#include <inttypes.h>
#include <urcu/list.h>
#include <urcu/uatomic.h>
+#include <sys/stat.h>
#include <common/defaults.h>
#include <common/common.h>
#include "cmd.h"
+/* Sleep for 100ms between each check for the shm path's deletion. */
+#define SESSION_DESTROY_SHM_PATH_CHECK_DELAY_US 100000
+
+static enum lttng_error_code wait_on_path(void *path);
+
+/*
+ * Command completion handler that is used by the destroy command
+ * when a session that has a non-default shm_path is being destroyed.
+ *
+ * See comment in cmd_destroy_session() for the rationale.
+ */
+static struct destroy_completion_handler {
+ struct cmd_completion_handler handler;
+ char shm_path[member_sizeof(struct ltt_session, shm_path)];
+} destroy_completion_handler = {
+ .handler = {
+ .run = wait_on_path,
+ .data = destroy_completion_handler.shm_path
+ },
+ .shm_path = { 0 },
+};
+
+static struct cmd_completion_handler *current_completion_handler;
+
/*
* Used to keep a unique index for each relayd socket created where this value
* is associated with streams on the consumer so it can match the right relayd
PERROR("write kernel poll pipe");
}
+ if (session->shm_path[0]) {
+ /*
+ * When a session is created with an explicit shm_path,
+ * the consumer daemon will create its shared memory files
+ * at that location and will *not* unlink them. This is normal
+ * as the intention of that feature is to make it possible
+ * to retrieve the content of those files should a crash occur.
+ *
+ * To ensure the content of those files can be used, the
+ * sessiond daemon will replicate the content of the metadata
+ * cache in a metadata file.
+ *
+ * On clean-up, it is expected that the consumer daemon will
+ * unlink the shared memory files and that the session daemon
+ * will unlink the metadata file. Then, the session's directory
+ * in the shm path can be removed.
+ *
+ * Unfortunately, a flaw in the design of the sessiond's and
+ * consumerd's tear down of channels makes it impossible to
+ * determine when the sessiond _and_ the consumerd have both
+ * destroyed their representation of a channel. For one, the
+ * unlinking, close, and rmdir happen in deferred 'call_rcu'
+ * callbacks in both daemons.
+ *
+ * However, it is also impossible for the sessiond to know when
+ * the consumer daemon is done destroying its channel(s) since
+ * it occurs as a reaction to the closing of the channel's file
+ * descriptor. There is no resulting communication initiated
+ * from the consumerd to the sessiond to confirm that the
+ * operation is completed (and was successful).
+ *
+ * Until this is all fixed, the session daemon checks for the
+ * removal of the session's shm path which makes it possible
+ * to safely advertise a session as having been destroyed.
+ *
+ * Prior to this fix, it was not possible to reliably save
+ * a session making use of the --shm-path option, destroy it,
+ * and load it again. This is because the creation of the
+ * session would fail upon seeing the session's shm path
+ * already in existence.
+ *
+ * Note that none of the error paths in the check for the
+ * directory's existence return an error. This is normal
+ * as there isn't much that can be done. The session will
+ * be destroyed properly, except that we can't offer the
+ * guarantee that the same session can be re-created.
+ */
+ current_completion_handler = &destroy_completion_handler.handler;
+ ret = lttng_strncpy(destroy_completion_handler.shm_path,
+ session->shm_path,
+ sizeof(destroy_completion_handler.shm_path));
+ assert(!ret);
+ }
ret = session_destroy(session);
return ret;
return ret;
}
+/* Wait for a given path to be removed before continuing. */
+static enum lttng_error_code wait_on_path(void *path_data)
+{
+ const char *shm_path = path_data;
+
+ DBG("Waiting for the shm path at %s to be removed before completing session destruction",
+ shm_path);
+ while (true) {
+ int ret;
+ struct stat st;
+
+ ret = stat(shm_path, &st);
+ if (ret) {
+ if (errno != ENOENT) {
+ PERROR("stat() returned an error while checking for the existence of the shm path");
+ } else {
+ DBG("shm path no longer exists, completing the destruction of session");
+ }
+ break;
+ } else {
+ if (!S_ISDIR(st.st_mode)) {
+ ERR("The type of shm path %s returned by stat() is not a directory; aborting the wait for shm path removal",
+ shm_path);
+ break;
+ }
+ }
+ usleep(SESSION_DESTROY_SHM_PATH_CHECK_DELAY_US);
+ }
+ return LTTNG_OK;
+}
+
+/*
+ * Returns a pointer to a handler to run on completion of a command.
+ * Returns NULL if no handler has to be run for the last command executed.
+ */
+const struct cmd_completion_handler *cmd_pop_completion_handler(void)
+{
+ struct cmd_completion_handler *handler = current_completion_handler;
+
+ current_completion_handler = NULL;
+ return handler;
+}
+
/*
* Init command subsystem.
*/
projects / lttng-tools.git / blobdiff