[PATCH 3 of 4 V6] libxl: refactor migrate_domain and generalize migrate_receive

[Shriram Rajagopalan <rshriram@cs.ubc.ca>]

# HG changeset patch
# User Shriram Rajagopalan <rshriram@cs.ubc.ca>
# Date 1337283422 25200
# Node ID b633a458bf3a931ad610363a8ce55b2970f7da65
# Parent  d5d5d596044526b59f6a3e6fd81f6171c90efe6e
libxl: refactor migrate_domain and generalize migrate_receive

Refactor some tasks like establishing the migration channel,
initial migration protocol exchange into separate functions,
to facilitate re-use, when remus support is introduced. Also,
make migrate_receive generic (instead of resorting to stdin and
stdout as the file descriptors for communication).

Signed-off-by: Shriram Rajagopalan <rshriram@cs.ubc.ca>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

diff -r d5d5d5960445 -r b633a458bf3a tools/libxl/xl_cmdimpl.c
--- a/tools/libxl/xl_cmdimpl.c	Thu May 17 12:37:00 2012 -0700
+++ b/tools/libxl/xl_cmdimpl.c	Thu May 17 12:37:02 2012 -0700
@@ -2670,6 +2670,42 @@
     exit(0);
 }
 
+static pid_t create_migration_child(const char *rune, int *send_fd,
+                                        int *recv_fd)
+{
+    int sendpipe[2], recvpipe[2];
+    pid_t child = -1;
+
+    if (!rune || !send_fd || !recv_fd)
+        return -1;
+
+    MUST( libxl_pipe(ctx, sendpipe) );
+    MUST( libxl_pipe(ctx, recvpipe) );
+
+    child = xl_fork(ctx);
+
+    if (!child) {
+        dup2(sendpipe[0], 0);
+        dup2(recvpipe[1], 1);
+        close(sendpipe[0]); close(sendpipe[1]);
+        close(recvpipe[0]); close(recvpipe[1]);
+        execlp("sh","sh","-c",rune,(char*)0);
+        perror("failed to exec sh");
+        exit(-1);
+    }
+
+    close(sendpipe[0]);
+    close(recvpipe[1]);
+    *send_fd = sendpipe[1];
+    *recv_fd = recvpipe[0];
+
+    /* if receiver dies, we get an error and can clean up
+       rather than just dying */
+    signal(SIGPIPE, SIG_IGN);
+
+    return child;
+}
+
 static int migrate_read_fixedmessage(int fd, const void *msg, int msgsz,
                                      const char *what, const char *rune) {
     char buf[msgsz];
@@ -2755,52 +2791,17 @@
     migration_child = 0;
 }
 
-static void migrate_domain(const char *domain_spec, const char *rune,
-                           const char *override_config_file)
+static void migrate_do_preamble(int send_fd, int recv_fd, pid_t child,
+                                uint8_t *config_data, int config_len,
+                                const char *rune)
 {
-    pid_t child = -1;
-    int rc;
-    int sendpipe[2], recvpipe[2];
-    int send_fd, recv_fd;
-    libxl_domain_suspend_info suspinfo;
-    char *away_domname;
-    char rc_buf;
-    uint8_t *config_data;
-    int config_len;
-
-    save_domain_core_begin(domain_spec, override_config_file,
-                           &config_data, &config_len);
-
-    if (!config_len) {
-        fprintf(stderr, "No config file stored for running domain and "
-                "none supplied - cannot migrate.\n");
+    int rc = 0;
+
+    if (send_fd < 0 || recv_fd < 0) {
+        fprintf(stderr, "migrate_do_preamble: invalid file descriptors\n");
         exit(1);
     }
 
-    MUST( libxl_pipe(ctx, sendpipe) );
-    MUST( libxl_pipe(ctx, recvpipe) );
-
-    child = xl_fork(ctx);
-
-    if (!child) {
-        dup2(sendpipe[0], 0);
-        dup2(recvpipe[1], 1);
-        close(sendpipe[0]); close(sendpipe[1]);
-        close(recvpipe[0]); close(recvpipe[1]);
-        execlp("sh","sh","-c",rune,(char*)0);
-        perror("failed to exec sh");
-        exit(-1);
-    }
-
-    close(sendpipe[0]);
-    close(recvpipe[1]);
-    send_fd = sendpipe[1];
-    recv_fd = recvpipe[0];
-
-    signal(SIGPIPE, SIG_IGN);
-    /* if receiver dies, we get an error and can clean up
-       rather than just dying */
-
     rc = migrate_read_fixedmessage(recv_fd, migrate_receiver_banner,
                                    sizeof(migrate_receiver_banner)-1,
                                    "banner", rune);
@@ -2813,6 +2814,34 @@
     save_domain_core_writeconfig(send_fd, "migration stream",
                                  config_data, config_len);
 
