Add the --unlink option to mirror

This deletes the local file before tearing down the mirror connection,
allowing us to avoid an ambiguous recovery situation.

README.txt

@@ -89,7 +89,7 @@ mirror
 ~~~~~~
 
   $ flexnbd mirror --addr <ADDR> --port <PORT> --sock SOCK 
-      [--bind <BIND-ADDR>] [global option]*
+      [--unlink] [--bind <BIND-ADDR>] [global option]*
 
 Start a migration from the server with control socket SOCK to the server
 listening at ADDR:PORT.
@@ -106,7 +106,15 @@ again.  It is not safe to resume the migration from where it left off
 because the source can't see that the backing store behind the
 destination is intact, or even on the same machine.
 
-Note: files smaller than 4096 bytes cannot be migrated.
+If the `--unlink` option is given, the local file will be deleted
+immediately before the mirror connection is terminated.  This allows
+an otherwise-ambiguous situation to be resolved: if you don't unlink
+the file and the flexnbd process at either end is terminated, it's not
+possible to tell which copy of the data is canonical.  Since the
+unlink happens as soon as the sender knows that it has transmitted all
+the data, there can be no ambiguity.
+
+Note: files smaller than 4096 bytes cannot be mirrored.
 
 Options
 ^^^^^^^
@@ -120,6 +128,10 @@ Options
 *--sock, -s SOCK*:
   The control socket of the local server to migrate from. Required.
 
+*--unlink, -u*: 
+  Unlink the served file from the local filesystem after successfully 
+  mirroring.
+
 *--bind, -b BIND-ADDR*:
   The local address to bind to. You may need this if the remote server
   is using an access control list.

src/client.c

@@ -476,7 +476,7 @@ int client_serve_request(struct client* client)
 	}
 	server_unlock_io( client->serve );
 
-	return failure;
+	return stop;
 }
 
 

src/control.c

@@ -324,22 +324,15 @@ int control_mirror(struct control_client* client, int linesc, char** lines)
 	}
 	connect_to->v4.sin_port = htobe16(raw_port);
 
+	action_at_finish = ACTION_EXIT;
 	if (linesc > 2) {
-		connect_from = xmalloc( sizeof( union mysockaddr ) );
-		if (parse_ip_to_sockaddr(&connect_from->generic, lines[2]) == 0) {
-			write_socket("1: bad bind address");
-			return -1;
-		}
-	}
-
-	if (linesc > 3) { max_Bps = atoi(lines[2]); }
-	
-	action_at_finish = ACTION_EXIT;
-	if (linesc > 4) {
-		if (strcmp("exit", lines[3]) == 0) {
+		if (strcmp("exit", lines[2]) == 0) {
 			action_at_finish = ACTION_EXIT;
 		}
-		else if (strcmp("nothing", lines[3]) == 0) {
+		else if (strcmp( "unlink", lines[2]) == 0 ) {
+			action_at_finish = ACTION_UNLINK;
+		}
+		else if (strcmp("nothing", lines[2]) == 0) {
 			action_at_finish = ACTION_NOTHING;
 		}
 		else {
@@ -348,6 +341,19 @@ int control_mirror(struct control_client* client, int linesc, char** lines)
 		}
 	}
 
+	if (linesc > 3) {
+		connect_from = xmalloc( sizeof( union mysockaddr ) );
+		if (parse_ip_to_sockaddr(&connect_from->generic, lines[2]) == 0) {
+			write_socket("1: bad bind address");
+			return -1;
+		}
+	}
+
+	if (linesc > 4) { 
+		max_Bps = atoi(lines[2]); 
+	}
+	
+	
 	if (linesc > 5) {
 		write_socket("1: unrecognised parameters to mirror");
 		return -1;

src/mirror.c

@@ -236,7 +236,7 @@ void mirror_on_exit( struct server * serve )
 
 	debug("Unlinking %s", serve->filename );
 	if ( ACTION_UNLINK == serve->mirror->action_at_finish ) {
-		server_unlink( serve->mirror );
+		server_unlink( serve );
 	}
 
 	debug("Sending disconnect");

src/mode.c

@@ -32,15 +32,25 @@ static char serve_help_text[] =
 	QUIET_LINE;
 
 
-static struct option * listen_options = serve_options;
-static char  * listen_short_options = serve_short_options;
+static struct option listen_options[] = {
+	GETOPT_HELP,
+	GETOPT_ADDR,
+	GETOPT_PORT,
+	GETOPT_FILE,
+	GETOPT_SOCK,
+	GETOPT_DENY,
+	GETOPT_QUIET,
+	GETOPT_VERBOSE,
+	{0}
+};
+static char listen_short_options[] = "hl:p:f:s:d" SOPT_QUIET SOPT_VERBOSE;
 static char listen_help_text[] =
 	"Usage: flexnbd " CMD_LISTEN " <options> [<acl_address>*]\n\n"
-	"Listen for an incoming migration on ADDR:PORT.\n\n"
+	"Listen for an incoming migration on ADDR:PORT."
