config/rpc: add new option --mntns-compat-mode for old mount engine

We plan to switch to Mounts-v2 engine for restoring mounts by default,
this options is to allow switching to old engine. This patch only adds
an option, no engine behind it yet.

Cherry-picked from Virtuozzo criu:
https://src.openvz.org/projects/OVZ/repos/criu/commits/503f9ad2c

Changes: allow --mntns-compat-mode option only on restore and only if
MOVE_MOUNT_SET_GROUP is supported (this also requires change in
unittest/mock.c), change id in rpc criu_opts.

Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>

criu/Makefile.crtools

@@ -41,6 +41,7 @@ obj-y			+= lsm.o
 obj-y			+= mem.o
 obj-y			+= memfd.o
 obj-y			+= mount.o
+obj-y			+= mount-v2.o
 obj-y			+= filesystems.o
 obj-y			+= namespaces.o
 obj-y			+= netfilter.o

criu/config.c

@@ -20,6 +20,7 @@
 #include "file-lock.h"
 #include "irmap.h"
 #include "mount.h"
+#include "mount-v2.h"
 #include "namespaces.h"
 #include "net.h"
 #include "sk-inet.h"
@@ -697,6 +698,7 @@ int parse_options(int argc, char **argv, bool *usage_error, bool *has_exec_cmd,
 		{ "file-validation", required_argument, 0, 1098 },
 		{ "lsm-mount-context", required_argument, 0, 1099 },
 		{ "network-lock", required_argument, 0, 1100 },
+		BOOL_OPT("mntns-compat-mode", &opts.mntns_compat_mode),
 		{},
 	};
 
@@ -1103,6 +1105,16 @@ int check_options(void)
 	}
 #endif
 
+	if (opts.mntns_compat_mode && opts.mode != CR_RESTORE) {
+		pr_err("Option --mntns-compat-mode is only valid on restore\n");
+		return 1;
+	} else if (!opts.mntns_compat_mode && opts.mode == CR_RESTORE) {
+		if (check_mount_v2()) {
+			pr_warn("Mount engine fallback to --mntns-compat-mode mode\n");
+			opts.mntns_compat_mode = true;
+		}
+	}
+
 	if (check_namespace_opts()) {
 		pr_err("Error: namespace flags conflict\n");
 		return 1;

criu/cr-service.c

@@ -719,6 +719,9 @@ static int setup_opts_from_req(int sk, CriuOpts *req)
 			goto err;
 	}
 
+	if (req->mntns_compat_mode)
+		opts.mntns_compat_mode = true;
+
 	log_set_loglevel(opts.log_level);
 	if (check_options())
 		goto err;

criu/crtools.c

@@ -408,6 +408,9 @@ usage:
 	       "                        in lazy-pages mode: 'criu lazy-pages -D DIR'\n"
 	       "                        --lazy-pages and lazy-pages mode require userfaultfd\n"
 	       "  --stream              dump/restore images using criu-image-streamer\n"
+	       "  --mntns-compat-mode   Use mount engine in compatibility mode. By default criu\n"
+	       "                        tries to use mount-v2 mode with more reliable algorithm\n"
+	       "                        based on MOVE_MOUNT_SET_GROUP kernel feature\n"
 	       "  --network-lock METHOD\n"
 	       "                      network locking/unlocking method; argument\n"
 	       "                      can be 'nftables' or 'iptables' (default).\n"

criu/include/cr_options.h

@@ -207,6 +207,8 @@ struct cr_options {
 
 	/* Shows the mode criu is running at the moment: dump/pre-dump/restore/... */
 	enum criu_mode mode;
+
+	int mntns_compat_mode;
 };
 
 extern struct cr_options opts;

criu/include/mount-v2.h

@@ -55,4 +55,6 @@ static inline long sys_openat2(int dirfd, const char *pathname, struct open_how
 	return syscall(__NR_openat2, dirfd, pathname, how, size);
 }
 
+extern int check_mount_v2(void);
+
 #endif /* __CR_MOUNT_V2_H__ */

criu/mount-v2.c

@@ -0,0 +1,20 @@
+#include "kerndat.h"
+#include "log.h"
+
+#undef LOG_PREFIX
+#define LOG_PREFIX "mnt-v2: "
+
+int check_mount_v2(void)
+{
+	if (!kdat.has_move_mount_set_group) {
+		pr_warn("Mounts-v2 requires MOVE_MOUNT_SET_GROUP support\n");
+		return -1;
+	}
+
+	if (!kdat.has_openat2) {
+		pr_warn("Mounts-v2 requires openat2 support\n");
+		return -1;
+	}
+
+	return 0;
+}

criu/unittest/mock.c

@@ -136,3 +136,8 @@ struct kerndat_s kdat = {};
 int service_fd_rlim_cur;
 
 unsigned __page_size;
+
+int check_mount_v2(void)
+{
+	return 0;
+}

images/rpc.proto

@@ -137,6 +137,7 @@ message criu_opts {
 	optional int32			pidfd_store_sk		= 62;
 	optional string			lsm_mount_context	= 63;
 	optional criu_network_lock_method	network_lock		= 64 [default = IPTABLES];
+	optional bool			mntns_compat_mode	= 65;
 /*	optional bool			check_mounts		= 128;	*/
 }
 

lib/c/criu.c

@@ -1170,6 +1170,17 @@ int criu_set_page_server_address_port(const char *address, int port)
 	return criu_local_set_page_server_address_port(global_opts, address, port);
 }
 
+void criu_local_set_mntns_compat_mode(criu_opts *opts, bool val)
+{
+	opts->rpc->has_mntns_compat_mode = true;
+	opts->rpc->mntns_compat_mode = val;
+}
+
+void criu_set_mntns_compat_mode(bool val)
+{
+	criu_local_set_mntns_compat_mode(global_opts, val);
+}
+
 static CriuResp *recv_resp(int socket_fd)
 {
 	struct msghdr msg_hdr = { 0 };

lib/c/criu.h

@@ -112,6 +112,7 @@ int criu_set_pre_dump_mode(enum criu_pre_dump_mode mode);
 void criu_set_pidfd_store_sk(int sk);
 int criu_set_network_lock(enum criu_network_lock_method method);
 int criu_join_ns_add(const char *ns, const char *ns_file, const char *extra_opt);
+void criu_set_mntns_compat_mode(bool val);
 
 /*
  * The criu_notify_arg_t na argument is an opaque
@@ -275,6 +276,7 @@ int criu_local_set_pre_dump_mode(criu_opts *opts, enum criu_pre_dump_mode mode);
 void criu_local_set_pidfd_store_sk(criu_opts *opts, int sk);
 int criu_local_set_network_lock(criu_opts *opts, enum criu_network_lock_method method);
 int criu_local_join_ns_add(criu_opts *opts, const char *ns, const char *ns_file, const char *extra_opt);
+void criu_local_set_mntns_compat_mode(criu_opts *opts, bool val);
 
 void criu_local_set_notify_cb(criu_opts *opts, int (*cb)(char *action, criu_notify_arg_t na));