Add a flag for overriding the runtime dir.

Adds a --runtime-dir cli flag which overrides the /run dir in the lxcfslib. This ended up being kind of tricky because of how lxcfslib can be reloaded and its use of a library constructor. In order read the cli flag and then set a variable in the library, I removed the contstructor attribute and made it an explicit call in order to override the runtime dir in between loading the library and initializing lxcfslib.

Signed-off-by: Sebastien Dabdoub <[email protected]>

src/bindings.c

@@ -761,7 +761,7 @@ static int permute_prepare(void)
 	}
 
 	if (mount(runtime_path, new_runtime, NULL, MS_BIND, 0) < 0) {
-		lxcfs_error("Failed to bind-mount /run into new root: %s.\n", strerror(errno));
+		lxcfs_error("Failed to bind-mount %s into new root: %s.\n", runtime_path, strerror(errno));
 		return -1;
 	}
 
@@ -892,7 +892,7 @@ static void sigusr2_toggle_virtualization(int signo, siginfo_t *info, void *extr
 	return;
 }
 
-static void __attribute__((constructor)) lxcfs_init(void)
+void lxcfslib_init(void)
 {
 	__do_close int init_ns = -EBADF, root_fd = -EBADF,
 				  pidfd = -EBADF;
@@ -1003,5 +1003,21 @@ void *lxcfs_fuse_init(struct fuse_conn_info *conn, void *data)
 	can_use_sys_cpu = true;
 #endif
 	has_versioned_opts = true;
-	return fc ? fc->private_data : NULL;
+        return fc ? fc->private_data : NULL;
+}
+
+bool set_runtime_path(const char* new_path)
+{
+        int pathlen;
+
+        if (new_path && strlen(new_path) < PATH_MAX) {
+                pathlen = strlen(new_path);
+                memcpy(runtime_path, new_path, pathlen);
+                runtime_path[pathlen] = '\0';
+                lxcfs_info("Using runtime path %s", runtime_path);
+                return true;
+        } else {
+		lxcfs_error("%s\n", "Failed to overwrite the runtime path");
+                return false;
+        }
 }

src/bindings.h

@@ -183,4 +183,9 @@ static inline pid_t lxcfs_clone(int (*fn)(void *), void *arg, int flags)
 
 __visible extern void *lxcfs_fuse_init(struct fuse_conn_info *conn, void *data);
 
+// Overrides the runtime path from DEFAULT_RUNTIME_PATH - /var/run
+__visible extern bool set_runtime_path(const char* runtime_path);
+// Needs to be called on library load/reload.
+__visible extern void lxcfslib_init(void);
+
 #endif /* __LXCFS_BINDINGS_H */

src/lxcfs.c

@@ -33,6 +33,7 @@
 #include "memory_utils.h"
 
 void *dlopen_handle;
+static char runtime_path[PATH_MAX];
 
 /* Functions to keep track of number of threads using the library */
 
@@ -146,7 +147,7 @@ static int stop_loadavg(void)
 
 static volatile sig_atomic_t need_reload;
 
-static int lxcfs_init_library(void)
+static int do_lxcfs_fuse_init(void)
 {
 	char *error;
 	void *(*__lxcfs_fuse_init)(struct fuse_conn_info * conn, void * cfg);
@@ -162,6 +163,39 @@ static int lxcfs_init_library(void)
 	return 0;
 }
 
+static int do_lxcfslib_init(void)
+{
+	char *error;
+	void (*__lxcfslib_init)(void);
+
+	dlerror();
+	__lxcfslib_init = (void (*)(void))dlsym(dlopen_handle, "lxcfslib_init");
+	error = dlerror();
+	if (error)
+		return log_error(-1, "%s - Failed to find lxcfslib_init()", error);
+
+	__lxcfslib_init();
+
+	return 0;
+}
+
+static bool do_set_runtime_path(const char *path)
+{
+	char *error;
+	bool (*__set_runtime_path)(const char *path);
+
+	dlerror();
+	__set_runtime_path = (bool (*)(const char *path))dlsym(dlopen_handle, "set_runtime_path");
+	error = dlerror();
+	if (error) {
+		log_error(-1, "%s - Failed to find set_runtime_path()", error);
+                return false;
+        }
+
+        lxcfs_info("set runtime path %s", path);
+	return __set_runtime_path(path);
+}
+
 /* do_reload - reload the dynamic library.  Done under
  * lock and when we know the user_count was 0 */
 static void do_reload(bool reinit)
@@ -199,13 +233,19 @@ static void do_reload(bool reinit)
 
         dlopen_handle = dlopen(lxcfs_lib_path, RTLD_LAZY);
 	if (!dlopen_handle)
-		log_exit("%s - Failed to open liblxcfs.so", dlerror());
+		log_exit("%s - Failed to open liblxcfs.so at %s", dlerror(), lxcfs_lib_path);
 	else
 		lxcfs_debug("Opened %s", lxcfs_lib_path);
 
 good:
+        if (strlen(runtime_path) > 0 && !do_set_runtime_path(runtime_path)) {
+		dlclose(dlopen_handle);
+		log_exit("failed to override runtime dir with %s", runtime_path);
+        }
+
 	/* initialize the library */
-	if (reinit && lxcfs_init_library() < 0) {
+        do_lxcfslib_init();
+	if (reinit && do_lxcfs_fuse_init() < 0) {
 		log_exit("Failed to initialize liblxcfs.so");
 	}
 
