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 and made init happen as part of the fuse load/reload.

I also added the runtime field to the lxcfs_opts struct and upped its version for backwards compatibility.

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

src/bindings.c

@@ -763,7 +763,7 @@ 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;
 	}
 
@@ -894,7 +894,19 @@ static void sigusr2_toggle_virtualization(int signo, siginfo_t *info, void *extr
 	return;
 }
 
-static void __attribute__((constructor)) lxcfs_init(void)
+bool set_runtime_path(const char* new_path)
+{
+        if (new_path && strlen(new_path) < PATH_MAX) {
+                strcpy(runtime_path, new_path);
+                lxcfs_info("Using runtime path %s", runtime_path);
+                return true;
+        } else {
+		lxcfs_error("%s\n", "Failed to overwrite the runtime path");
+                return false;
+        }
+}
+
+void lxcfslib_init(void)
 {
 	__do_close int init_ns = -EBADF, root_fd = -EBADF,
 				  pidfd = -EBADF;
@@ -903,7 +915,7 @@ static void __attribute__((constructor)) lxcfs_init(void)
 	pid_t pid;
 	struct hierarchy *hierarchy;
 
-	lxcfs_info("Running constructor %s to reload liblxcfs", __func__);
+	lxcfs_info("Running %s to reload liblxcfs", __func__);
 
 	cgroup_ops = cgroup_init();
 	if (!cgroup_ops) {
@@ -1007,5 +1019,14 @@ 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;
+
+	const struct lxcfs_opts *opts = fc->private_data;
+        // We can read runtime_path as of opts version 2.
+        if (opts->version >= 2) {
+                set_runtime_path(opts->runtime_path);
+        }
+
+        /* initialize the library */
+        lxcfslib_init();        
+        return fc ? fc->private_data : NULL;
 }

src/bindings.h

@@ -107,6 +107,8 @@ struct lxcfs_opts {
 	bool swap_off;
 	bool use_pidfd;
 	bool use_cfs;
+        // As of opts version 2.
+        char runtime_path[PATH_MAX];
 	/*
 	 * Ideally we'd version by size but because of backwards compatability
 	 * and the use of bool instead of explicited __u32 and __u64 we can't.

src/lxcfs.c

@@ -32,7 +32,11 @@
 #include "macro.h"
 #include "memory_utils.h"
 
+#define PID_FILE "/lxcfs.pid"
+
 void *dlopen_handle;
+static char runtime_path[PATH_MAX] = DEFAULT_RUNTIME_PATH;
+
 
 /* Functions to keep track of number of threads using the library */
 
@@ -146,7 +150,7 @@ 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);
@@ -199,13 +203,12 @@ 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:
-	/* initialize the library */
-	if (reinit && lxcfs_init_library() < 0) {
+good: 
+	if (reinit && do_lxcfs_fuse_init() < 0) {
 		log_exit("Failed to initialize liblxcfs.so");
 	}
 
@@ -1119,7 +1122,7 @@ 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
@@ -1193,6 +1196,8 @@ static void usage(void)
 	lxcfs_info("  --enable-cfs         Enable CPU virtualization via CPU shares");
 	lxcfs_info("  --enable-pidfd       Use pidfd for process tracking");
 	lxcfs_info("  --enable-cgroup      Enable cgroup emulation code");
+	lxcfs_info("  --runtime-dir=DIR    Path to use as the runtime directory.");
+	lxcfs_info("                       Default is %s", DEFAULT_RUNTIME_PATH);
 	exit(EXIT_FAILURE);
 }
 
@@ -1244,6 +1249,7 @@ static const struct option long_options[] = {
 	{"enable-cgroup",	no_argument,		0,	  0	},
 
 	{"pidfile",		required_argument,	0,	'p'	},
+	{"runtime-dir",		required_argument,	0,	  0	},
 	{								},
 };
 
@@ -1286,7 +1292,7 @@ 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 + sizeof(PID_FILE)] = {};
 	bool debug = false, foreground = false;
 #if !HAVE_FUSE3
 	bool nonempty = false;
@@ -1303,6 +1309,7 @@ int main(int argc, char *argv[])
 	char *new_fuse_opts = NULL;
 	char *const *new_argv;
 	struct lxcfs_opts *opts;
+        char *runtime_path_arg = NULL;
 
 	opts = malloc(sizeof(struct lxcfs_opts));
 	if (opts == NULL) {
@@ -1313,7 +1320,7 @@ int main(int argc, char *argv[])
 	opts->swap_off = false;
 	opts->use_pidfd = false;
 	opts->use_cfs = false;
-	opts->version = 1;
+	opts->version = 2;
 
 	while ((c = getopt_long(argc, argv, "dulfhvso:p:", long_options, &idx)) != -1) {
 		switch (c) {
@@ -1324,6 +1331,8 @@ int main(int argc, char *argv[])
 				opts->use_cfs = true;
 			else if (strcmp(long_options[idx].name, "enable-cgroup") == 0)
 				cgroup_is_enabled = true;
+			else if (strcmp(long_options[idx].name, "runtime-dir") == 0)
+				runtime_path_arg = optarg;
 			else
 				usage();
 			break;
@@ -1376,6 +1385,12 @@ int main(int argc, char *argv[])
 		goto out;
 	}
 
+        if (runtime_path_arg) {
+                strcpy(runtime_path, runtime_path_arg);
+                lxcfs_info("runtime path set to %s", runtime_path);
+        }
+        strcpy(opts->runtime_path, runtime_path);
+
 	fuse_argv[fuse_argc++] = argv[0];
 	if (debug)
 		fuse_argv[fuse_argc++] = "-d";
@@ -1467,6 +1482,7 @@ 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;
@@ -1480,7 +1496,7 @@ int main(int argc, char *argv[])
 #endif
 
 	if (!pidfile) {
-		snprintf(pidfile_buf, sizeof(pidfile_buf), "%s/lxcfs.pid", DEFAULT_RUNTIME_PATH);
+                snprintf(pidfile_buf, sizeof(pidfile_buf), "%s%s", runtime_path, PID_FILE);
 		pidfile = pidfile_buf;
 	}