 	HELP_LINE
 	"\t--" OPT_ADDR ",-l <ADDR>\tThe address to listen on.\n"
 	"\t--" OPT_PORT ",-p <PORT>\tThe port to listen on.\n"
-	"\t--" OPT_FILE ",-f <FILE>\tThe file to write to.\n"
+	"\t--" OPT_FILE ",-f <FILE>\tThe file to serve.\n"
 	"\t--" OPT_DENY ",-d\tDeny connections by default unless in ACL.\n"
 	SOCK_LINE
 	VERBOSE_LINE
@@ -107,12 +117,13 @@ static struct option mirror_options[] = {
 	GETOPT_SOCK,
 	GETOPT_ADDR,
 	GETOPT_PORT,
+	GETOPT_UNLINK,
 	GETOPT_BIND,
 	GETOPT_QUIET,
 	GETOPT_VERBOSE,
 	{0}
 };
-static char mirror_short_options[] = "hs:l:p:b:" SOPT_QUIET SOPT_VERBOSE;
+static char mirror_short_options[] = "hs:l:p:ub:" SOPT_QUIET SOPT_VERBOSE;
 static char mirror_help_text[] =
 	"Usage: flexnbd " CMD_MIRROR " <options>\n\n"
 	"Start mirroring from the server with control socket SOCK to one at ADDR:PORT.\n\n"
@@ -120,6 +131,7 @@ static char mirror_help_text[] =
 	"\t--" OPT_ADDR ",-l <ADDR>\tThe address to mirror to.\n"
 	"\t--" OPT_PORT ",-p <PORT>\tThe port to mirror to.\n"
 	SOCK_LINE
+	"\t--" OPT_UNLINK ",-u\tUnlink the local file when done.\n"
 	BIND_LINE
 	VERBOSE_LINE
 	QUIET_LINE;
@@ -316,7 +328,13 @@ void read_acl_param( int c, char **sock )
 	read_sock_param( c, sock, acl_help_text );
 }
 
-void read_mirror_param( int c, char **sock, char **ip_addr, char **ip_port, char **bind_addr )
+void read_mirror_param( 
+		int c, 
+		char **sock,
+		char **ip_addr,
+		char **ip_port,
+		int  *unlink,
+		char **bind_addr )
 {
 	switch( c ){
 		case 'h':
@@ -332,6 +350,9 @@ void read_mirror_param( int c, char **sock, char **ip_addr, char **ip_port, char
 		case 'p':
 			*ip_port = optarg;
 			break;
+		case 'u':
+			*unlink = 1;
+			break;
 		case 'b':
 			*bind_addr = optarg;
 			break;
@@ -404,15 +425,7 @@ int mode_serve( int argc, char *argv[] )
 	}
 	if ( err ) { exit_err( serve_help_text ); }
 
-	flexnbd = flexnbd_create_serving( 
-		ip_addr, 
-		ip_port, 
-		file, 
-		sock, 
-		default_deny, 
-		argc - optind, 
-		argv + optind,
-		MAX_NBD_CLIENTS );
+	flexnbd = flexnbd_create_serving( ip_addr, ip_port, file, sock, default_deny, argc - optind, argv + optind, MAX_NBD_CLIENTS );
 	flexnbd_serve( flexnbd );
 	flexnbd_destroy( flexnbd );
 
@@ -639,11 +652,19 @@ int mode_mirror( int argc, char *argv[] )
 	char *sock = NULL;
 	char *remote_argv[4] = {0};
 	int err = 0;
+	int unlink = 0;
+
+	remote_argv[2] = "exit";
 
 	while (1) {
 		c = getopt_long( argc, argv, mirror_short_options, mirror_options, NULL);
 		if ( -1 == c ) { break; }
-		read_mirror_param( c, &sock, &remote_argv[0], &remote_argv[1], &remote_argv[2] );
+		read_mirror_param( c, 
+				&sock, 
+				&remote_argv[0], 
+				&remote_argv[1], 
+				&unlink, 
+				&remote_argv[3] );
 	}
 
 	if ( NULL == sock ){
@@ -655,12 +676,13 @@ int mode_mirror( int argc, char *argv[] )
 		err = 1;
 	}
 	if ( err ) { exit_err( mirror_help_text ); }
+	if ( unlink ) { remote_argv[2] = "unlink"; }
 	
-	if (remote_argv[2] == NULL) {
-		do_remote_command( "mirror", sock, 2, remote_argv );
+	if (remote_argv[3] == NULL) {
+		do_remote_command( "mirror", sock, 3, remote_argv );
 	}
 	else {
-		do_remote_command( "mirror", sock, 3, remote_argv );
+		do_remote_command( "mirror", sock, 4, remote_argv );
 	}
 
 	return 0;

src/mode.h