+}
+
+static void migrate_domain(const char *domain_spec, const char *rune,
+                           const char *override_config_file)
+{
+    pid_t child = -1;
+    int rc;
+    int send_fd = -1, recv_fd = -1;
+    libxl_domain_suspend_info suspinfo;
+    char *away_domname;
+    char rc_buf;
+    uint8_t *config_data;
+    int config_len;
+
+    save_domain_core_begin(domain_spec, override_config_file,
+                           &config_data, &config_len);
+
+    if (!config_len) {
+        fprintf(stderr, "No config file stored for running domain and "
+                "none supplied - cannot migrate.\n");
+        exit(1);
+    }
+
+    child = create_migration_child(rune, &send_fd, &recv_fd);
+
+    migrate_do_preamble(send_fd, recv_fd, child, config_data, config_len,
+                        rune);
+
     xtl_stdiostream_adjust_flags(logger, XTL_STDIOSTREAM_HIDE_PROGRESS, 0);
 
     memset(&suspinfo, 0, sizeof(suspinfo));
@@ -2936,7 +2965,8 @@
     if (rc) { fprintf(stderr,"core dump failed (rc=%d)\n",rc);exit(-1); }
 }
 
-static void migrate_receive(int debug, int daemonize, int monitor)
+static void migrate_receive(int debug, int daemonize, int monitor,
+                            int send_fd, int recv_fd)
 {
     int rc, rc2;
     char rc_buf;
@@ -2948,7 +2978,7 @@
 
     fprintf(stderr, "migration target: Ready to receive domain.\n");
 
-    CHK_ERRNO( libxl_write_exactly(ctx, 1,
+    CHK_ERRNO( libxl_write_exactly(ctx, send_fd,
                                    migrate_receiver_banner,
                                    sizeof(migrate_receiver_banner)-1,
                                    "migration ack stream",
@@ -2960,7 +2990,7 @@
     dom_info.monitor = monitor;
     dom_info.paused = 1;
     dom_info.restore_file = "incoming migration stream";
-    dom_info.migrate_fd = 0; /* stdin */
+    dom_info.migrate_fd = recv_fd;
     dom_info.migration_domname_r = &migration_domname;
     dom_info.incr_generationid = 0;
 
@@ -2974,13 +3004,13 @@
     fprintf(stderr, "migration target: Transfer complete,"
             " requesting permission to start domain.\n");
 
-    rc = libxl_write_exactly(ctx, 1,
+    rc = libxl_write_exactly(ctx, send_fd,
                              migrate_receiver_ready,
                              sizeof(migrate_receiver_ready),
                              "migration ack stream", "ready message");
     if (rc) exit(-rc);
 
-    rc = migrate_read_fixedmessage(0, migrate_permission_to_go,
+    rc = migrate_read_fixedmessage(recv_fd, migrate_permission_to_go,
                                    sizeof(migrate_permission_to_go),
                                    "GO message", 0);
     if (rc) goto perhaps_destroy_notify_rc;
@@ -2999,7 +3029,7 @@
     rc = 0;
 
  perhaps_destroy_notify_rc:
-    rc2 = libxl_write_exactly(ctx, 1,
+    rc2 = libxl_write_exactly(ctx, send_fd,
                               migrate_report, sizeof(migrate_report),
                               "migration ack stream",
                               "success/failure report");
@@ -3007,7 +3037,7 @@
 
     rc_buf = -rc;
     assert(!!rc_buf == !!rc);
-    rc2 = libxl_write_exactly(ctx, 1, &rc_buf, 1,
+    rc2 = libxl_write_exactly(ctx, send_fd, &rc_buf, 1,
                               "migration ack stream",
                               "success/failure code");
     if (rc2) exit(-ERROR_BADFAIL);
@@ -3025,7 +3055,7 @@
         fprintf(stderr, "migration target: Cleanup OK, granting sender"
                 " permission to resume.\n");
 
-        rc2 = libxl_write_exactly(ctx, 1,
+        rc2 = libxl_write_exactly(ctx, send_fd,
                                   migrate_permission_to_go,
                                   sizeof(migrate_permission_to_go),
                                   "migration ack stream",
@@ -3122,7 +3152,9 @@
         help("migrate-receive");
         return 2;
     }
-    migrate_receive(debug, daemonize, monitor);
+    migrate_receive(debug, daemonize, monitor,
+                    STDOUT_FILENO, STDIN_FILENO);
+
     return 0;
 }