remap: Add cmdline option to allow linked remap

By default crtools shouldn't modify the environment, except for
killing the dumped tasks. The link remap does so and should sit
under explicit cmdline option.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

crtools.c

@@ -98,6 +98,7 @@ int main(int argc, char *argv[])
 			{ "pidfile", required_argument, 0, 46},
 			{ "veth-pair", required_argument, 0, 47},
 			{ "action-script", required_argument, 0, 49},
+			{ LREMAP_PARAM, no_argument, 0, 41},
 			{ },
 		};
 
@@ -160,6 +161,10 @@ int main(int argc, char *argv[])
 					log_level++;
 			}
 			break;
+		case 41:
+			pr_info("Will allow link remaps on FS\n");
+			opts.link_remap_ok = true;
+			break;
 		case 42:
 			pr_info("Will dump TCP connections\n");
 			opts.tcp_established_ok = true;
@@ -302,6 +307,7 @@ usage:
 	pr_msg("  -r|--root [PATH]	change the root filesystem (when run in mount namespace)\n");
 	pr_msg("  --evasive-devices	use any path to a device file if the original one is inaccessible\n");
 	pr_msg("  --veth-pair [IN=OUT]	correspondence between outside and inside names of veth devices\n");
+	pr_msg("  --link-remap          allow to link unlinked files back when possible (modifies FS till restore)\n");
 	pr_msg("  --action-script [SCR]	add an external action script\n");
 	pr_msg("			The environment variable CRTOOL_SCRIPT_ACTION contains one of the actions:\n");
 	pr_msg("			* network-lock - lock network in a target network namespace");

files-reg.c

@@ -285,6 +285,12 @@ static int create_link_remap(char *path, int len, int lfd, u32 *idp)
 	RegFileEntry rfe = REG_FILE_ENTRY__INIT;
 	FownEntry fwn = FOWN_ENTRY__INIT;
 
+	if (!opts.link_remap_ok) {
+		pr_err("Can't create link remap for %s. "
+				"Use " LREMAP_PARAM " option.\n", path);
+		return -1;
+	}
+
 	/*
 	 * Linked remapping -- we create a hard link on a removed file
 	 * in the directory original file used to sit.

include/crtools.h

@@ -95,6 +95,7 @@ struct cr_options {
 	bool			ext_unix_sk;
 	bool			tcp_established_ok;
 	bool			evasive_devices;
+	bool			link_remap_ok;
 	unsigned int		namespaces_flags;
 	bool			log_file_per_pid;
 	char			*output;

include/files.h

@@ -95,4 +95,6 @@ extern int set_fd_flags(int fd, int flags);
 #define AT_EMPTY_PATH 0x1000
 #endif
 
+#define LREMAP_PARAM	"link-remap"
+
 #endif /* FILES_H_ */

test/zdtm.sh

@@ -232,7 +232,7 @@ EOF
 	echo Dump $PID
 	mkdir -p $ddump
 	save_fds $PID  $ddump/dump.fd
-	setsid $CRTOOLS dump --tcp-established -x --evasive-devices -D $ddump -o dump.log -v 4 -t $PID $args $ARGS || {
+	setsid $CRTOOLS dump --tcp-established --link-remap -x --evasive-devices -D $ddump -o dump.log -v 4 -t $PID $args $ARGS || {
 		echo WARNING: process $tname is left running for your debugging needs
 		return 1
 	}