@@ -21,6 +21,7 @@ void mode(char* mode, int argc, char **argv);
 #define OPT_FROM "from"
 #define OPT_SIZE "size"
 #define OPT_DENY "default-deny"
+#define OPT_UNLINK "unlink"
 
 #define CMD_SERVE  "serve"
 #define CMD_LISTEN "listen"
@@ -51,6 +52,7 @@ void mode(char* mode, int argc, char **argv);
 #define GETOPT_FROM GETOPT_ARG( OPT_FROM, 'F' )
 #define GETOPT_SIZE GETOPT_ARG( OPT_SIZE, 'S' )
 #define GETOPT_BIND GETOPT_ARG( OPT_BIND, 'b' )
+#define GETOPT_UNLINK GETOPT_ARG( OPT_UNLINK, 'u' )
 
 #define OPT_VERBOSE "verbose"
 #define SOPT_VERBOSE "v"

tests/acceptance/environment.rb

@@ -73,6 +73,10 @@ class Environment
     @nbd1.mirror_unchecked( @nbd2.ip, @nbd2.port, nil, nil, 10 )
   end
 
+  def mirror12_unlink
+    @nbd1.mirror_unlink( @nbd2.ip, @nbd2.port, 2 )
+  end
+
 
   def writefile1(data)
     @file1 = FileWriter.new(@filename1, @blocksize).write(data)

tests/acceptance/flexnbd.rb

@@ -259,14 +259,31 @@ class FlexNBD
   end
 
 
-  def mirror_cmd(dest_ip, dest_port)
-    "#{@bin} mirror "\
+  def base_mirror_opts( dest_ip, dest_port )
     "--addr #{dest_ip} "\
       "--port #{dest_port} "\
       "--sock #{ctrl} "\
+  end
+
+  def unlink_mirror_opts( dest_ip, dest_port )
+    "#{base_mirror_opts( dest_ip, dest_port )} "\
+      "--unlink "
+  end
+
+  def base_mirror_cmd( opts )
+    "#{@bin} mirror "\
+      "#{opts} "\
       "#{@debug}"
   end
 
+  def mirror_cmd(dest_ip, dest_port)
+    base_mirror_cmd( base_mirror_opts( dest_ip, dest_port ) )
+  end
+
+  def mirror_unlink_cmd( dest_ip, dest_port )
+    base_mirror_cmd( unlink_mirror_opts( dest_ip, dest_port ) )
+  end
+
   def break_cmd
     "#{@bin} break "\
       "--sock #{ctrl} "\
@@ -389,6 +406,14 @@ class FlexNBD
   end
 
 
+  def mirror_unlink( dest_ip, dest_port, timeout=nil )
+    cmd = mirror_unlink_cmd( dest_ip, dest_port )
+    debug( cmd )
+
+    maybe_timeout( cmd, timeout )
+  end
+
+
   def maybe_timeout(cmd, timeout=nil )
     stdout, stderr = "",""
     run = Proc.new do
@@ -417,6 +442,7 @@ class FlexNBD
   end
 
 
+
   def break(timeout=nil)
     cmd = break_cmd
     debug( cmd )

tests/acceptance/test_happy_path.rb

@@ -64,12 +64,17 @@ class TestHappyPath < Test::Unit::TestCase
   end
 
 
-  def test_mirror
+  def setup_to_mirror
     @env.writefile1( "f"*4 )
     @env.serve1
 
     @env.writefile2( "0"*4 )
     @env.listen2
+  end
+
+
+  def test_mirror
+    setup_to_mirror()
 
     @env.nbd1.can_die
     @env.nbd2.can_die(0)
@@ -78,11 +83,30 @@ class TestHappyPath < Test::Unit::TestCase
     @env.nbd1.join
     @env.nbd2.join
 
+    assert( File.file?( @env.filename1 ),
+           "The source file was incorrectly deleted")
     assert_equal(@env.file1.read_original( 0, @env.blocksize ),
                  @env.file2.read( 0, @env.blocksize ) )
   end
 
 
+  def test_mirror_unlink
+    setup_to_mirror()
+    assert File.file?( @env.filename1 )
+
+    stdout, stderr = @env.mirror12_unlink
+
+    assert_no_match( /unrecognized/, stderr )
+    @env.nbd1.can_die(0)
+    @env.nbd2.can_die(0)
+
+    Timeout.timeout(2) do @env.nbd1.join end
+
+    assert !File.file?( @env.filename1 )
+  end
+
+
+
   def test_write_to_high_block
     # Create a large file, then try to write to somewhere after the 2G boundary
     @env.truncate1 "4G"