@@ -1117,7 +1157,7 @@ static void *lxcfs_init(struct fuse_conn_info *conn, struct fuse_config *cfg)
 static void *lxcfs_init(struct fuse_conn_info *conn)
 #endif
 {
-	if (lxcfs_init_library() < 0)
+	if (do_lxcfs_fuse_init() < 0)
 		return NULL;
 
 #if HAVE_FUSE3
@@ -1190,6 +1230,8 @@ static void usage(void)
 	lxcfs_info("  -v, --version        Print lxcfs version");
 	lxcfs_info("  --enable-cfs         Enable CPU virtualization via CPU shares");
 	lxcfs_info("  --enable-pidfd       Use pidfd for process tracking");
+	lxcfs_info("  --runtime-dir=DIR    Path to use as the runtime directory.");
+	lxcfs_info("                       Default is %s", DEFAULT_RUNTIME_PATH);
 	exit(EXIT_FAILURE);
 }
 
@@ -1240,6 +1282,7 @@ static const struct option long_options[] = {
 	{"enable-pidfd",	no_argument,		0,	  0	},
 
 	{"pidfile",		required_argument,	0,	'p'	},
+	{"runtime-dir",		required_argument,	0,	  0	},
 	{								},
 };
 
@@ -1282,7 +1325,7 @@ int main(int argc, char *argv[])
 	int pidfile_fd = -EBADF;
 	int ret = EXIT_FAILURE;
 	char *pidfile = NULL, *token = NULL;
-	char pidfile_buf[STRLITERALLEN(DEFAULT_RUNTIME_PATH) + STRLITERALLEN("/lxcfs.pid") + 1] = {};
+	char pidfile_buf[PATH_MAX] = {};
 	bool debug = false, foreground = false;
 #if !HAVE_FUSE3
 	bool nonempty = false;
@@ -1299,6 +1342,8 @@ int main(int argc, char *argv[])
 	char *new_fuse_opts = NULL;
 	char *const *new_argv;
 	struct lxcfs_opts *opts;
+        char *runtime_path_arg = NULL;
+        int runtime_path_len;
 
 	opts = malloc(sizeof(struct lxcfs_opts));
 	if (opts == NULL) {
@@ -1318,6 +1363,8 @@ int main(int argc, char *argv[])
 				opts->use_pidfd = true;
 			else if (strcmp(long_options[idx].name, "enable-cfs") == 0)
 				opts->use_cfs = true;
+			else if (strcmp(long_options[idx].name, "runtime-dir") == 0)
+				runtime_path_arg = optarg;
 			else
 				usage();
 			break;
@@ -1370,6 +1417,13 @@ int main(int argc, char *argv[])
 		goto out;
 	}
 
+        if (runtime_path_arg) {
+                runtime_path_len = strlen(runtime_path_arg);
+                memcpy(runtime_path, runtime_path_arg, runtime_path_len);
+                runtime_path[runtime_path_len] = '\0';
+                lxcfs_info("runtime path set to %s", runtime_path);
+        }
+
 	fuse_argv[fuse_argc++] = argv[0];
 	if (debug)
 		fuse_argv[fuse_argc++] = "-d";
@@ -1461,6 +1515,7 @@ int main(int argc, char *argv[])
 	lxcfs_info("Starting LXCFS at %s", argv[0]);
 
 	do_reload(false);
+
 	if (install_signal_handler(SIGUSR1, sigusr1_reload)) {
 		lxcfs_error("%s - Failed to install SIGUSR1 signal handler", strerror(errno));
 		goto out;
@@ -1474,7 +1529,10 @@ int main(int argc, char *argv[])
 #endif
 
 	if (!pidfile) {
-		snprintf(pidfile_buf, sizeof(pidfile_buf), "%s/lxcfs.pid", DEFAULT_RUNTIME_PATH);
+                if (runtime_path_arg)
+                        snprintf(pidfile_buf, sizeof(pidfile_buf), "%s/lxcfs.pid", runtime_path_arg);
+                else
+                        snprintf(pidfile_buf, sizeof(pidfile_buf), "%s/lxcfs.pid", DEFAULT_RUNTIME_PATH);
 		pidfile = pidfile_buf;
 	}