map shared memory for rendez-vous with non-responding sessiond

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/include/lttng-ust-comm.h b/include/lttng-ust-comm.h
index e896f1a1015f3e52f042c0f8df1b8e3724715d5e..f06872b1bdb6ef2cebc4588bbbfcbc82da3410dc 100644 (file)
--- a/include/lttng-ust-comm.h
+++ b/include/lttng-ust-comm.h
@@ -46,6 +46,9 @@
 #define DEFAULT_HOME_APPS_UNIX_SOCK         "%s/.apps-ltt-sessiond"
 #define DEFAULT_HOME_CLIENT_UNIX_SOCK       "%s/.client-ltt-sessiond"
 
+#define DEFAULT_GLOBAL_APPS_WAIT_SHM_PATH   "/lttng-ust-apps-wait"
+#define DEFAULT_HOME_APPS_WAIT_SHM_PATH     "/%u-lttng-ust-apps-wait"
+
 /* Queue size of listen(2) */
 #define MAX_LISTEN 10
 

diff --git a/libust/lttng-ust-comm.c b/libust/lttng-ust-comm.c
index e76807975c1b4a1af15fbe8f0950fa238b5c9176..37527290a6f36a67f294f24b6248f9668e16b96e 100644 (file)
--- a/libust/lttng-ust-comm.c
+++ b/libust/lttng-ust-comm.c
@@ -22,6 +22,9 @@
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <sys/prctl.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 #include <unistd.h>
 #include <errno.h>
 #include <pthread.h>
@@ -74,30 +77,39 @@ static int sem_count = { 2 };
  */
 struct sock_info {
        const char *name;
-       char sock_path[PATH_MAX];
-       int socket;
        pthread_t ust_listener; /* listener thread */
        int root_handle;
        int constructor_sem_posted;
        int allowed;
+
+       char sock_path[PATH_MAX];
+       int socket;
+
+       char wait_shm_path[PATH_MAX];
+       char *wait_shm_mmap;
 };
 
 /* Socket from app (connect) to session daemon (listen) for communication */
 struct sock_info global_apps = {
        .name = "global",
-       .sock_path = DEFAULT_GLOBAL_APPS_UNIX_SOCK,
-       .socket = -1,
+
        .root_handle = -1,
        .allowed = 1,
+
+       .sock_path = DEFAULT_GLOBAL_APPS_UNIX_SOCK,
+       .socket = -1,
+
+       .wait_shm_path = DEFAULT_GLOBAL_APPS_WAIT_SHM_PATH,
 };
 
 /* TODO: allow global_apps_sock_path override */
 
 struct sock_info local_apps = {
        .name = "local",
-       .socket = -1,
        .root_handle = -1,
        .allowed = 0,   /* Check setuid bit first */
+
+       .socket = -1,
 };
 
 extern void ltt_ring_buffer_client_overwrite_init(void);
@@ -111,11 +123,13 @@ static
 int setup_local_apps(void)
 {
        const char *home_dir;
+       uid_t uid;
 
+       uid = getuid();
        /*
         * Disallow per-user tracing for setuid binaries.
         */
-       if (getuid() != geteuid()) {
+       if (uid != geteuid()) {
                local_apps.allowed = 0;
                return 0;
        } else {
@@ -126,6 +140,8 @@ int setup_local_apps(void)
                return -ENOENT;
        snprintf(local_apps.sock_path, PATH_MAX,
                 DEFAULT_HOME_APPS_UNIX_SOCK, home_dir);
+       snprintf(local_apps.wait_shm_path, PATH_MAX,
+                DEFAULT_HOME_APPS_WAIT_SHM_PATH, uid);
        return 0;
 }
 
