbd_CFLAGS = $(WARNINGS_CFLAGS)
+socket_activation_qemu_nbd_LDADD = $(top_builddir)/lib/libnbd.la
+
 structured_read_SOURCES = structured-read.c
 structured_read_CPPFLAGS = -I$(top_srcdir)/include
 structured_read_CFLAGS = $(WARNINGS_CFLAGS)
@@ -135,9 +146,11 @@ if HAVE_NBDKIT
 
 check_PROGRAMS += \
 	interop-nbdkit \
+	socket-activation-nbdkit \
 	$(NULL)
 TESTS += \
 	interop-nbdkit \
+	socket-activation-nbdkit \
 	$(NULL)
 
 # See above comment about files in ../tests/Makefile.am
@@ -245,6 +258,15 @@ interop_nbdkit_tls_psk_allow_fallback_CPPFLAGS = \
 interop_nbdkit_tls_psk_allow_fallback_CFLAGS = $(WARNINGS_CFLAGS)
 interop_nbdkit_tls_psk_allow_fallback_LDADD = $(top_builddir)/lib/libnbd.la
 
+socket_activation_nbdkit_SOURCES = socket-activation.c
+socket_activation_nbdkit_CPPFLAGS = \
+	-I$(top_srcdir)/include \
+	-DSERVER=\"$(NBDKIT)\" \
+	-DSERVER_PARAMS='"file", tmpfile' \
+	$(NULL)
+socket_activation_nbdkit_CFLAGS = $(WARNINGS_CFLAGS)
+socket_activation_nbdkit_LDADD = $(top_builddir)/lib/libnbd.la
+
 endif HAVE_NBDKIT
 
 check-valgrind:
diff --git a/interop/socket-activation.c b/interop/socket-activation.c
new file mode 100644
index 0000000..db6f6ca
--- /dev/null
+++ b/interop/socket-activation.c
@@ -0,0 +1,92 @@
+/* NBD client library in userspace
+ * Copyright (C) 2019 Red Hat Inc.
+ *
+ * This library 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; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library 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.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/* Test interop with nbdkit or qemu-nbd, and systemd socket activation. */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <inttypes.h>
+#include <unistd.h>
+
+#include <libnbd.h>
+
+#define SIZE 1048576
+
+int
+main (int argc, char *argv[])
+{
+  struct nbd_handle *nbd;
+  char tmpfile[] = "/tmp/nbdXXXXXX";
+  int fd;
+  int64_t actual_size;
+  char buf[512];
+  int r = -1;
+
+  /* Create a large sparse temporary file. */
+  fd = mkstemp (tmpfile);
+  if (fd == -1 ||
+      ftruncate (fd, SIZE) == -1 ||
+      close (fd) == -1) {
+    perror (tmpfile);
+    goto out;
+  }
+
+  nbd = nbd_create ();
+  if (nbd == NULL) {
+    fprintf (stderr, "%s\n", nbd_get_error ());
+    goto out;
+  }
+
+  char *args[] = { SERVER, SERVER_PARAMS, NULL };
+  if (nbd_connect_socket_activation (nbd, args) == -1) {
+    fprintf (stderr, "%s\n", nbd_get_error ());
+    goto out;
+  }
+
+  actual_size = nbd_get_size (nbd);
+  if (actual_size == -1) {
+    fprintf (stderr, "%s\n", nbd_get_error ());
+    goto out;
+  }
+  if (actual_size != SIZE) {
+    fprintf (stderr, "%s: actual size %" PRIi64 " <> expected size %d",
+             argv[0], actual_size, SIZE);
+    goto out;
+  }
+
+  if (nbd_pread (nbd, buf, sizeof buf, 0, 0) == -1) {
+    fprintf (stderr, "%s\n", nbd_get_error ());
+    goto out;
+  }
+
+  if (nbd_shutdown (nbd, 0) == -1) {
+    fprintf (stderr, "%s\n", nbd_get_error ());
+    goto out;
+  }
+
+  nbd_close (nbd);
+
+  r = 0;
+ out:
+  unlink (tmpfile);
+
+  exit (r == 0 ? EXIT_SUCCESS : EXIT_FAILURE);
+}
diff --git a/lib/connect.c b/lib/connect.c
index f98bcdb..c1cbef7 100644
--- a/lib/connect.c
+++ b/lib/connect.c
@@ -112,6 +112,16 @@ nbd_unlocked_connect_command (struct nbd_handle *h, char **argv)
   return wait_until_connected (h);
 }
 
+/* Connect to a local command, use systemd socket activation. */
+int
+nbd_unlocked_connect_socket_activation (struct nbd_handle *h, char **argv)
+{
+  if (nbd_unlocked_aio_connect_socket_activation (h, argv) == -1)
+    return -1;
+
+  return wait_until_connected (h);
+}
+
 int
 nbd_unlocked_aio_connect (struct nbd_handle *h,
                           const struct sockaddr *addr, socklen_t len)
@@ -405,3 +415,21 @@ nbd_unlocked_aio_connect_command (struct nbd_handle *h, char **argv)
 
   return nbd_internal_run (h, cmd_connect_command);
 }
+
+int
+nbd_unlocked_aio_connect_socket_activation (struct nbd_handle *h, char **argv)
+{
+  char **copy;
+
+  copy = nbd_internal_copy_string_list (argv);
+  if (!copy) {
+    set_error (errno, "copy_string_list");
+    return -1;
+  }
+
+  if (h->argv)
+    nbd_internal_free_string_list (h->argv);
+  h->argv = copy;
+
+  return nbd_internal_run (h, cmd_connect_sa);
+}
diff --git a/lib/handle.c b/lib/handle.c
index 5ad818e..18cc8d0 100644
--- a/lib/handle.c
+++ b/lib/handle.c
@@ -129,6 +129,16 @@ nbd_close (struct nbd_handle *h)
   free_cmd_list (h->cmds_in_flight);
   free_cmd_list (h->cmds_done);
   nbd_internal_free_string_list (h->argv);
+  if (h->sa_sockpath) {
+    if (h->pid > 0)
+      kill (h->pid, SIGTERM);
+    unlink (h->sa_sockpath);
+    free (h->sa_sockpath);
+  }
+  if (h->sa_tmpdir) {
+    rmdir (h->sa_tmpdir);
+    free (h->sa_tmpdir);
+  }
   free (h->unixsocket);
   free (h->hostname);
   free (h->port);
diff --git a/lib/internal.h b/lib/internal.h
index bdb0e83..bf8b9aa 100644
--- a/lib/internal.h
+++ b/lib/internal.h
@@ -188,6 +188,12 @@ struct nbd_handle {
   char **argv;
   pid_t pid;
 
+  /* When using systemd socket activation, this directory and socket
+   * must be deleted, and the pid above must be killed.
+   */
+  char *sa_tmpdir;
+  char *sa_sockpath;
+
   /* When connecting to Unix domain socket. */
   char *unixsocket;
 
-- 
2.23.0


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