friendly to daemon

Signed-off-by: Rongsong Shen <rshen@shenrs.eu>

libmcount/internal.h

@@ -185,7 +185,7 @@ extern uint64_t mcount_threshold; /* nsec */
 extern unsigned mcount_minsize;
 extern pthread_key_t mtd_key;
 extern int shmem_bufsize;
-extern int pfd;
+extern int mcount_get_pfd(void);
 extern int mcount_depth;
 extern char *mcount_exename;
 extern int page_size_in_kb;

libmcount/mcount.c

@@ -58,9 +58,6 @@ pthread_key_t mtd_key = (pthread_key_t)-1;
 /* thread local data to trace function execution */
 TLS struct mcount_thread_data mtd;
 
-/* pipe file descriptor to communite to uftrace */
-int pfd = -1;
-
 /* maximum depth of mcount rstack */
 static int mcount_rstack_max = MCOUNT_RSTACK_MAX;
 
@@ -518,6 +515,7 @@ static void send_session_msg(struct mcount_thread_data *mtdp, const char *sess_i
 		},
 	};
 	int len = sizeof(msg) + msg.len;
+	int pfd = mcount_get_pfd();
 
 	if (pfd < 0)
 		return;
@@ -528,6 +526,8 @@ static void send_session_msg(struct mcount_thread_data *mtdp, const char *sess_i
 		if (!mcount_should_stop())
 			pr_err("write tid info failed");
 	}
+
+	close(pfd);
 }
 
 static void mcount_trace_finish(bool send_msg)
@@ -547,11 +547,6 @@ static void mcount_trace_finish(bool send_msg)
 	if (send_msg)
 		uftrace_send_message(UFTRACE_MSG_FINISH, NULL, 0);
 
-	if (pfd != -1) {
-		close(pfd);
-		pfd = -1;
-	}
-
 	trace_finished = true;
 	pr_dbg("mcount trace finished\n");
 
@@ -1802,9 +1797,28 @@ static void mcount_script_init(enum uftrace_pattern_type patt_type)
 	strv_free(&info.cmds);
 }
 
-static __used void mcount_startup(void)
+int mcount_get_pfd(void)
 {
+	char *dirname;
 	char *channel = NULL;
+	int pfd;
+
+	dirname = getenv("UFTRACE_DIR");
+	if (dirname == NULL)
+		dirname = UFTRACE_DIR_NAME;
+
+	xasprintf(&channel, "%s/%s", dirname, ".channel");
+	pfd = open(channel, O_WRONLY);
+	free(channel);
+
+	if (pfd >= 0)
+		lseek(pfd, (off_t)0, SEEK_END);
+
+	return pfd;
+}
+
+static __used void mcount_startup(void)
+{
 	char *logfd_str;
 	char *debug_str;
 	char *bufsize_str;
@@ -1885,10 +1899,6 @@ static __used void mcount_startup(void)
 	if (dirname == NULL)
 		dirname = UFTRACE_DIR_NAME;
 
-	xasprintf(&channel, "%s/%s", dirname, ".channel");
-	pfd = open(channel, O_WRONLY);
-	free(channel);
-
 	if (getenv("UFTRACE_LIST_EVENT")) {
 		mcount_list_events();
 		exit(0);

libmcount/misc.c

@@ -75,6 +75,7 @@ void uftrace_send_message(int type, void *data, size_t len)
 			.iov_len = len,
 		},
 	};
+	int pfd = mcount_get_pfd();
 
 	if (pfd < 0)
 		return;
@@ -84,6 +85,7 @@ void uftrace_send_message(int type, void *data, size_t len)
 		if (!mcount_should_stop())
 			pr_err("writing shmem name to pipe");
 	}
+	close(pfd);
 }
 
 void build_debug_domain(char *dbg_domain_str)

libmcount/wrap.c

@@ -62,6 +62,7 @@ static void send_dlopen_msg(struct mcount_thread_data *mtdp, const char *sess_id
 		},
 	};
 	int len = sizeof(msg) + msg.len;
+	int pfd = mcount_get_pfd();
 
 	if (pfd < 0)
 		return;
@@ -72,6 +73,8 @@ static void send_dlopen_msg(struct mcount_thread_data *mtdp, const char *sess_id
 		if (!mcount_should_stop())
 			pr_err("write tid info failed");
 	}
+
+	close(pfd);
 }
 
 static int dlopen_base_callback(struct dl_phdr_info *info, size_t size, void *arg)