@@ -268,7 +284,7 @@ void cleanup_sock_info(struct sock_info *sock_info)
        if (sock_info->socket != -1) {
                ret = close(sock_info->socket);
                if (ret) {
-                       ERR("Error closing local apps socket");
+                       ERR("Error closing apps socket");
                }
                sock_info->socket = -1;
        }
@@ -280,6 +296,117 @@ void cleanup_sock_info(struct sock_info *sock_info)
                sock_info->root_handle = -1;
        }
        sock_info->constructor_sem_posted = 0;
+       if (sock_info->wait_shm_mmap) {
+               ret = munmap(sock_info->wait_shm_mmap, sysconf(_SC_PAGE_SIZE));
+               if (ret) {
+                       ERR("Error unmapping wait shm");
+               }
+               sock_info->wait_shm_mmap = NULL;
+       }
+}
+
+static
+char *get_map_shm(struct sock_info *sock_info)
+{
+       size_t mmap_size = sysconf(_SC_PAGE_SIZE);
+       int wait_shm_fd, ret;
+       char *wait_shm_mmap;
+
+       /*
+        * Get existing (read-only) shm, or open new shm.
+        * First try to open read-only.
+        */
+       wait_shm_fd = shm_open(sock_info->wait_shm_path,
+                       O_RDONLY, 0700);
+       if (wait_shm_fd >= 0)
+               goto got_shm;
+       /*
+        * Real-only open did not work. If it is because it did
+        * not exist, try creating it. Else it's a failure that
+        * prohibits using shm.
+        */
+       if (errno != ENOENT) {
+               ERR("Error opening shm %s", sock_info->wait_shm_path);
+               goto error;
+       }
+       wait_shm_fd = shm_open(sock_info->wait_shm_path,
+                       O_RDWR | O_CREAT | O_EXCL, 0700);
+       if (wait_shm_fd >= 0)
+               goto created_shm;
+       if (errno != EEXIST) {
+               ERR("Error opening shm %s", sock_info->wait_shm_path);
+               goto error;
+       }
+       /*
+        * If another process beat us to create the shm, we are
+        * pretty certain the shm is available for us in
+        * read-only mode.
+        */
+       wait_shm_fd = shm_open(sock_info->wait_shm_path,
+                       O_RDWR | O_CREAT | O_EXCL, 0700);
+       if (wait_shm_fd >= 0)
+               goto got_shm;
+       else
+               goto error;
+
+created_shm:
+       ret = ftruncate(wait_shm_fd, mmap_size);
+       if (ret) {
+               PERROR("ftruncate");
+               ret = close(wait_shm_fd);
+               if (ret) {
+                       ERR("Error closing fd");
+               }
+               wait_shm_fd = -1;
+               goto error;
+       }
+got_shm:
+       wait_shm_mmap = mmap(NULL, mmap_size, PROT_READ,
+                 MAP_SHARED, wait_shm_fd, 0);
+       if (wait_shm_mmap == MAP_FAILED) {
+               PERROR("mmap");
+               goto error;
+       }
+       /* close shm fd immediately after taking the mmap reference */
+       ret = close(wait_shm_fd);
+       if (ret) {
+               ERR("Error closing fd");
+       }
+       return wait_shm_mmap;
+
+error:
+       return NULL;
+}
+
+static
+void wait_for_sessiond(struct sock_info *sock_info)
+{
+       ust_lock();
+       if (lttng_ust_comm_should_quit) {
+               goto quit;
+       }
+       if (!sock_info->wait_shm_mmap) {
+               sock_info->wait_shm_mmap = get_map_shm(sock_info);
+               if (!sock_info->wait_shm_mmap)
+                       goto error;
+       }
+       ust_unlock();
+
+       DBG("Waiting for %s apps sessiond", sock_info->name);
+       /* Wait for futex wakeup TODO */
+       sleep(5);
+
+       return;
+
+quit:
+       ust_unlock();
+       return;
+
+error:
+       ust_unlock();
+       /* Error handling: fallback on a 5 seconds sleep. */
+       sleep(5);
+       return;
 }
 
 /*
@@ -312,8 +439,6 @@ restart:
                sock_info->socket = -1;
        }
 
-       /* Check for sessiond availability with pipe TODO */
-
        /* Register */
        ret = lttcomm_connect_unix_sock(sock_info->sock_path);
        if (ret < 0) {
@@ -325,7 +450,9 @@ restart:
                ret = handle_register_done(sock_info);
                assert(!ret);
                ust_unlock();
-               sleep(5);
+
+               /* Wait for sessiond availability with pipe */
+               wait_for_sessiond(sock_info);
                goto restart;
        }
 
@@ -355,7 +482,7 @@ restart:
                ret = handle_register_done(sock_info);
                assert(!ret);
                ust_unlock();
-               sleep(5);
+               wait_for_sessiond(sock_info);
                goto restart;
        }
        ust_unlock();